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Epistemics of the soul: Epistemic logics in German 18th‐century empirical psychology

Abstract This article examines epistemic logics in 18th‐century German empirical psychology and distinguishes three basic patterns at play throughout the century. First, as empirical psychology was introduced in the 1720s, it relied on the Aristotelian‐scholastic conception of experience as universal and evidently true propositions of how things typically behave in nature. Empirical psychology was here a matter of defining and demonstrating the general nature, structure, and functions of the soul by referring to experiences that most people could recognize as universally and evidently true. Second, around midcentury this logic was challenged as a new generation of philosopher‐physicians launched an empirical psychology based on extraordinary medical cases. Rather than focusing on the general and universal, this new strand of case‐based empirical psychology charted the individual, unique and often abnormal. Third, from the early 1770s, the interest in the individual was complemented by a new discourse on psychological method. Adopting the epistemic techniques developed within natural and experimental philosophy, empirical knowledge of the soul was seen as the result of rigorously conducted singular observations that were frequently repeated and carefully documented and analyzed. Rather than replacing one another sequentially, these three epistemic logics should be understood as cumulative. That is, despite sometimes profound differences, each new logic was layered on top of the existing ones, thereby broadening and increasing the epistemic complexity of empirical psychology.

Although Wolff distinguished conceptually between the two as early as the German Metaphysics (Vernünfftige Gedancken von Gott, der Welt und der Seele des Menschen, 1720), the terms "empirical psychology" and "rational psychology" first appeared in the Latin Logic (Philosophia rationalis sive logica, 1728), to then form the basis of the voluminous Empirical Psychology (Psychologia empirica, 1732) and Rational Psychology (Psychologia rationalis, 1734).
Whereas the former "establishes principles through experience," the latter examines "whatever is possible through the human soul" (Wolff, 1968, p. 1, §. 1, Wolff, 1994, p. 1, §. 1, Wolff, 1980b. 1 It has sometimes been suggested that Wolff's empirical psychology used a dedicated introspective method (Leventhal, 2019, pp. 115-116;Vidal, 2011, pp. 92-93). This is only partly true; Wolff's internal or introspective method was in fact not specific to psychology but rather was common to all empirical sciences. To explain how this can be the case we need to look closer at both the Wolffian method and the epistemic role of experience more broadly.
The Wolffian philosophy featured an all-embracing system of knowledge in which psychology or the science of the soul constituted a part of metaphysics (together with ontology, cosmology and natural theology) (Arndt, 1978;École, 1990;Frängsmyr, 1999;Gómez Tutor, 2004Schneiders, 1983;Wundt, 1964). Uniting the system as a whole was the universal demonstrative or mathematical method, whereby every truth could be demonstrated from other more fundamental truths till only axioms, definitions and empirical propositions remained (Gómez Tutor, 2018, 2004. The function of the empirical proposition was to state matters of experiential fact. In the highly popular German Logic (Vernünfftige Gedancken von den Kräften des menschlichen Verstandes, 1713) Wolff thus pedagogically defined experience (Erfahrung) as "everything that we recognize when we pay attention to our perceptions. For instance, I see that when a light is lit everything around me becomes visible; that the spilled water makes the table wet; that the flame of the light ignites the paper and so on. All such knowledge is called experience" (Wolff, 1978, p. 181, §. 1). 2 In the Latin Logic Wolff also called this basic form "historical knowledge" (cognitio historica). "For example, historical knowledge is possessed by him who knows from experience that the sun rises in the morning and sets in the evening, that at the beginning of spring the buds of trees blossom forth, that animals are propagated by generation, that we desire nothing except under the aspect of good" (Wolff, 1963, p. 3, Wolff, 1983a. 3 Wolff's conception of experience was not his own invention but reflected what can be referred to as the Aristotelian-scholastic notion of experience (Pomata, 2005;Pomata & Siraisi, 2005). 4 Aristotle thus remarked that experience is the result of many perceptions accumulated and stored in memory (Aristotle, 1995;2.19). In line with this logic, to use experience in science was, as the historian of science Peter Dear has remarked, typically a matter of forming universal and often evidently true statements either directly from memory or by reference to weighty authorities, rather than making actual observations (Dear, 1995, p. 22). To request observational proof of statements such as "heavy bodies fall" would have been pointless, simply for the reason that everyone already accepted them as true. In the case of Wolff, who adopted the demonstrative method largely from the scholastic tradition, this epistemic logic ran throughout his philosophy (Arndt, 1978;Frängsmyr, 1999;Wundt, 1964). In the German Logic, for instance, Wolff pointed out that When someone concludes from experience that the spilled water makes the table wet, it would be pointless if he referred to a specific case. Because it is a thing that occurs daily, there should be no one who has not had this experience several times. And if there would be someone who has never yet seen such an event he could easily pour water on the table and see that it becomes wet (Wolff, 1978, p. 182, §. 3). 5 In line with the Aristotelian-scholastic logic of experience, in such cases it would have been pointless to request or refer to specific singular observations. Although scholars have shown that the Wolffian production of empirical RYDBERG | 385 propositions required a methodologically rigorous internal operation, it was precisely by being evidently true and thus indubitable that these propositions were useful in scientific demonstrations (Gómez Tutor, 2018, 2004.
Having highlighted this basic epistemic logic, we are now in a position to return to psychology. Here as in other disciplines, the role of experience was to provide evidently true and indubitable propositions. These were then to serve as a basis for more complex scientific demonstrations. That this was how Wolff himself perceived the issue becomes strikingly clear in the introductory paragraph to the discussion of empirical psychology in the German Metaphysics.
I am not attempting here to show what the soul is and how changes take place in it, but my plan now is simply to tell what we perceive of it through our daily experience. And I don't want to state here anything beyond what anyone who pays attention to himself realizes. This will provide us with the basis from which other things can be deduced, which not everyone immediately realizes. Namely, from what we perceive of the soul we want to form clear concepts and now and again notice some important truths that can be demonstrated from these (Wolff, 1983c, pp. 106-107, §. 191). 6 For Wolff and the Wolffians, there was no epistemological problem regarding how to acquire empirical knowledge of the soul through observations simply because the production of such knowledge did not typically require actual observational practices. Instead, empirical knowledge was produced through an internal operation whereby perceptions stored in memory were refined into universal and evidently true empirical propositions. Since all empirical disciplines relied largely on this internal and, in a way, introspective operation, there was no need to develop a specific introspective method within empirical psychology.
To summarize, three principal points are particularly worth stressing. First, Wolff's empirical psychology reflected the Aristotelian-scholastic conception of experience. The fact that empirical propositions were typically produced by consulting memory explains why the soul was regarded as just one among many similar objects of knowledge. Second, in approaching the soul as an object that could be explored empirically as well as through demonstrations, Wolff was not original, but rather working within an established tradition and genre. Third, for those working in this tradition it would have made no sense to define psychology as a scientific discipline in the modern sense of the word. Not only did psychology lack its own methods, but its very justification as an area of study relied on its embeddedness in and intimate connection to other parts of philosophy. For this reason, any attempt to inscribe Wolff's empirical psychology in a larger disciplinary history of the birth of modern psychology runs the risk of seriously obscuring its very meaning and function.
The majority were orthodox, serving mainly to reproduce and spread Wolffian ideas. These had little impact over time; the future instead belonged to a new generation of eclectic works that typically combined the Wolffian method with other strands of thought. To understand the way in which these affected the development of empirical psychology it is necessary to take a step back and examine an alternative epistemic logic at play in Wolff's philosophy.
So far, I have drawn attention to the epistemic logic of the demonstrative method. There was, however, also a second type of reasoning that operated within Wolff's system, concerned with a kind of experience that was not evidently true.
when someone says, he knows from experience that the air is heavy, then it is not obvious for everyone what perception he has had when he recognizes the heaviness of air. It is therefore necessary that he refer to a specific case in which he recognized the heaviness of air, as for instance, that he carefully emptied the air out of a very big glass container or a copper globe, with help of an air pump, whereupon he hung it on the very long arm of a scale, after which it indicated a big difference in weight. Although this signifies the actual experience, the proposition "the air is heavy" can be concluded from it (Wolff, 1978, pp. 181-182, §. 3). 7 Underlying this particular example was the further distinction between common and hidden historical knowledge. Whereas common facts require "only attention and, of course, some acumen … hidden facts must be brought to light by skilled investigators, and even then they are not known unless reason gives its assistance to the senses. As a result we distinguish between common and secret historical knowledge" (Wolff, 1963, p. 12;Wolff, 1983a, p. 10, §. 21). 8 This distinction corresponded with that between observations and experiments.
"Observation is experience, that is centred around the facts of nature, obtained without our intervention.
Experiment is experience, that is centred around the facts of nature, which cannot be obtained without our intervention" (Wolff, 1968, p. 357, §. 456). 9 Although the terms had varied in meaning since the Middle Ages, in Wolff's time the above sense was firmly established and commonly accepted in the scientific community (Daston, 2011, p. 86;Park, 2011;Pomata, 2011). Wolff, who had taught on and written about experimental philosophy since 1709, was of course familiar with it (École, 1979;Mühlpfordt, 1992;Vanzo, 2015;Wolff, 1980a, p. 146). What I wish to bring to light here, however, is the epistemic logic of the experimental experience. Since hidden historical facts were not evidently true, it was necessary to find another way of rendering them credible or even indubitable. In the seminal study Leviathan and the Air-Pump Steven Shapin and Simon Schaffer show how this problem was solved by using a combination of material, literary and social technologies for observing, documenting, and communicating new facts to the larger community (Shapin & Schaffer, 1985, pp. 25-79). To the more specific epistemic techniques was added the replication of experiments, each of which should be rigorously documented and attended by reliable witnesses (Shapin & Schaffer, 1985, p. 60). Experiments thus conducted could reveal new, hitherto concealed truths of nature. As Dear aptly writes, it "could not be evident, but it could provide evidence" (Dear, 1995, p. 25). Wolff, who frequently referred both to Robert Boyle's emblematic experiments with the air pump and to the work of Robert Hooke, was of course well acquainted with the epistemic techniques of the experiment. 10 In the German Logic he thus recommended that everyone who wants to be wise from experience should carefully write down all his experiences that do not occur daily, and diligently examine them according to all their circumstances. Particularly if we have brought things together in nature to our liking which otherwise would not come together, that is, if we experiment, we can assure ourselves all the more that we have most carefully accounted for all the conditions under which something happens when we repeat our experiment at another time, or if we have others repeat it (Wolff, 1978, pp. 187-188, §. 12). 11 Diligent examination, documentation, and replication were thus crucial in cases where experiments were used to reveal the hidden phenomena of nature. Rather than being epistemically opposed to the evidently true experience, however, the experiment merely provided a different technology for establishing universal truths of nature. But how did the experimental logic apply to psychology? How could the soul be subjected to experimentation? When it comes to these questions we are left with a number of rather ambiguous remarks in which Wolff, for instance, proclaimed "that empirical psychology is similar to experimental physics. For it is also the case that experimental physics supplies principles for dogmatic physics" (Wolff, 1968, p. 3, §. 4, Wolff, 1980b 12 and that "there is room for it [the experiment] in all forms of philosophy, even in natural theology" (Wolff, 1968, p. 358, §. 459). 13 In spite of these bold proclamations, however, Wolff did not indicate whether he had in mind specifically psychological experiments or whether he meant rather that all sciences could benefit from, and use in demonstrations, the truths of experimental philosophy. If he had the former in mind, then the absence of RYDBERG | 387 examples of specific psychological experiments may indicate that he was simply unable to figure out what such experiments might look like or be feasible in practice. If he instead meant that there are no specific psychological experiments, however, then there are also no specific problems beyond those that apply to experimentation more generally.
Wolff's notoriously ambiguous remarks did not stop his followers from delving into the matter. The key issue was how to fulfil the criterion of intervention in the course of nature; that is, the very distinguishing feature of an experiment. Various authors came up with a number of disparate approaches. One rare but fascinating example is the Wolffian philosopher Gottlieb Friedrich Hagen, who suggested that behavioral intervention would do and that, for instance, people's abilities to memorize narrated facts would serve as a measure of attention (Ramul, 1960;Rydberg, 2021). A more common strategy was to propose surgical interventions and the measurement of nerve liquids (Nowitzki, 2003;Rydberg, 2021;Zelle, 2001a). A third possibility was that self-examinations provided a form of introspective experiment on the soul (Rydberg, 2021). What these three radically different solutions illustrate is that there was little consensus regarding the specific nature of experiments on the soul.
Within the context of this rather marginal discourse a new, and at first glance rather odd, epistemic logic came into play. Johann Gottlob Krüger studied philosophy and medicine with Wolff and Friedrich Hoffmann before he himself became a doctor of medicine in 1742 (Nowitzki, 2003;Sturm, 2010). Inspired by the iatromechanical medicine of his time, he presented exactly the kind of body-soul theory that might seem to lend itself to surgical experiments on the mind (Heinz, 1996;Nowitzki, 2003;Rydberg, 2021;Zelle, 2001a). However, in the following decade he partly abandoned this project in favor of a new strand of psychology presented in the extensive Attempt at an Experimental Psychology (Versuch einer Experimental-Seelenlehre, 1756) (Heinz, 1996, p. 27;Nowitzki, 2003, p. 76). In the very first paragraph Krüger pinpointed the crux of the problem of psychological experiments.
One would maybe take it for a mere joke if I were to say that I have taken on the task of showing how one can know the soul through experiments. Experiment, one would say, can only be conducted on bodies. Would one really bring the soul under the air-pump, observing its gestalt through the magnifying glass, measuring its powers? This thought is so obvious that I think it would occur to most people who would face these pages (Krüger, 1756b, p. 1, §. 1). 14 Having addressed the core problem of intervention, Krüger dismissed surgical interventions on living humans on ethical grounds. He then touched on the limited value of experiments on animals before arriving at a somewhat unexpected solution.
Thus, except that one can conduct many experiments on animals, the observations of medical science, made in all times, provide circumstances where the soul, through extraordinary changes of the body, is placed in such extraordinary and rare states that they quite reasonably can be regarded as experiments conducted on the soul (Krüger, 1756b, p. 20, §. 7). 15 Krüger's attempt to satisfy the criterion of intervention by appealing to documentation of extraordinary medical cases has caught the interest of several scholars. While Hans-Peter Nowitzki has noticed that Krüger did indeed rely on a large and diverse body of cases, Carsten Zelle has argued that "Krüger abandons 'experiment' in favour of 'observation' and thus upgrades descriptions of medical cases" (Zelle, 2001a, pp. 100-101). More recently, scholars have suggested that Krüger's turn to medical cases should be understood in relation to what the historian Gianna Pomata has referred to as an epistemic genre Retzlaff, 2018). According to Pomata, in the early modern age collections (historia morbi/observationes/curationes) of medical cases (casus/ exempla) constituted an established epistemic genre in the sense of "a framework for gathering, describing and organizing the raw materials of experience" (Pomata, 2010, p. 197). In this sense, they served as a systematic extension of the physician's own memory, helping him to identify diseases, causes, and cures. While it is now fairly accepted that Krüger relied heavily on this genre, I would like to add that it provided the very epistemic rationale for his claim that extraordinary cases can also be regarded as a form of experiment. Since nature had already intervened it was not necessary to make actual interventions. Collections of documented cases could hereby take the place of spatially and temporally specific experimental situations. The only thing one needed to do was thus to interpret and draw conclusions from nature's own experiments.
Krüger's suggestion was indeed innovative. Yet perhaps the most important part was not the turn to cases as such, but rather his compilation of a vast collection of medical cases, varying in length from a few sentences to several pages, covering everything from the mental effects of various physical injuries or of passionate feelings of love, hatred, and fear, to cases of people with delusions, hypochondria, and imaginary illnesses. One case thus describes a girl who recovered from a head injury after parts of her brain had been removed; another a young woman who fell into convulsions and died after having been frightened during a walk; another a young man convinced that he had a living frog in his stomach; another a mad barbarian prince who bit off and ate his own limbs; and another a young man who lost both sense and taste, and so on and so forth (Krüger, 1756a, pp. 33-34, 52-56, 73-74). Although cases such as these had figured within medicine for a long time, Krüger now adopted, adapted, and applied them within psychology. 16

| EXTRAORDINARY CASES AND PSYCHOLOGICAL CASE HISTORIES
Although the path from Krüger to a more expansive empirical psychology is not clear-cut, in retrospect there can hardly be any doubt that a case-based psychology belonged to the future. In Concise Conception of all Science (Kurzer Begriff aller Wissenschaften, 1759) the mathematician and philosopher Johann Georg Sulzer thus stressed that "it would also be very useful if some extraordinary psychological cases, which cannot yet be explained through the known properties of the soul, were studied in detail in specific contributions" (Sulzer, 1759, p. 159, §. 207). 17 Yet, despite Sulzer's optimistic remark, the actual breakthrough would not come until the early 1780s. In 1782 the philosopher and writer Karl Philipp Moritz published a text titled Prospect of an Experimental Psychology (Aussichen zu einer Experimentalseelenlehre), in which he advocated for the necessity of a journal of experimental psychology. In a manner strongly reminiscent of Krüger's approach he argued that "from the combined reports of several scrupulous observers of the human heart could an experimental psychology emerge, which practical utility would exceed everything that our ancestors have achieved in this field" (Moritz, 1782a, p. 6). 18 In the same year as Prospect was published it was also reprinted under the title Proposal for a Journal in Empirical Psychology (Vorschlag zu einem Magazin einer Erfahrungs-Seelenkunde), with a revised introduction in which Moritz remarked that "Mr Moses Mendelssohn has himself shared with me his thoughts about the plan of this study, and he gave me the advice to change the name experimental psychology, which I had chosen from the beginning, into empirical psychology" (Moritz, 1782b, p. 503). 19 The following year the journal appeared as Know Thyself or Journal of Empirical Psychology (ΓΝΩΘΙ ΣΑΥΤΟΝ oder Magazin zur Erfahrungsseelenkunde, 1783-1793). The anecdotal detail of how Moritz changed the title is, as Zelle has remarked, indicative of the larger process through which experimental psychology was abandoned for empirical psychology (Zelle, 2001a). A few years later this development was further cemented through Immanuel Kant's famous critique of psychology in Metaphysical Foundations of Natural Science (Metaphysische Anfangsgründe der Naturwissenschaft, 1786) (Hatfield, 2006;Kraus, 2020;Sturm, 2006Sturm, , 2009).
According to Kant, empirical psychology can "never approach chemistry even as a systematic art of analysis or experimental doctrine, for in it the manifold of inner observation can be separated only by mere division in thought, RYDBERG | 389 and cannot then be held separate and recombined at will" (Kant, 2002;4:471). As a result, it can "never become anything more than an historical doctrine of nature, and, as such, a natural doctrine of inner sense which is as systematic as possible, that is, a natural description of the soul, but never a science of the soul, nor even, indeed, an experimental psychological doctrine" (Kant, 2002;4:471). Although Kant's verdict dealt a heavy blow to any claim to an experimental psychology, it did not, as we will see, put an end to the attempt to launch empirical psychology as a form of science.
Moritz's journal Know Thyself or Journal of Empirical Psychology featured a large collection of cases, divided into the two major categories of "pathology" (Seelenkranheitskunde) and "physiology" (Seelennaturkunde). 20 Whereas the former focused on the kind of extraordinary cases that we have already seen in Krüger, the latter was more complex, as it incorporated a broad range of sources, including biographical and autobiographical accounts, letters, diaries and detailed observations and self-observations. The inclusion of these sources represented a clear expansion of the epistemic genre of medical case collections. Most importantly, by accounting for people's lives, including everything from their earliest childhood memories to particularly traumatic events or mundane thoughts and feelings, psychology became a matter of exploring the human soul, not as a rigid and universal structure, but as a vast and open-ended field of human experience. This interest in the human being as a complex whole, where body and soul are intimately connected and constantly in interaction, reflected what scholars have referred to as the anthropological turn (Borchers, 2011;Geyer-Kordesch, 2000;Heinz, 1996;Košenina, 2009;Nowitzki, 2003;Sträter & Lehmann, 2009;Zelle, 2001b). Starting around midcentury, the anthropological turn featured a broad interdisciplinary and highly eclectic exploration of the medical, physiological, psychological and moral aspects of human existence. In the second half of the century, the anthropological turn fed into and fused with the culture of sensibility as well as the broader interest in subjectivity and selfhood of which it was part. 21 That the expansive usage of cases that Moritz's journal exemplifies reflects a broad social, cultural and intellectual interest in the unique individual experience is today fairly accepted among scholars (Fossaluzza, 2006;Košenina, 2009;. Most notably, Leventhal has remarked that it is in this broader context that the narrative psychological case history emerged as a unique attempt "to articulate the individual in its very individuality-a unique self, conceived in its irreducible singularity" (Leventhal, 2019, p. 1).
The expansion of the category of cases to include letters, autobiographical reflections, observations of other people, and self-observations was a clever way of appealing to a broad spectrum of readers and contributors. One who was "passionately captivated" by the journal was the theologian and writer Immanuel David Mauchart, who Materialen-Sammlung zur künftigen Aufklärung in der Erfahrungs-Seelenlehre, 1789) (Mauchart, 1789a;preface). 22 In the Appendix Mauchart remarked that if only enough material could be collected and analyzed the reader would understand "that the result follows as necessary from the connected observations as 5 from 2 × 2 + 1" (Mauchart, 1789a;preface). 23 Similarly, in Phenomena of the Human Soul he emphasized that his intention was not to challenge Moritz's journal or even to produce scientific truths but rather to collect and offer material for others to analyze (Mauchart, 1789b;preface). That Mauchart explicitly described his endeavor in this way is indicative of the new case-based psychology in which the mere collection of material was seen as a fully sufficient contribution.
From an epistemic point of view the promotion of a new empirical psychology based on various forms of more or less extraordinary cases marked an important shift from the kind of baroque psychology that Wolff represented to a more "phenomenological" psychology in which the level of individual experience was layered onto the traditional discourses of the different faculties. Whereas for Wolff, who was interested in the universal and general, it would have made little sense to dwell on individual cases or to compose extensive case collections, Moritz saw such material as pivotal to the exploration of the inexhaustible field of individual and subjective human experience.
Rather than just adopting the classical medical case or even the extraordinary case of Krüger, however, Moritz's journal featured the active production of a broad spectrum of eclectic, partly medical and partly literary cases, some of which extended into book-length psychological case histories. Clearly the most striking example is Moritz's own four-volume autobiographical novel Anton Reiser: A Psychological Novel (Anton Reiser. Ein Psychologischer Roman, 1785-90). The work accounted for Reiser's life from early childhood to adulthood (Fossaluzza, 2006;Košenina, 2009). Deeply influenced by the culture of sensibility, Reiser's life unfolded as a struggle between periods of exaggerated feeling and attempts to control its forces through reason and the intellect. Although Reiser sought to discipline himself through diary writing, it was only after much training that he was eventually able to observe his own behavior.
At that time, Reiser did not yet know how to observe the influence of external-real events on the inner state of his mind; his attention to himself had not yet received the proper direction. However, his diary improved over time, in that he began to record not only the events, but also his intentions and resolutions, to eventually see what he would have achieved.-He thus made laws for himself, which he wrote down in his diary to bring them to fruition.-He also occasionally made solemn vows to himself, e.g., to get up early, to divide the hours of the day, and the like (Moritz, 1786, p. 15). 24 Seen in relation to the journal, the novel might be said to provide one lengthy and exemplary psychological case study. That the two were intimately interwoven is also suggested by the fact that extracts of the novel were published as particularly revealing cases in the journal. In volume 2, a fragment thus appeared, recounting how Reiser had developed a preference for sensibility as a child.
Thus his imagination was responsible for most of his childhood sorrows and joys. How often, when on a dull day he was locked up fastidious and disgusted in the room, and a ray of sunshine fell through a windowpane, suddenly he was awakened by ideas of Paradise, of Elysium, or of the island of Calypso, which made him feel delighted for hours (Moritz, 1784, part. I, p. 78). 25 Anton Reiser reappeared every now and then, and in volume 8 a long excerpt was published, again containing detailed observations regarding Reiser's fluctuating inner life.
The annoyance which then took the place of the tickled hope was of such a coarse, mean, and repugnant kind that not even the slightest degree of mild melancholy or anything like that could exist with it. It was almost like the feeling of a person who is soaked through by the rain, and when he returns home shivering from the frost, he also finds a cold room (Moritz, 1791, part. II, p. 24). 26 These passages exemplify how observations and self-observations often unfolded as detailed narratives of intense sensibility. The lack of clear distinctions between brief cases and volume-length literary accounts was not unique to Moritz. A particularly revealing example here is the Swiss poet, philosopher and theologian Johann Caspar Lavater. Lavater is most famous for his physiognomy, in which he sought to extract information regarding people's inner lives by studying their external appearance, gestures and general behavior. Before launching physiognomy, however, Lavater published A Secret Diary of a Self-Observer (Geheimes Tagebuch von einem Beobachter seiner Selbst, 1771), followed by the sequel Unchanged Fragments of the Secret Diary of a Self-Observer (Unveränderte Fragmente aus dem Tagebuche eines Beobachters seiner Selbst, 1773). In the preface to the first volume Lavater stressed that the aim was to contribute to the history of the human heart by providing a detailed account of his daily struggle to structure life around Christian principles and spiritual exercises. Having set up a list of 12 rules of Christian virtue (start and end every day with prayer, read the Bible, etc.), the work then proceeded by documenting successes as well as failures (Lavater, 1771). Two years later the Unchanged Fragments appeared, and in the preface Lavater admitted that the first volume had been edited and that now, at readers' request, he wanted to display the source RYDBERG | 391 text unaltered. Although it is questionable whether the second volume actually consisted of such unaltered fragments, some observations display a clear focus on the inner life.
When I woke up, I considered and examined the previous day. I scrutinized all situations in my imagination.
How often did I have reason to blush! How completely different we see and judge ourselves if we only look at ourselves with the eyes of an impartial witness. With this in mind, I wished to have more time and skill in drawing to be able to fix by means of drawings many situations in my life that can hardly be described in words…. What if I saw someone else doing what I am doing now? Someone who thinks the way I think I am now, looking into the soul? If I saved this situation with a drawing how would I then appear in those quiet hours when passion is silent? (Lavater, 1773, pp. 197-198) Although an extreme example, it nevertheless illuminates the pivotal role of self-observations in empirical psychology.
Far from the Wolffian attempt to demonstrate what generally and universally pertains to the soul, we here face a kind of fragmentary jotting that attempts to capture and summarize the daily stream of thoughts and emotions. More than rational demonstrations, they bring to mind a physician who meticulously observes every instance of change in the diseased body or the experimental philosopher who accounts for every minor occurrence during an experiment.
To summarize, in the second half of the eighteenth century and especially from the 1780s onward the use of medical cases within empirical psychology expanded to include not only extraordinary cases extracted from existing literature but also the active production of a broad spectrum of cases stretching from biographical and autobiographical accounts to diaries, letters and specific observations and self-observations. While the cases presented in Moritz's journal were typically not longer than a few pages, there was no limit to how extensive they could be-as illustrated both by Moritz's psychological novel Anton Reiser and by Lavater's A Secret Diary of a Self-Observer. What for Wolff had been a matter of defining and drawing conclusions from common knowledge of the soul, now seemed to take the form of an open-ended exploration of human subjective experience as such. For Moritz and Lavater there was no outer limit to the individual web of thoughts, imaginations and emotions. Although they would have agreed with both the Wolffians and the physicians who sought patterns, structures and principles, this new empirical psychology was first of all a matter of collecting and exploring vast amounts of data.

| DEVELOPING A SYSTEMATIC METHOD FOR OBSERVATIONS AND SELF-OBSERVATIONS
So far, we have seen how empirical psychology underwent a thoroughgoing epistemic transformation from the mideighteenth century onward. Where it had before relied on evidently true experience of how the mind generally works, it later adopted extraordinary cases from medicine as the backbone of a psychology oriented toward individual differences and, particularly, abnormality. From around the 1780s the use of cases expanded to include a variety of materials, from fragmentary observations and self-observations to volume-length psychological case histories. It is significant that cases were no longer simply extracted from established literature but also actively produced. The production of cases went hand in hand with a rapidly expanding methodological discourse on observations and particularly self-observations. The research on this material is surprisingly sparse. While some texts have been discussed, for instance, by Fernando Vidal, Thomas Sturm and Gary Hatfield, the focus is typically on the different subdisciplines and methods of psychology (empirical, rational and transcendental psychology) rather than on epistemic logics (Hatfield, 2006;Sturm, 2009;Vidal, 2011).  (Sturm, 2006(Sturm, , 2009Vidal, 2011).
Most importantly, Schütz addressed a predicament that would haunt empirical psychology for the rest of the century. "The spectacle presented by the human soul is so varied, so composed; and who is now the spectator of it?
She herself is both an actor and a spectator; a circumstance which causes the greatest difficulty in psychology" (Schütz, 1771, p. 192). 29 Not only is the soul simultaneously an observing subject and observed object, but in both these roles it "resembles a fast-flowing stream that always seems to stay the same, and yet is always changing" (Schütz, 1771, p. 203). 30 Given these conditions, the epistemic techniques developed within experimental philosophy might appear difficult or even impossible to apply to the soul. However, for Schütz this very predicament rather seemed to call for their extraordinarily rigorous application. Here he stressed three methodological principles. First, "one must collect a great number of individual observations before one can deduce a certain result from them, and never forget that the incidents which one observes are individual cases, from which the general can be inferred only with great care and caution" (Schütz, 1771, p. 264). 31 Second, "one must rather notice the phenomena of the soul with all their ancillary features than tearing them out of context, where they often get a completely different appearance. Without observing this rule, it is often impossible to get out of apparent contradictions" (Schütz, 1771, p. 265). 32 And third, "one must not ignore trifles and accidental manifestations, no matter how minor they may appear" (Schütz, 1771, p. 265). 33 Schütz's discourse evinces a significant epistemic transformation. First, in sharp contrast to the Wolffian and most other strands of early modern psychology, the aim was no longer to establish general truths about the soul by adducing evidently true empirical propositions. Instead, Schütz resorted to the epistemic logic and techniques of experimental philosophy, in which singular observations were accumulated and systematically analyzed. Second, Schütz's discourse also differed from that of the extraordinary medical case. Although cases ultimately relied on actual observations, in their collected form they typically became spatially and temporally detached from their originating circumstances. Schütz's method, in contrast, instead took the form of a detailed instruction in the actual practice of self-observation.
Schütz's attempt to apply the epistemic techniques of the experimental experience to self-observation was an early example of a discourse that proliferated in the last decades of the century. A second example can be found in the work of the philosopher Johannes Nikolaus Tetens, who came up with similar suggestions in the preface to Philosophical Inquiries into Human Nature and Its Development (Philosophische Versuche über die menschliche Natur und ihre Entwicklung, 1777).
Notice the modifications of the soul as they appear through self-reflection; repeat, observe and perceive these under different circumstances, notice the way they emerge and the laws of operation of the forces that they produce; then compare and resolve the observations, and from these try to discover the most elementary abilities and effects as well as their relations to one another. These are RYDBERG | 393 the most essential performances in the psychological analysis of the soul, which is based on experience. This method is the method of natural philosophy (Tetens, 1777;preface, p. 4). 34 Like Schütz, Tetens spotlighted a number of difficulties connected to the constantly fluctuating nature of the mind. To compensate for this predicament, which pertained to the mind as observer and as object of observation, Tetens advocated the accumulation of numerous observations. "I know no means effective enough to guard against these [the delusions of the inner senses], other than the repetition of the same observation, both under similar and different circumstances, each time made with the firm determination to distinguish and strongly acknowledge what is real perception from what is added fantasy" (Tetens, 1777;preface, p. 17). 35 In addition to discussing the method of self-observation, Tetens also stressed the importance of extracting principles out of these. "One of the most noble operations in the observational method consists in turning the particular empirical propositions drawn from individual cases into general propositions" (Tetens, 1777;preface, p. 19), 36 by means of analogy. "In the end," Tetens remarked, "it is the reflections and conclusions that make the simple observations really useful, and without which we would have to remain constantly only on the outer surface of things" (Tetens, 1777;preface, p. 30). 37 In the following decades the discourse on methods within empirical psychology was further elaborated by several intellectuals. One case in point is Johann Werner Streithorst, who despite his profession as a theologian entertained a special interest in psychology. In Psychological Lectures (Psychologische Vorlesungen, 1787) he provided a detailed discussion of self-observation. In line with his predecessors, Streithorst stressed the necessity of rigorously conducted self-observations.
Only attentive, conscious, sustained and repeated perception, encompassing the object from all sides, deserves the name observation, and only the one deserves the name observer who already has the skill and the predominating tendency to perceive in the way described. Attention and adhesion to the object of observation, lengthy consideration of the same and frequent repetition of this operation of the soul thus constitutes the essence of self-observation (Streithorst, 1787, p. 8). 38 If the observer of nature might easily be misled by the external senses, the challenge of the self-observer is even greater because the mind is a constantly changing subject and object. For this reason, it was particularly important to conduct numerous observations. "Moreover, one must only repeat the same observation once with the same accuracy to convince oneself that one does not exhaust an object at once. Even after repeating the same observation for a thousandth time, there is still something left to discover" (Streithorst, 1787, p. 17). 39 The selfobserver must procced in the same manner as the natural philosopher who observes the sky through the telescope or a drop of water through the magnifying glass and then systematizes the observations. "He compares present appearances of his soul with former ones, distinguishes the rare from the ordinary, and like the natural philosopher he has his own cabinet of curiosity where he particularly notices the rarities and brings everything into its class and order" (Streithorst, 1787, p. 14). 40 Around 1790 empirical psychology had risen to become a new fashion of the day. One of those who sailed with the wind was the philosopher and writer Ludwig Heinrich Jakob, who published the Outline of Empirical Psychology in 1791 (Grundriß der Erfahrungs-Seelenlehre). The Outline, which was published in four editions (1791, 1795, 1800, and 1810), contained a substantial discussion of method. On the one hand, Jakob drew on Kant when comparing empirical psychology to physics and chemistry. "Hence the method in psychology is the same as in physics and chemistry. Everything must be explained from other phenomena; and metaphysical assertions and transcendental hypotheses are the true qualitates occultae" (Jakob, 1791, p. 2, §. 3). 41 On the other hand, he clearly drew different conclusions as regards the possibility of experiments on the soul. "First one collects a variety of individual effects through observation and experiments, and by comparing them one seeks the known general laws of experience, to discover the general rules, which serve to explain past and future phenomena" (Jakob, 1791, pp. 2-3,  §. 3). 42 Jakob here boldly claims that empirical psychology does indeed proceed in the same way as physics. While this is a rare exception to the tendency to dismiss the use of experiments in psychology, one must not forget that the use of epistemic techniques adopted from experimental philosophy was well established in the early 1790s. The difficulties that Jakob highlighted were basically those that had been recognized for about two decades. Hence, Jakob argued that mental phenomena are problematic objects of study because of (1) their changeability and low durability, (2) the difficulty of conducting and repeating experiments, (3) the difficulty of staying focused during selfobservations, (4) the great number of variable phenomena, of which some are important and others not, (5) the lack of available critically collected and examined data, and (6) the unreliability of other people's observations (Jakob, 1791, pp. 3-4, §. 4). These difficulties, Jakob continued, are certainly important explanations for the slow development of empirical psychology as a science.
Jakob belonged to the same circle as Carl Christian Erhard Schmid, who had established himself as one of the leading representatives for early Kantianism in the 1780s. In 1791 he published the voluminous Introduction to Empirical Psychology (Einleitung zür Empirischen Psychologie) (van Zantwijk, 2010). Schmid's psychology provided detailed instructions on what to observe, how to conduct observations and how to process the collected data (Schmid, 1791, p. 103, §. 15). He expanded on earlier methods to consider not only inner states and their changes but also physiognomy, behavior and even creative products such as art and literature. To become a skilled observer required "a talent of one's own, for lively and subtle sensation and distinct perception of the inner sense and for abstraction from the outside world" (Schmid, 1791, p. 108, §. 21). 43 Further requirements included "freedom from preconceived notions of the human soul," "exercise in observation in general," "acquaintance with the object of study," and "knowledge of the special circumstances which obstruct the business of spiritual observations" (Schmid, 1791, pp. 108-109, §. 21). 44 As for these "special circumstances" Schmid was aligned with his predecessors when stressing difficulties such as the "amount of things to be observed," "diversity of things," "continuity of things," "ceaseless flow and change," "confusion and obscurity," "imperceptible detail," "impossibility of a mathematical representation," and "impossibility of real examination and deliberate experiments" (Schmid, 1791, pp. 110-114, §. 22). 45 To these were added a number of other difficulties connected to the ways in which the act of observation impacts that which is being observed. To remedy these problems Schmid came up with a list of 12 rules. The observer should (1) "pay attention to details," (2) "not despise the every-day and common," (3) thoroughly analyze the effects of known faculties of the soul, (4) prioritize thorough observations over "superficial, carelessly collected, indefinite" ones, (5) neutralize the negative influence of "common and personal prejudices or the impact of inclinations and passions on the observation," (6) not let some expected result "come in the way of the continued observation, or destroy its impartiality," (7) be led but not controlled by analogies, (8) make broad explorations and investigations rather than narrow ones, (9) "record his observations in writing and keep them in a properly laid out and organized psychological journal," (10) not confuse facts with explanations of these, (11) communicate and discuss results, and (12) take into account psychological writings as well as biographies and observations (Schmid, 1791, pp. 120-126, §. 23). 46 To fulfil the purpose of establishing "psychology as science", collected data had to be processed and refined into scientific truths (Schmid, 1791, p. 126, §. 24). 47 First, it was important "to discover general empirical concepts and empirical rules that can be subsumed under the pure laws of nature" (Schmid, 1791, p. 126, §. 24). 48 Then one should "generalize these rules and concepts more and more, order and subordinate them in relation to each other, and ascend to the basic forces and the basic laws of the mind" (Schmid, 1791, pp. 126-127, §. 24). 49 By doing so one contributes to the unity of psychology as a systematic science. For those interested in further advice regarding the collection and processing of data, Schmid recommended the reading of none other than Schütz's Reflections, Moritz's Prospect and Streithorst's Psychological Lectures (Schmid, 1791, p. 128, §. 24). That Schmid referred to these works is typical and bears witness to the existence of a scientific community of psychologically oriented intellectuals.
A few years later Schmid would have the chance to apply some of his principles in his own Psychological Journal (Psychologisches Magazin, 1796-98). While remarking that it was important to fill the gap left when Moritz's journal had ceased publication, Schmid stressed that his journal sought not only to establish "raw material" but also "to RYDBERG | 395 present examinations, to classify the present material under general concepts and to set up natural laws of the greatest possible generality, definiteness, systematic connection and evident certainty" (Schmid, 1796;preface). 50 In structuring the journal around general concepts and rules, rather than cases, Schmid was true to his own understanding of empirical psychology as a systematic science. In this respect the journal represents a step back to the kind of systematic psychology that was introduced already by Wolff.
To summarize, beginning in the early 1770s intellectuals developed an extensive discourse on empirical methods in psychology. In doing this they adopted the epistemic techniques for accumulating evidence by conducting and documenting numerous singular observations, on a model similar to experimental philosophy. The difficulties associated with the study of the soul were not seen as an argument against these techniques but rather seemed to call for their rigorous and systematic application. Hence, the observer of the soul must be even better prepared than the observer of nature. Although self-observations differed from medical cases in terms of epistemic techniques, once conducted they were typically presented in a similar format. That is, self-observations were refined into cases that, once gathered in large collections, were expected to reveal more general and complex truths. These distinct epistemic logics were thus not opposed, but provided different and typically complementary techniques for arriving at general and universal truths of the soul.

| CONCLUSION
This article draws on recent attempts to historicize basic epistemic categories such as truth, fact, experience, objectivity and the like. It uses the concept of epistemic logics to capture both the basic assumptions and criteria regarding what counts as scientific knowledge and the specific rules, procedures and practices through which such knowledge becomes intelligible. Previous studies of 18th-century psychology have focused on the overall discipline as well as on its various parts, theories and methods; the analysis of epistemic logics provides an important dimension to our understanding of the many disparate attempts to acquire empirical knowledge of the soul by charting the very basis of its intelligibility.
Three different yet compatible epistemic logics operated in this context. The first was that of the Aristotelianscholastic experience, which was typically used to form universal and evidently true propositions of how things generally behave in nature. While trivial in themselves, universal empirical propositions could nevertheless be used to demonstrate more complex truths. When Wolff launched empirical psychology, it was this logic that fueled the attempt to establish the general nature, structure and functions of the soul. From midcentury, a new generation of physician-philosophers launched a brand of empirical psychology based on extraordinary medical cases. Whereas the Wolffian psychology charted the general and universal, the case-based psychology was oriented toward the vast and open-ended field of human experience. As a part of this broad focus, the margins of human experience, the deviant and abnormal, became of central concern. From the early 1770s this interest was complemented by a new methodological discourse, in which epistemic techniques rooted in experimental philosophy were adopted and applied to psychological observations and self-observations. Observers were to be disciplined and well trained in systematic observations and self-observations, as well as in how to document and process these into scientific knowledge.
The elaboration of psychological observations and self-observations is fascinating but also intriguing. Within experimental philosophy new epistemic techniques were developed as a result of new technologies that gave access to hitherto hidden phenomena of nature. It was necessary to observe and document exactly what happened in an experiment with the air-pump to establish facts that could otherwise easily be doubted. In empirical psychology there seem to have been no such new technologies. This, in turn, makes one wonder whether the new epistemic techniques served a merely rhetorical function in rendering empirical psychology scientifically credible.
While there is probably some truth to the claim, this does not mean that there were no systematic selfobservations. Quite the contrary, it seems to me that these techniques were adopted in a situation where detailed self-observations already figured as a part of the culture of sensibility. If this interpretation is correct, it means that they served to systematize and articulate an existing practice that figured in a variety of contexts that were often cultural and literary rather than scientific. Such an interpretation is aligned with the view of empirical psychology as a deeply heterogeneous endeavor. Whereas the Wolffian psychology was almost exclusively a matter for philosophers, in the empirical psychology that took form in the wake of the anthropological turn, philosophers, physicians, theologians, poets and writersmost of whom knew and referred to each other-charted the human soul in different genres such as novels, autobiographies, diaries, journals, textbooks and extensive academic treatises. In this sense, the second half of the century witnessed the emergence of a highly eclectic scientific community.

ACKNOWLEDGMENTS
This study would not have been possible without insightful feedback from colleagues at the Department of History of Science and Ideas at Uppsala University. I also wish to thank two anonymous reviewers for valuable suggestions and criticism. This study was supported by the Swedish Research Council (Ref: 2018-01187).

DATA AVAILABILITY STATEMENT
No data have been collected for this study.