system
Given the following post, respond as if you're commenting on Reddit:
human
Who are some significant "pantheist" philosophers other than Spinoza who believed essentially that 'matter/energy' and 'spirit' are the same phenomena/completely identical, thus implying that the universe was not created by an eternal being, but is in fact an eternal being?
gpt
Spinoza thinks that matter and mind are two different attributes of substance, which is a neutral monist position and at odds with the idea that they are "the same phenomena/completely identical."  What it suggests is that matter and mind are two different expressions of, or two different ways of conceiving a single underlying substance.  Accordingly, they have a kind of unity to them, insofar as they are both expressions of the same substance, and this has theoretical consequences, notably in the notion of a strict parallelism between mental events and material events.  But mind and matter also have an irreducible diversity in Spinoza's philosophy, since while they are about the same substance, they are nonetheless still fundamentally different in their expression of it.  This too has consequences, namely the mutually irreducibility of mind and matter, and the strict independence of the causal history of each.

But none of this really has anything obvious to do with whether the universe was created by an eternal being or whether the universe is in fact an eternal being.

Spinoza's account of the relation between God and nature is, *for a large part*, fairly traditional: he understands God to be an infinite, eternal, immutable, self-caused, omnipotent and maximally free substance whose creative activity produces nature, and he distinguishes being regarded as this infinite substance, which he calls "naturing nature" (in the sense of nature that is enacting the process of naturing), from being regarded as the product of the creative activity of this substance, which he calls "natured nature" (in the sense of nature that results from the process of naturing).  So far this is pretty typical stuff for the tradition of metaphysics which runs from ancient philosophy to the rationalists.

Where Spinoza departs from the orthodox Christian understanding of this metaphysical picture is with two related points.  First, he thinks that God's omnipotence and freedom only make sense if it's recognized that God's creation of everything he *could* create necessarily follows from them.  That is, he thinks that if God would ever *not* create something, that there must be something which held him back from doing so, but in that case he wouldn't be omnipotent and maximally free, so that God's omnipotence and maximal freedom, somewhat ironically, render the creative act a metaphysical necessity.  Traditional theology had often wanted to identify a point of contingency here, to imagine that God could have chosen to create or not, and accordingly to understand creation as a contingent and freely willed event.  For Spinoza, conversely, creation follows necessarily from God's nature.

The second radical point of Spinoza's philosophy follows from this.  Just as the traditional theological picture tended to conceive the creative act as contingent, it also tended to conceive of *its object* as contingent.  That is, God could freely choose to create or not to create, and he could also freely choose to create one possible universe rather than some other one.  Spinoza, conversely, argues that God's omnipotence and freedom only make sense if his creative activity is expressed without limitation.  That means not only that the creative act necessarily follows from God's nature, it also means that God, as it were, *doesn't hold himself back* so as to make one particular sort of universe (i.e. typically, in the theological picture, one particularly kind to human beings) but rather just limitlessly creates an infinite diversity of everything that can be created.

Spinoza, then, might be called a pantheist because in his philosophy (i) God and creation are not separated by a notional point of contingency, but rather are more closely connected, through the *necessity* of the creative act, than in the orthodox theological picture, and (ii) there is similarly no notional space between the various possible universes and the one God chose (providentially) to create, but rather creation expresses God's infinite nature in its own limitlessness--limited not even by a providential design.  In these two ways, Spinoza's God is, as it were, *closer* to creation than in the orthodox picture.

Whether this means that "the universe was not created by an eternal being" is not clear.  The universe is, straight-forwardly, certainly created by an eternal being in Spinoza's philosophy.  But this creation is a necessary rather than contingent act, which might reasonably be regarded as an important difference from the traditional theological accounts of creation.

Similarly, is the universe "in fact an eternal being" for Spinoza?  Certainly, insofar as there is only one being (God), this being is eternal, and the universe is its expression.  But so far as this goes, it's not significantly different from the traditional theological and metaphysical picture.  What is different about Spinoza's universe is its necessary connection to God and its infinite nature rather than providential design.

The difference between Spinoza's "pantheism" and traditional "theism" is thus less straight-forward, and certainly of a different nature, than is popularly supposed.

As to what other philosophers present a metaphysical picture similar to Spinoza's on these points, as suggested above, the framework of his system is fairly traditional.  The ways I've noted above in which he departs from the traditional system are not entirely original to him, but can be found raised in medieval debates and still further back in the context of ancient philosophy.  Spinoza's own emphasis on God's freedom and omnipotence over notions of contingency and providential design are themselves claims that had already been developed in the context of Reformation critiques of Catholic theology, and Spinoza may have inherited them from this tradition of Christian thought through his contact with the Collegiants.  One can thus go back through the history of traditional metaphysics that stretches from the ancient Greeks to the early modern rationalists and find much in various sources that is sympathetic with Spinoza.  Eriugena often received the pantheist characterization, as did the Latin Averroists, and various Renaissance philosophers of nature, e.g. Bruno.  Going back to the Greeks, the pantheism characterization is leveled rather extensively: certainly at the Platonists, Stoics, and at least some of the pre-Socratics.

Of the rationalism which flourished in the early modern period, Spinoza's is particularly noteworthy for the points mentioned above, which are suggestive of the pantheist characterization he often receives, while Descartes, Malebranche, and Leibniz tended to argue the more orthodox line which recognized a greater distinction between God and creation, especially permitting a notion of providential design.  After this rationalist period, the general project of traditional metaphysics in which thinking like this--pantheist or not--occurred largely fell out of favor and was replaced first by empiricism and then by various reactions to it.  In this later period, one may wish to look particularly at Schopenhauer, who also often receives the pantheist label, and belongs to the general context of German idealism and romanticism where an interest in rationalist metaphysics and especially in Spinoza was briefly revived.