system
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human
What does Marx mean by the following passage in his Paris manuscripts of 1844?

“ If man’s feelings, passions, etc., are not merely anthropological phenomena in the narrower sense, but truly ontological affirmations of essential being of nature, and if they are only affirmed because their object exists for them as an object of sense, then it’s clear: .............only through developed industry, i.e., through the medium of private property, does the ontological essence of human passion come to be both in its totality and in its humanity; the science of man is therefore itself a product of man's establishment of himself by practical activity. The meaning of private property liberated from its estrangement is the existence of essential objects for man, both as objects of enjoyment and as objects of activity. “ 

P.S. Can someone also clarify what is the difference between ontology and metaphysics? Thanks in advance.
gpt
This passage by itself is quite dense if you are not familiar with the larger body of Karl Marx's work, particularly his earlier writings. 

In essence, he's trying to demonstrate how the concept of alienation emerges under capitalism. It also rebukes the counterargument that private property is necessarily (or essentially) a property of the human condition. It's also a good restatement of a few key themes of Marx: historical materialism, the theory of alienation, and Marx's concept of humanity (or human "being-ness"). Finally, he suggests what it would mean for mankind to exist outside of capitalism ("private property"). 

To do so, he first has to explain the importance of materialism (in a philosophical sense): that our reality (or at least our relation to it) is determined ("affirmed") by the external world ("the object"). The external world is known to us through our senses. The senses, influenced by external objects, excite within us "feelings, passions, etc." If we assume that these feelings and passions are at the root of our experience ("ontological affirmations of an essential being of nature"), then it follows that the external world of objects in some sense determines how we feel. What's being implied — and what is very important — is that the external world is contingent, or historically rooted. While the feelings themselves (how feelings make us feel) are timeless and ineffable. 

In other words: Different objects in different times or in different places can you make you feel things differently, but the feeling itself, as it is experienced, is timeless and eternal. All men know happiness and sorrow, even if they live with different objects (which determine the happiness or sorrow). 

Thus, Marx posits that if this is the case (which he has sought to prove), the way in which objects of our world *come into being* specifically in our time ("developed industry") in some sense constitute *for us* what it means for us to *be* human (for good or bad). (If objects influence our passions, then the way in which the objects come into being must also influence our passions ). 

When Marx speaks of the essential nature of man's "practical activity", he's furthering the materialist claim made earlier, advancing from a metaphysical claim to a socio-political one — and showing them to be one and the same. If objects constitute the way in which we perceive the world, then so must the way in which we act within the world of objects (i.e., the way they are produced and the way that society is constructed around this production). In other words, the way in which we occupy our times (often producing objects) determines who we are and how we interact with the world.

Importantly, he's reaffirming his definition of "mankind", or what "mankind" might mean outside of the historically constituted man — what in German he calls elsewhere *Gattungswesen,* which means "species being". 

Remember, feelings of all sorts are at the root of our experience of existence, as he proved earlier. If man is defined by what he does, then shouldn't it follow that we should be *happy* or *proud* of what we spend our time doing? 

Consider then, 

*"The meaning of private property liberated from its estrangement is the existence of essential objects for man, both as objects of enjoyment and as objects of activity."*

What he's suggesting in the final sentence is that objects exist for man in some historical contexts as fundamentally "estranged". To make sense of this, we have to consult the larger body of Marx's work:

Throughout this passage, he's implicitly forming an *ethical* or *moral* component to his argument, which we must consider when talking about any particular form of social arrangement and production, which is what Marx is hinting at here. In other words, that a particular form of social arrangement — one determined by private property — estranges man from the objects of his making. 

Lurking outside this specific excerpt is his one of his earlier critiques of capitalism: that capitalism is fundamentally *alienating* ("*Entfremdung"* is the German word used in the *1844 Philosophical and Economic Manuscripts,* which more literally means "estrangement", as used above.)

The younger Marx seems to be a bit more of the "humanist" Marx, in that he seems to suggest that there is an essential human-ness always at play within man. Because capitalism forces man to work (to labour) and produce objects not for his consumption, but for the consumption of others, there is something "unnatural" about this. 

To produce something for another's consumption which you yourself might not enjoy is not, in itself, the problem. A blacksmith who works for himself no doubt "works hard" to make a fence for another to enjoy, but he is paid for his labour upon completion. He also probably enjoys being a blacksmith, or takes some degree of pride in his work. When he's paid for his labour, his labour reaffirms itself: he can be proud in the time he spent with his practice (interacting with the material world, as discussed earlier).

However, under 19th century capitalism, this wasn't the case for most men (nor is it the case for mankind today). A man works in a factory to produce a component of a machine that not only will he never enjoy, but that he will never be paid for the full cost of his labour (this is where Marx's theory of surplus value emerges, which isn't strictly relevant to this passage). Thus, he is estranged, estranged from the moment he beings to produce an object, and forever estranged from the product of this labour that he spends his time working to produce. 

Such a man spends the majority of his waking life, from adulthood until death, always producing objects that are never "his". As a consequence, not only is he alienated from each product, but his whole life is itself alienated from his true species being because he cannot spend his time as he likes. He must isntead endlessly toil to simply survive. 

Surely this is no way to live, as it is a miserable existence (we are defined by our matieral world, recall)... 

Thus to return to the powerful conclusion of this passage:

*"The meaning of private property liberated from its estrangement is the existence of essential objects for man, both as objects of enjoyment and as objects of activity."*

He's suggesting that if we liberate mankind from private property (that is, all men as historical beings under capitalism), the external world of objects — both as physical products as well as the time spent making them — will cease to be alienating. Man will be made whole again. 

As for the difference between ontology and metaphysics, Marx means "ontology" or "ontological" to mean the way in which something (mankind, an object, etc.) is constituted (usually in the context of other things). We might say that the ontology of an individual man — you or I, say — is the feeling of being human, which itself is largely defined by our material world, which is historically constituted (that is, exists within history). 

Metaphysics is a form of philosophical enquiry that seeks to explain the relationship of things in the world to one another, us included. Marx's materialism is a metaphysical analysis of the world: external objects act upon our senses, which influence our passions. This inscribes a hierarchy between the thinking subject and the world of objects (or the external world).     

Hope that helps.