Marx

...the worker sinks to the level of commodity and becomes indeed the most wretched of commodities... (70)

But the estrangement is manifested not only in the result but in the act of production--within the producing activity itself. How would the worker come to face the product of his activity as a stranger, were it not that in the very act of production he was estranging himself from himself? (73)

Man is a species being, not only because in practice and in theory he adopts the species as his object (his own as well as those of other things), but--and this is only another way of expressing it--but also because he treats himself as the actual, living species; because he treats himself as a universal and therefore a free being. (75)

Appropriation appears as estrangement, as alienation; and alienation appears as appropriation, estrangement as true enfranchisement. (81)