Marx third lecture
A. In both "On the Jewish Question" and "Alienated Labor" Marx works with a vision of (we can say) human nature as a distinctive potential: to be a communal being, to live a life of free conscious productive activity. In both he complains that modern life is structured so as to prevent the actualization of this special potential. So modern life dehumanizes human beings.
B. He explains the alienation of labor under four heads (see his list: (1) and (2) on p. 137, (3) and (4) on p. 140).
1. From the object produced ("labor embodied and made material in a thing," p. 133). In modern industrial production, "the life which [the worker] has given to the object confronts him as something hostile and alien" (p. 134).
2. From one's own productive activity. One's work should be a self-affirmation, an expression of one's essential being. But in modern industrial production, one's productive activity becomes a commodity, which one sells. It becomes a mere means to subsistence — like merely animal production, "under the domination of direct physical need" (p. 139). Freedom retreats to the areas of life we share with mere animals (eating, drinking, sex); it isn't found in productive activity, though that ought to be the area of life where we affirm ourselves as human beings. "What is animal becomes human and what is human becomes animal" (p. 137).
3. From one's species-being. This is a way of making the same point. Human species-life is in principle free productive activity, but in modern industrial production work becomes a coerced means to merely physical existence (and existence as an individual, not as a communal being).
4. Alienation of one human being from another. Compare p. 104 on life in civil society as "bellum omnium contra omnes" (war of all against all, as in Hobbes' state of nature).
C. Marx's complaint isn't just that industrial workers (in 1844) live a physically deprived life (though he does make that complaint — see p. 135). See p. 144: "enforced increase of wages" wouldn't secure workers "their human significance and worth." Workers could be well paid and still be without human meaningfulness in their working lives.
D. Marx's prescription for what ails us: private property must be abolished (see p. 149). The "secret" of private property comes to light when its development reaches its "culminating point" (p. 143): namely, when the characteristic form of private property is not landholding, but capital (see p. 131). The "secret" of capital is that it's objectified labor from the past (a particular case of B.1 above), dominating present labor. But (Marx thinks) past labor should be a means to free human activity in the present, not something that enslaves human activity in the present. (See pp. 220-1.)