Marx on Alienation

Forgive the 19th century language:

What then constitutes the alienation of labour?

First, the fact that labour is external to the worker, i.e., it does not belong to his intrinsic nature; that in his work, therefore, he does not affirm himself but denies himself, does not feel content but unhappy, does not develop freely his physical and mental energy but mortifies his body and ruins his mind. The worker therefore only feels himself outside his work, and in his work feels outside himself. He feels at home when he is not working, and when he is working he does not feel at home. /his labour is therefore not voluntary, but coerced; it is forced labour. It is therefore not the satisfaction of a need; it is merely a means to satisfy needs external to it. Its alien character emerges clearly in the fact that as soon as no physical or other compulsion exists, labour is shunned like the plague. External labour, labour in which man alienates himself, is a labour of self-sacrifice, of mortification. Lastly, the external character of labour for the worker appears in the fact that it is not his own, but someone else's, that it does not belong to him, that in it he belongs, not to himself, but to another. Just as in religion the spontaneous activity of the human imagination, if the human brain and the human heart, operates on the individual independently of him - that is, operates as an alien, divine or diabolical activity - so is the worker's activity not his spontaneous activity. It belongs to another; it is the loss of his self.

As a result, therefore, man (the worker) only feels himself freely active in his animal functions - eating, drinking, procreating, or at most in his dwelling and in dressing-up, etc.; and in his human functions he no longer feels himself to be anything but an animal. What is animal becomes human and what is human becomes animal.

Karl Marx 1959 Economic and Philosophic Manuscripts of 1844. Lawrence & Wishart, pp.65-6.