[...] Alienated labour had four aspects to it. First, the workers were related to the product of their labour as to an alien object; it stood over and above them, opposed to them with a power independent of the producers. Second, the workers became alienated from themselves in the very act of production; for workers did not view their work as part of their real life and did not feel at home in it. Third, peoples’ ‘species-life’, their social essence, was taken away from them in their work which did not represent the harmonious efforts of people as ‘species-beings’. Fourth, individuals found themselves alienated from other individuals. [...]
in the first part of the Economic and Philosophical Manuscripts