Full Idea
As individuals express their life, so they are; what they are, therefore, coincides with their production, both with what they produce and with how they produce.
Gist of Idea
The nature of an individual coincides with what they produce and how they produce it
Source
K Marx / F Engels (The German Ideology [1846], §1.A)
Book Reference
Marx,K./Engels,F.: 'The German Ideology', ed/tr. Arthur,C.J. [Lawrence and Wishart 1985], p.42
A Reaction
This appears to be contradicted by their subsequent idea that 'alienation' from the means of production is possible. Presumably intellectuals (in all ages) are to some extent exempt from this rule. It is, in fact, not true.