Extracts from Bertrand Russell, History of Western Philosophy (Chapter on Karl Marx):
The older materialism mistakenly regarded sensation as passive, and thus attributed activity primarily to the object.
For Marx, all sensation or perception is an interaction between subject and object; the bare object is a mere raw material, which is transformed in the process of becoming known.
Both subject and object are in continual process of mutual adaptation. Marx calls this process ‘dialectical’ because it is never fully adapted.