History, Knowledge, and Essence in the Early Marx
D. Reidel Publishing Company
A careful study of the concept of essence which is found in Marx's early writings will show that his theory of knowledge does not involve, as is often claimed, the acceptance of an unknown thing-in-itself and does not imply that we can only know objects as they have been constituted for-us. We can know things as they are in-themselves. To show this will also require that we recognize and explain how the early Marx can hold that the object of knowledge is both constituted and that it reflects or copies things as they are in-themselves.
Kain, P. J. "History, Knowledge, and Essence in the Early Marx," Studies in Soviet Thought, 25 (1983): 261-83.