"The materialist theory of knowledge amounts, then, to this statement, that the human organ of cognition radiates no metaphysical light, but is a piece of Nature which pictures other pieces of Nature whose essence is explained when we describe it and bring it in connection with the whole Universe as the one Reality and the real Unity. Such a description demands from the epistemologist or philosopher that he should treat his subject in the same precise way as the animal world is treated by the zoologist. Should I be reproached with not following this precept immediately, I would point to Rome which, too, was not built in one day."

“Adherents of formal logic may be compared to a maker of porcelain dishes who would contend that he was simply paying attention to the form of his dishes, pots, and vases, but that he did not have anything to do with the raw material.”

“Much of what I have to say for my case may sound wonderful, because it runs counter to the popular prejudice, but the only witness required to prove the truth of my statements is the clear brain of my pupil, who has only to examine his own experience without preconceived notions, in order to find proofs on every hand.”

“Logic aims to instruct the human mind as to its own nature and processes; it will lay bare the interior working of our mind for our guidance. The object of the study of logic is thought, its nature, and its proper classification.”

“It is with logic as it is with other sciences. They draw wisdom from the mysterious source of plain experience. Agriculture, e. g., aims to teach the farmer how to cultivate the soil; but fields were tilled long before any agricultural college had begun its lectures. In the same way human beings think without ever having heard of logic. But by practice they improve their innate faculty of thought, they make progress, they gradually learn to make better use of it. Finally, just as the farmer arrives at the science of agriculture, so the thinker arrives at logic, acquires a clear consciousness of his faculty of thought and a professional dexterity in applying it.”

“It is a peculiarity of thought that it never stays with itself, but always digresses to other things.”

“My logic deserves its proletarian qualification for the reason that it requires for its understanding the overcoming of all prejudices by which the capitalist world is held together.”