Ludwig Josef Johann Wittgenstein

“ In no branch of learning can an author disregard the results of honest research with so much impunity as he can in Philosophy and Logic. To this circumstance we owe the publication of such a book as Mr Coffey’s Science of Logic: and only as a typical example of the work of many logicians of to-day does this book deserve consideration. The author’s Logic is that of the scholastic philosophers, and he makes all their mistakes—of course with the usual references to Aristotle. ”

“ He confounds classes and complexes. (Mankind is a class whose elements are men; but a library is not a class whose elements are books, because books become parts of a library only by standing in certain spatial relations to one another—while classes are independent of the relations between their members.) [47] He confounds complexes and sums. (Two plus two is four, but four is not a complex of two and itself.) This list of mistakes could be extended a good deal.
The worst of such books is that they prejudice sensible people against the study of Logic. ”

“ He confounds the copula is with the word “is” expressing identity. (The word “is” has obviously different meanings in the propositions—
“Twice two is four”
and “Socrates is mortal.”)
[46] He confounds things with the classes to which they belong. (A man is obviously something quite different from mankind.) ”