EXCERPT This is a book which, despite its difficulty, has continued to gain ground. With the first edition long out of print, a second edition has become necessary. This second edition reproduces the text of the first, given its final form thanks to the faithful efforts of Georges Canguilhem and Charles Ehresmann. Contemporary logicians readily consign to ‘prehistory’ all writings on logic prior to the 1910 publication of Whitehead and Russell’s Principia Mathematica. And since that publication, the study of logic has developed at such a rate and in such diverse directions that it might be said, without yielding to scepticism, that any attempt at synthesis is doomed to ‘instant obsolescence’. We might even say that it has now become impossible to separate logic from contemporaneity. Yet the book Jean Cavaillès wrote in 1942, almost twenty years ago now, remains timely, in 1970, for both logicians and philosophers…