Although each of the essays in this volume is a study complete in itself, they are connected by one and the same synthetic spirit, and are animated by one and the same object: that of demonstrating the utility in the biological, psychological, and sociological fields of the theorist, who, without having specialized in any particular branch or subdivision of science, may nevertheless bring into those spheres that synthetic and unifying vision which is brought by the theorist mathematician, with so much success, into the physico-chemical field of science.

This Book owes its origin to the indefinable sense of uneasiness and discontent into which I was thrown by the perusal of some of the best treatises on Logic. These treatises had failed to explain the nature of the logical or reasoning faculty, though purporting to indicate the laws which govern its proper functioning. Even the work of John Stuart Mill, which still remains in my opinion the best, was no more convincing than the rest. And the more I read of such books the less satisfied I became and the stonger became my desire to understand clearly what constituted reasoning. As for the...