The object and topic of the present work are sufficiently ex plained in the Introduction. The phrase Genetic Logic is there commented upon. I should prefer to use that phrase for the principal title; but remembering the varying meanings of the word Logic, I hesitate to do so, and adopt, at the publishers' suggestion, a title that is less severe, although, if taken literally, still sufficiently descriptive. It is Thought and its objects, Things, that the work treats of so Thought and Things is really my topic. The work is in line with certain endeavours characteristic of the time. The inroad of evolution and development theories.