A systematic examination of how uniquely human mental faculties arose from non-conceptual antecedents, tracing psychological principles that enable conceptual thought. The author analyzes primitive ideas, the logic of recepts and concepts, and the roles of language, tone, gesture, articulation, and speech in mental development. He surveys philological evidence and considers transitions both in individual development and racial evolution, then outlines implications for intellect, emotion, volition, morality, and religion while aiming to establish general principles of mental evolution rather than detailed histories of each branch.