<P>All sciences need ways to classify the phenomena they investigate; chemistry has theperiodic table and biology a taxonomic system for classifying life forms. These classificationschemes depend on conceptual coherence, demonstrated correspondences across paradigms. Thisconceptual coherence has proved elusive in psychology, although recent advances have brought thefield to the point at which it is possible to define the type of classificatory system needed. Thisbook proposes a categorization of cognition based on core properties of constituent processes,recognizing correspondences between cognitive processes with similar underlying structure butdifferent surface properties. These correspondences are verified mathematically and shown not to bemerely coincidental.</P><P>The proposed formulation leads to general principles thattranscend domains and paradigms and facilitate the interpretation of empirical findings. It covershuman and nonhuman cognition and human cognition in all age ranges. Just as the periodic tableclassifies elements and not compounds, this system classifies relatively basic versions of cognitivetasks but allows for complexity. The book shows that a more integrated, coherent account ofcognition would have many benefits. It would reduce the conceptual fragmentation of psychology;offer defined criteria by which to categorize new empirical results; and lead to fruitful hypothesesfor the acquisition of higher cognition. </P>