ABSTRACT
The Weber-Fechner law correlates sensations with their physical causes; the theory of traces, and that of synaptic resistances, are speculations about the unknown physiological conditions or concomitants of sensation. The proper subject-matter of logic, thinking, is itself not a genus, but a name for certain activities having a peculiar connection with each other. Something of this sort may well be true of psychology. In some psychology the word ‘belief’ is used in the very same way as the word ‘judgment’ in logic. The methods characteristic of psychology are useless when one is thinking about thinking. It follows that the study of the nature of thinking can be no part of psychology if psychology necessarily involves measurement or experiment or introspection. Psychology is practically necessary to logic. The study of imagination and sensation is, like metaphysics and grammar, a non-logical study necessary to logic.
