Edward Bradford Titchener, « Functional Psychology and the Psychology of Act, II », Ithaca (New York), The American Journal of Psychology,  vol. 33, 1922, p. 79.

Stumpf’s act, lastly, lies between these other two. It is active, in the sense that it is found or given as active; it is by no means the deed of an I. It is an active verb, moving amidst phenomena and relations, and generating its « correlate » – a sort of caddis-worm that houses itself variously in the sticks and shells and stones of its independently variable surrounding.