"At the present time it is of course quite customary for physicists to trespass on chemical ground, for mathematicians to do excellent work in physics, and for physicists to develop new mathematical procedures... Trespassing is one of the most successful techniques in science."

“respond to an objective constellation of millions of stimuli by developing, first of all, an organised field, many and perhaps the most essential properties of which have no physical partner among the single stimuli.”

“For the most part similarities of various degrees will occur in one perceptual situation; and then specific perceptual units will be formed not simply because their members resemble each other, but because their mutual resemblance is greater than is that of such members and any other parts of the situation.”

“At a given time some concrete forms are simply there in vision, not less than colors and brightnesses.”

“If we wish to imitate the physical sciences, we must not imitate them in their contemporary, most developed form; we must imitate them in their historical youth, when their state of development was comparable to our own at the present time. Otherwise we should behave like boys who try to copy the imposing manners of full-grown men without understanding their raison d’être, also without seeing that in development one cannot jump over intermediate and preliminary phases.”

“I do not deny that objective experience is imbued with acquired meaning in many respects... Probably no experience escapes from the influence of meaning.”

“Beyond some bars, out of arm's reach, lies an objective ; on this side, in the background of the experiment room, is placed a sawn-off castor-oil bush, whose branches can be easily broken off. It is impossible to squeeze the tree through the railings, on account of its awkward shape; besides, only one of the bigger apes could drag it as far as the bars. Sultan is let in, does not immediately see the objective, and, looking about him indifferently, sucks one of the branches of the tree. But, his attention having been drawn to the objective, he approaches the bars, glances outside, the next moment turns round, goes straight to the tree, seizes a thin slender branch, breaks it off with a sharp jerk, runs back to the bars, and attains the objective. From the turning round upon the tree up to the grasping of the fruit with the broken-off branch, is one single quick chain of action, without the least 'hiatus', and without the slightest movement that does not, objectively considered, fit into the solution described.”