If we take a box twenty by fifteen by twelve inches, replace its cover and front side by bars an inch apart, and make in this front side a door arranged so as to fall open when a wooden button inside is turned from a vertical to a horizontal position, we shall have means to observe such [learning by trial and error]. A kitten, three to six months old, if put in this box when hungry, a bit of fish being left outside, reacts as follows: It tries to squeeze through between the bars, claws at the bars, and at loose things in and out of the box, stretches its paws out between the bars, and bites at its confining walls. Some one of all these promiscuous clawings, squeezings, and bitings turns round the wooden button, and the kitten gains freedom and food. By repeating the experience again and again the animal gradually comes to omit all the useless clawings, and the like, and to manifest only the particular impulse (_e.g._, to claw hard at the top of the button with the paw or to push against one side of it with the nose) which has resulted successfully. It turns the button around without delay whenever put in the box. It has formed an association between the situation _confined in a box with a certain appearance_ and the response of _clawing at a certain part of that box in a certain definite way_. Popularly speaking, it has learned to open a door by pressing a button. To the uninitiated observer the behavior of the six kittens that thus freed themselves from such a box would seem wonderful and quite unlike their ordinary accomplishments of finding their way to their food or beds.... A certain situation arouses, by virtue of accident or more often instinctive equipment, certain responses. One of these happens to be an act appropriate to secure freedom. It is stamped in in connection with that situation.[1] [Footnote 1: Thorndike: _Educational Psychology_, Briefer Course. p. 129.]