Some of the differentiating principles in accordance with which the new stimuli will or will not call out the old response were observed. Two groups of human subjects reacted to stimulus figures, which consisted of two lines joined at their ends, drawn in black ink on cards, and which differed in size and degree of the angle. There is transfer on the basis of size of the angle when the S has been trained to make a size discrimination, and on the basis of direction of angle when S has been trained to discriminate direction of angle. There are varying degrees of ambiguity of transfer. The general similarity of the figure on the card in the test series to the figures used in the training series was found to be an adequate explanation of the results. The test stimuli used cannot be divided into two classes, equivalent and non-equivalent; the data must be treated in terms of resemblance. (PsycINFO Database Record (c) 2006 APA, all rights reserved)