A test of conceptual thinking in which the subject classifies blocks according to different characteristicsdeveloped by the Soviet psychologist L. Vigotsky and introduced in the United States by J. Kasanin.This instrument was devised to study the process of thinking and concept formation, as contrasted with intelligence tests, which are primarily concerned with the products of thinking. On the Vigotsky the question is not so much whether the subject gets the correct answer to a problem, but how he arrived at his answer and how well he used his powers of abstraction. The information gained from the test is used not only in investigating the thinking process in general, but in detecting thought disturbances that do not appear in ordinary conversation.The test material consists of twenty- two blocks of different colors, shapes and sizes, each with a nonsense syllable printed on the under side. The subject is shown a block and its name (say, BIK), and asked to find all other blocks that belong with it. If the block marked BIK is red and triangular, he may select other red blocks or other triangular blocks. The examiner turns up these blocks and shows that they do not belong in the same category. The subject then continues to try different categories, and the examiner asks him to state each of his hypotheses aloud so that everything the subject says and does can be recorded. The correct categories require grouping according to combinations of characteristics that are not immediately apparent, such as flat-small, colored- tall, or green-flat-circular.The test is not usually scored quantitatively. The examiner studies the written record to determine the subject’s degree of flexibility (his willingness to give up incorrect hypotheses), resourcefulness (the number of alternative categories tried), and planfulness (the tendency to try different concepts in an organized way), as well as his general level of conceptualization. These observations are highly useful in diagnosis. It has been found that most people take a long time and make many errors before reaching the solution, but they can clearly state the reasons for each attempt. Moreover, when once they find the correct principle, they can apply it quickly and easily. Emotionally disturbed individuals on the other hand, show various peculiarities, such as sorting according to some obscure symbolism, or making patterns out of the blocks. Impairment in the ability to think abstractly is even more clearly indicated on this test. Schizophrenic patients and individuals with brain damage often point out the concrete differences of shape, color, and size but fail completely to see the more complex combinations. They are also unable to repeat a solution once it is found, and cannot adequately state the principle involved. If schizophrenics succeed in trying different solutions, they usually give bizarre reasons for their moves instead of clear hypotheses.