Now, it must be obvious that for the measurement of anything so complex and multi-dimensioned as the human mind, no single test or scale can be established. One cannot measure the power of visual perception, for example, by the same scale that is used to measure attentiveness or initiative. As a matter of fact, psychologists no longer attempt to classify human abilities as narrowly as was once the popular practice. It is almost impossible for even an expert psychologist to be sure he knows just what qualities and all the qualities any particular test measures. This is because modern psychologists no longer group reactions into general functions such as memory, attention, reason, etc., but simply describe accurately the stimulus given and the conditions under which it was given and then describe just as accurately what the reaction is. The test may be built up, for example, to measure ability to recognize and classify words, but it will also depend upon ability to read the directions, ability to attend closely to horizontal and vertical lines and upon many other correlated abilities. Any test may measure primarily a particular mental dimension or ability but it is quite certain that the resulting score will be influenced by numberless other factors than the one that the examiner is most interested in measuring. But since one of the very best tests of intelligence is, of course, the degree to which one is able to profit by social contacts and the breadth and variety of the individual’s stored-up impressions, these extraneous or collateral qualities, which every test also more or less successfully measures in addition to the particular quality or mental dimension under direct examination, furnish useful data in arriving at a conclusion which is, after all, the main purpose sought, as to the individual’s actual abilities and potential powers. In order, however, to get at a really useful record of the mental capacity of an individual, we must apply a variety of tests and out of the sum total of the results of these tests we are able much more accurately to gauge the degree of possession of the qualities for which we are seeking than could possibly be done by any single test, no matter how skilfully constructed. Here again science confronts the popular human demand for a panacea. But just as in medicine only the quack offers a cure-all, so, in other fields, science has no single standard to offer by which all results in a given field may be accomplished, and psychology cannot now or at any time in the future pretend that by a single method or a single measurement mental capacity can be gauged.