If we were to compare two children, one of whom has had at his disposal the sixty-four colors in the conditions described above, and another who has been left to himself in poor surroundings, where gray and brown tints prevail, and who seems dull and unobservant, etc., we should find a very remarkable psychical difference. Such a difference is not, however, intrinsic; it might well be that, subjected to the same conditions as the first child, the second would recognize the sixty-four colors. The judgment we should give in such a case would be based upon an external factor, not upon internal potentialities. We should really be appraising two different environments, not two different individuals. To enable us to judge of individual differences, it would be necessary for the two children to have had _the same means of development_. In this case, if at the same age they were not equally capable of distinguishing the sixty-four colors, but if, for instance, one of the two could recognize only thirty of these, a true individual psychical difference would be apparent. One of the tests proposed by one of the greatest authorities on experimental psychology in Italy, to determine the intellectual level of sub-normal (backward or deficient) children, was to make a child pick out the largest and the smallest cube in a series. This choice, in common with nearly all the tests proposed for the same purpose, we considered quite independently of the influence of _culture_ and _education_; and it was appreciated as the expression of an intimate, personal activity of the intelligence itself. But if one of the deficient children I had educated on my method had been subjected to the test, he would, in virtue of a long sensory training, have chosen the largest and the smallest cube very much more easily than the children selected by the psychologist from his special schools; and my deficient child might even have been not only younger, but even more backward intellectually than the other. The test would therefore have measured the different methods of education, whereas the psychical differences between the two children, really existent by reason of age or of intellectual attainment, would have remained absolutely obscure. Man is a fusion of personality and education, and education includes the series of experiences he undergoes during his life. The two things cannot be separated in the individual: intelligence without acquirement is an abstraction. That which holds good of all living beings: that the individual cannot be divorced from his environment, is more profoundly true in its application to psychical life, because the content of environment, constituting the means of auto-experience which evolves man, is an essential part of him, and, indeed, is the individual himself. Nevertheless, we all know that the psychical individual is not his environment, but a life in himself. Given the formula P = X + E