ldren 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

in which X is the internal and intrinsic part peculiar to the
individual life, it may be said that every individual has his X. But
in order to _approach_ to direct knowledge of X, it is essential to
know P and E.

He who carries out an examination, or supposes himself to be
performing a "psychical measurement" by dwelling on psychical results,
is in reality measuring a mixture of two unknown quantities, one of
which, being external to the individual, nullifies the results of
research.

Hence, to study individual differences in isolated activities, such as
the perception of colors, musical sounds, the letters of the alphabet;
or the capacity for observation of surroundings and the detection of
errors; or coordination of movements, language, etc., it is essential
to have first determined a _constant_ element: the means of
development offered by environment.

Here a simple and clearly defined difference between pedagogy and
psychology manifests itself: pedagogy determines experimentally the
means of development and the method of applying them while respecting
the internal or personal liberty of the individual; psychology studies
average reactions or individual reactions in the species or the
individual. But the two things are two aspects of a single fact, which
is the development of man; the individual and the environme