Color
differences are always unsatisfactory in this comparison unless
transparency is also mentioned.) "Glass is square and wood is
round." "Glass is bigger than wood" (or _vice versa_). "Wood is
oblong and glass is square." "Glass is thin and wood is thick."
"Wood is made out of trees and glass out of windows." "There is
no glass in wood."

The two most frequent types of failures are misstatements
regarding color and thickness. The other failures are widely
scattered.

REMARKS. The test is one which all the critics agree in commending,
largely because it is so little influenced by ordinary school
experience. Its excellence lies mainly, however, in the fact that it
throws light upon the character of the child's higher thought processes,
for thinking means essentially the association of ideas on the basis of
differences or similarities. Nearly all thought processes, from the most
complex to the very simplest, involve to a greater or less degree one or
the other of these two types of association. They are involved in the
simple judgments made by children, in the appreciation of puns, in
mechanical inventions, in the creation of poetry, in the scientific
classification of natural phenomena, and in the origination of the
hypotheses of science or philosophy.

The ability to note differences precedes somewhat the ability to note
resemblances, though the contrary has sometimes been asserted by
logician-psychologists. The difficulty of the test is greatly increased
by the fact that the objects to be compared are not present to the
senses, which means that the free ideas must be called up for comparison
and contrast. Failure may result either from weakness in the power of
ideational representation of objects, or from the inadequacy of the
associations themselves, or from both. Probably both factors are usually
involved.

Intellectual development is especially evident in increased ability to
note _essential_ differences and likenesses, as contrasted with those
which are trivial, superficial, and accidental. To distinguish an egg
from a stone on the basis of one being organic, the other inorganic
matter requires far higher intelligence than to distinguish them on the
basis of shape, color, fragibility, etc. It is not till well toward the
adult stage that the ability to give very essential likenesses and
differences becomes prominent, and when we get a comparison of this type
from a child o