of intelligence lies in comprehending together in a unitary,
meaningful whole, impressions and associations which are more or less
independent, heterogeneous, or even partly contradictory. "Intellectual
ability consists in the elaboration of a whole into its worth and
meaning by means of many-sided combination, correction, and completion
of numerous kindred associations.... It is a _combination activity_."

Meumann offers a twofold definition. From the psychological point of
view, intelligence is the power of independent and creative elaboration
of new products out of the material given by memory and the senses. From
the practical point of view, it involves the ability to avoid errors, to
surmount difficulties, and to adjust to environment.

Stern defines intelligence as "the general capacity of an individual
consciously to adjust his thinking to new requirements: it is general
adaptability to new problems and conditions of life."

Spearman, Hart, and others of the English school define intelligence as
a "common central factor" which participates in all sorts of
special mental activities. This factor is explained in terms of a
psycho-physiological hypothesis of "cortex energy," "cerebral
plasticity," etc.

The above definitions are only to a slight extent contradictory or
inharmonious. They differ mainly in point of view or in the location of
the emphasis. Each expresses a part of the truth, and none all of it. It
will be evident that the conception of Binet is broad enough to include
the most important elements in each of the other definitions quoted.

GUIDING PRINCIPLES IN CHOICE AND ARRANGEMENT OF TESTS. In choosing his
tests Binet was guided by the conception of intelligence which we have
set forth above. Tests were devised which would presumably bring
into play the various mental processes thought to be concerned in
intelligence, and then these tests were tried out on normal children of
different ages. If the percentage of passes for a given test increased
but little or not at all in going from younger to older children this
test was discarded. On the other hand, if the proportion of passes
increased rapidly with age, and if children of a given age, who on other
grounds were known to be bright, passed more frequently than children of
the same age who were known to be dull, then the test was judged a
satisfactory test of intelligence. As we have shown elsewhere,[13]
practically all of Binet's tests fulfill thes