" etc.
But every one knows what is meant by the term 8-year mentality, 4-year
mentality, etc., even if he is not able to define these grades of
intelligence in psychological terms; and by ascertaining experimentally
what intellectual tasks children of different ages can perform, we are,
of course, able to make our age standards as definite as we please.

Why should a device so simple have waited so long for a discoverer? We
do not know. It is of a class with many other unaccountable mysteries in
the development of scientific method. Apparently the idea of an
age-grade method, as this is called, did not come to Binet himself until
he had experimented with intelligence tests for some fifteen years. At
least his first provisional scale, published in 1905, was not made up
according to the age-grade plan. It consisted merely of 30 tests,
arranged roughly in order of difficulty. Although Binet nowhere gives
any account of the steps by which this crude and ungraded scale was
transformed into the relatively complete age-grade scale of 1908, we can
infer that the original and ingenious idea of utilizing age norms was
suggested by the data collected with the 1905 scale. However the
discovery was made, it ranks, perhaps, from the practical point of view,
as the most important in all the history of psychology.

2. _The kind of mental functions brought into play._ In the second
place, the Binet tests differ from most of the earlier attempts in that
they are designed to test the higher and more complex mental processes,
instead of the simpler and more elementary ones. Hence they set
problems for the reasoning powers and ingenuity, provoke judgments about
abstract matters, etc., instead of attempting to measure sensory
discrimination, mere retentiveness, rapidity of reaction, and the like.
Psychologists had generally considered the higher processes too complex
to be measured directly, and accordingly sought to get at them
indirectly by correlating supposed intelligence with simpler processes
which could readily be measured, such as reaction time, rapidity of
tapping, discrimination of tones and colors, etc. While they were
disputing over their contradictory findings in this line of exploration,
Binet went directly to the point and succeeded where they had failed.

It is now generally admitted by psychologists that higher intelligence
is little concerned in such elementary processes as those mentioned
above. Many of the animals have