THE HEREDITARIAN THEORY OF IQapproaches of craniometry and the search for Lombroso's anatom-
ical stigmata, and decided instead on "psychological" methods. The
literature on mental testing, at the time, was relatively small and
decidedly inconclusive. Galton, without notable success, had exper-
imented with a series of measurements, mostly records of physiol-
ogy and reaction time, rather than tests of reasoning. Binet decided
to construct a set of tasks that might assess various aspects of rea-
soning more directly.
In 1904 Binet was commissioned by the minister of public
education to perform a study for a specific, practical purpose: to
develop techniques for identifying those children whose lack of
success in normal classrooms suggested the need for some form of
special education. Binet chose a purely pragmatic course. He
decided to bring together a large series of short tasks, related to
everyday problems of life (counting coins, or assessing which face
is "prettier," for example), but supposedly involving such basic
processes of reasoning as "direction (ordering), comprehension,
invention and censure (correction)" (Binet, 1909). Learned skills
like reading would not be treated explicitly. The tests were admin-
istered individually by trained examiners who led subjects through
the series of tasks, graded in their order of difficulty. Unlike pre-
vious tests designed to measure specific and independent "facul-
ties" of mind, Binet's scale was a hodgepodge of diverse activities.
He hoped that by mixing together enough tests of different abili-
ties he would be able to abstract a child's general potential with a
single score. Binet emphasized the empirical nature of his work
with a famous dictum (1911, p. 329): "One might almost say, 'It
matters very little what the tests are so long as they are
numerous.' "
Binet published three versions of the scale before his death in
- The original 1905 edition simply arranged the tasks in an
ascending order of difficulty. The 1908 version established the cri-
terion used in measuring the so-called IQ ever since. Binet decided
to assign an age level to each task, defined as the youngest age at
which a child of normal intelligence should be able to complete the
task successfully. A child began the Binet test with tasks for the
youngest age and proceeded in sequence until he could no longer
complete the tasks. The age associated with the last tasks he could
perform became his "mental age," and his general intellectual level