i8o THE MIS MEASURE OF MAN
was calculated by subtracting this mental age from his true chron-
ological age. Children whose mental ages were sufficiently behind
their chronological ages could then be identified for special edu-
cational programs, thus fulfilling Binet's charge from the ministry.
In 1912 the German psychologist W. Stern argued that mental age
should be divided by chronological age, not subtracted from it,*
and the intelligence quotient, or IQ, was born.
IQ testing has had momentous consequences in our century. In
this light, we should investigate Binet's motives, if only to appreci-
ate how the tragedies of misuse might have been avoided if its
founder had lived and his concerns been heeded.
In contrast with Binet's general intellectual approach, the most
curious aspect of his scale is its practical, empirical focus. Many
scientists work this way by deep conviction or explicit inclination.
They believe that theoretical speculation is vain and that true sci-
ence progresses by induction from simple experiments pursued to
gather basic facts, not to test elaborate theories. But Binet was pri-
marily a theoretician. He asked big questions and participated with
enthusiasm in the major philosophical debates of his profession.
He had a long-standing interest in theories of intelligence. He pub-
lished his first book on the "Psychology of Reasoning" in 1886, and
followed in 1903 with his famous "Experimental Study of Intelli-
gence," in which he abjured previous commitments and developed
a new structure for analyzing human thinking. Yet Binet explicitly
declined to award any theoretical interpretation to his scale of
intelligence, the most extensive and important work he had done
in his favorite subject. Why should a great theoretician have acted
in such a curious and apparently contradictory way?
Binet did seek "to separate natural intelligence and instruction"
(1905, p. 42) in his scale: "It is the intelligence alone that we seek
to measure, by disregarding in so far as possible, the degree of
instruction which the child possesses.... We give him nothing to
read, nothing to write, and submit him to no test in which he might
* Division is more appropriate because it is the relative, not the absolute, magnitude
of disparity between mental and chronological age that matters. A two-year dispar-
ity between mental age two and chronological age four may denote a far severer
degree of deficiency than a two-year disparity between mental age fourteen and
chronological age sixteen. Binet's method of subtraction would give the same result
in both cases, while Stern's IQ measures 50 for the first case and 88 for the second.
(Stern multiplied the actual quotient by 100 to eliminate the decimal point.)