Definitions of Intelligence

While intelligence tests of some sort appeared in human history as early as
the Old Testament book of Judges (7:3-7, 12:6), which indicates that early
Jewish society used questions and observations in personnel selection, the
intelligence test as it is known today can be traced to Renaissance Europe. In
1575, the Spanish physician Juan Huarte wrote Examen de Ingenios, a treatise
concerning individual differences in mental ability with suggestions for appropriate
tests. His work, and that of other investigators and theorists, was
the result of the rise of a middle class with aspirations to productive employment.
Previously, the aristocracy had controlled everything, and fitness for a
position was determined by lineage. Once this monarchical rule began to
break down, other means were necessary for determining who was fit for a
particular occupation and what might be the most productive use of a person’s
abilities. When it became apparent that royal blood was no guarantee
of competence, judgment, or mental acuity, the entire question of the origins
of intelligence began to occupy members of the scientific community.

For a time, the philosophy of empiricism led scientists toward the idea that
the mind itself was formed by mental association among sense impressions,
and sensorimotor tests were particularly prominent. As the results of these
tests failed to correlate with demonstrations of mental ability (such as marks
in school), however, other means were sought to measure and define intelligence.
The interest in intelligence testing in the nineteenth century was an
important aspect of the development of psychology as a separate scientific
discipline, and the twin paths of psychometric (that is, the quantitative assessment
of an individual’s attributes or traits) and statistical analysis on one
hand and philosophical conjecture concerning the shape and operation of
the mind on the other were joined in experimentation concerning methods
of assessing intelligence.
From their first applications in France as a diagnostic instrument, intelligence
tests have been used to help psychologists, educators, and other professionals
plan courses of action to aid individuals suffering from some mental
limitation or obstacle. This role has been expanded to cover the full
range of human intellectual ability and to isolate many individual aspects of
intelligence in myriad forms. The profusion of tests has both complicated
and deepened an understanding of how the mind functions, and the continuing
proposition of theories of intelligence through the twentieth century
resulted in an increasingly sophisticated battery of tests designed to assess
and register each new theory.