(Wechsler, 1944, p.4)
Intelligence is considered to be global as it characterises the individual's behaviour as a whole; it is a combination of those elements or abilities, which, though not entirely independent, are qualitatively differentiable. "By measurement of these abilities, we ultimately evaluate intelligence. But intelligence is not identical with the mere sum of these abilities, however inclusive". (Wechsler, 1944, p. 6) Wechsler suggests that there are three important reasons, which justify this statement:
(1) The ultimate products of intelligent behaviour are not only a function of the number of abilities or their quality but also of the way in which they are combined, that is, upon their configuration.
(3) Finally, while different orders of intelligent behaviour may require varying degrees of intellectual ability, an excess of any given ability may add relatively little to the effectiveness of the behaviour as a whole. It would seem that, so far as general intelligence is concerned, intellectual ability as such merely enters as a necessary minimum.
"Thus, to act intelligently, one must be able to recall numerous items i.e., have a retentive memory. But beyond a certain point and age in developmental life span, this ability does not help much in coping with life situations successfully". (Wechsler, 1944, p. ...
However the extent to which decline is confronted can be evaluated through various measurement tests and techniques. "Although intelligence is no mere sum of intellectual abilities, the only way we can evaluate it quantitatively is by the measurement of the various aspects of these abilities. There is no contradiction here unless we insist upon the identity of general intelligence and intellectual ability". (Wechsler, 1944, p. 8)
Researchers have always related intelligence to different mental processes. More recently psychologists have began to emphasize not only the processes but the content as well. They speak of memory but of auditory memory; not only of reasoning but of abstract, verbal or arithmetical reasoning. In a like manner some psychologists have begun to distinguish various kinds of intelligence. Thorndike, has suggested subdividing intelligence into three main types:
(1) Abstract or verbal intelligence, involving facility in the use of symbols;
(2) Practical intelligence, involving facility in manipulating objects;
(3) Social intelligence, involving facility in dealing with human beings.
The significant thing about this classification is that it emphasises upon the age criteria, accomplishments a person can achieve and how he can do it. This distinction between function and content is fully justified by experimental evidence. The rating, which an individual attains on an intelligence examination, depends to a considerable degree on the type of test used. His score on a test made up largely of verbal items may differ significantly from that obtained on a test involving questions of social comprehension and still more from another test made up of items involving predominantly psychomotor reactions and the perception of spatial relationships.