Human intelligence can be viewed as the ability to solve tasks, naturally given or artificially constructed. Intelligence differs from an instinct by its greater universality, as it can solve problems that have no direct biological significance. Intelligence also differs from the intuition as synthetic realisation of solution, without decomposing a problem. Intelligence is considered as an abstract capability inherent and common to all mental processes, i.e. feelings, memory, perception, imagination, and reasoning. Binet (2009) defined it as: ‘It seems to us that in intelligence there is a fundamental faculty, the alteration or the lack of which, is of the utmost importance for practical life. This faculty is judgment, otherwise called good sense, practical sense, initiative, the faculty of adapting ones self to circumstances’. For Anastasi (1992) intelligence is: ‘…not a single, unitary ability, but rather a composite of several functions. The term denotes that combination of abilities required for survival and advancement within a particular culture’. According to Piaget (1963):’ Intelligence is assimilation to the extent that it incorporates all the given data of experience within its framework . . .There can be no doubt either, that mental life is also accommodation to the environment. Assimilation can never be pure because by incorporating new elements into its earlier schemata the intelligence constantly modifies the latter in order to adjust them to new elements’.
Herbert Spencer (1851) radical English philosopher of the 19th Century is one of the first that linked intelligence to biology. He argued that intelligence is innate, inherited property. Interest in the evolution (published his own ideas before Darwin) led him to emphasize behavioral aspects of the intelligence, i.e. those that are associated with the behavior. For Spencer intelligence is the ability by which intelligent animals (including humans) adapt their behavior in a complex and constantly changing conditions in their environment.
There are many different theoretical approaches to intelligence.
Spearman (1904) believed that intelligence is a single, general ability, which manifests in all tests. Spearman's two-factor model of intelligence provides a more in-depth analysis - he assumed that the general ability or G factor requires some specific skills or factor. Spearman emphasised: ‘…G tends to dominate according as the performance involves the perceiving of relations, or as it requires that relations seen in one situation should be transferred to another. On weighing the evidence, many of us used to say that this G appears to measure some form of mental energy. But in the first place, such a suggestion is apt to invite needless controversy. This can be avoided by saying more cautiously that G behaves as if it measured energy. In the second place, however, there seems to be good reason for changing the concept of energy to that of "power" (which, of course, is energy or work divided by time). In this way, one can talk about mind power in much the same manner as about horsepower. G is in the normal course of events determined innately; a person can no more be trained to have it in higher degree than he can be trained to be taller’.
Catell (1963) underlines two broad types of the intelligence - fluid and crystallised intelligence. Fluid intelligence is influenced by the heritage and culturally unbiased. Fluid intelligence is giving its maximum around 14 years. Later results in intelligence tests begin slowly and rapidly to decline. Crystallised intelligence evolves under the influence of experience and culture. Maximum is achieved later in life but results in intelligence tests can grow until the end of life.
Guilford’s (1967) theory summarises: ‘ The structure of the intelligence is complex’. There are mental operations i.e. thinking processes, facilities ie. what we think and products i.e. results/scores of thinking. Each factor has its location in