He established that every test item measures a general factor (g) which is common to all items and a specific factor (s) which is unique to each item. Consequently, performance on an intelligence test is determined by two influences, where (g) is the more influential factor (Walsh & Betz 1995). .
To measure intelligence one should use mental tests that are saturated in (g) because individual differences in (g) translate into differing abilities in cognitive functioning. Emphasis on the content of test items were not consigned by Spearman. Essential elements of measuring intelligence are the education of relations and correlates. Education, which means bringing out, is the ability to react and to discover relationships; education of relations, or inductive reasoning, is inferring the general rule based on specific instances; and education of correlated, or deductive reasoning, which is recognising a specific instance or example of general rule. So the actual content of the test-item does not matter, it only provides a vehicle for assessment, as long as it assess our ability to think, reason and see relationships. The existence of (g) is still widely accepted, but some prefer to think of factors of mental ability somewhere between the global (g) and specific (s). These factors of intermediate generality, also called group factors, are the basis of the multiple factor theories of intelligence (Walsh & Betz 1995). .
2.3 Multiple Factor Theories.
These theories are founded on the results of factor analysis that established that while some common or shared variance could be attributed to tests' overlap with (g), there was another shared variance that seemed to reflect other common factors in mental tests. To illustrate, tests of verbal analogies and vocabulary have much in common, but this is not all (g), instead it is a group factor of verbal ability. Thurstone originated seven group factors that occurred consistently (Walsh & Betz, 1995).