According to American psychologist L. L. Thurstone (1938), intelligence comprises of nine distinct primary mental abilities. According to him, there is no factor common to all intellectual activity. However there afre a number of groups of mental abilities, each having its own primary factor.
The description of the factors is as follows : Verbal factor : It is concerned with comprehension of verbal relations, words and ideas.
Spatial factor : It is involved in any task in which the subject manipulates an object imaginatively in space.
Numerical factor : It is concerned with the ability to do numerical calculations rapidly and accurately.
Memory factor : It involves the ability to memorize quickly.
Word-fluency factor: It is involved whenever the subject is asked to think of isolated words at a rapid rate.
Inductive reasoning factor : It is the ability to draw inferences or conclusions on the basis of specific inferences.
Deductive reasoning factor : It is the ability to make use of generalized results. Perceptual factor : It is the ability to perceive objects accurately.
Problem solving factor : It is the ability to solve problems with independent efforts.
There stone assembled a battery of tests to measure these abilities. This Primary Mental Abilities test (PMA) is still widely used. The weakest part of the group factor theory was that it discarded the concept of common factor.
The weakest part of the group factor theory was that it discarded the concept of common factor.