Most psychologists agreed that Spearman’s subdivision of abilities was too narrow, but not all agreed that the subdivision should be hierarchical. The American psychologist Joy Paul Guilford proposed a structure-of-intellect theory, which in its earlier versions postulated 120 abilities. In The Nature of Human Intelligence (1967), Guilford argued that abilities can be divided into five kinds of operation, four kinds of content, and six kinds of product. These facets can be variously combined to form 120 separate abilities. An example of such an ability would be cognition (operation) of semantic (content) relations (product), which would be involved in recognizing the relation between lawyer and client in the analogy problem above (lawyer is to client as doctor is to __). Guilford later increased the number of abilities proposed by his theory to 150.

Eventually it became apparent that there were serious problems with the basic approach to psychometric theory. A movement that had started by postulating one important ability had come, in one of its major manifestations, to recognize 150. Moreover, the psychometricians (as practitioners of factor analysis were called) lacked a scientific means of resolving their differences. Any method that could support so many theories seemed somewhat suspect. Most important, however, the psychometric theories failed to say anything substantive about the processes underlying intelligence. It is one thing to discuss “general ability” or “fluid ability” but quite another to describe just what is happening in people’s minds when they are exercising the ability in question. The solution to these problems, as proposed by cognitive psychologists, was to study directly the mental processes underlying intelligence and, perhaps, to relate them to the facets of intelligence posited by psychometricians.

In Guilford’s Structure of Intellect (SI) theory, intelligence is viewed as comprising operations, contents, and products. There are 6 kinds of operations (cognition, memory recording, memory retention, divergent production, convergent production, evaluation), 6 kinds of products (units, classes, relations, systems, transformations, and implications), and 5 kinds of contents (visual, auditory, symbolic, semantic, behavioral). Since each of these dimensions is independent, there are theoretically 180 different components of intelligence.

Guilford researched and developed a wide variety of psychometric tests to measure the specific abilities predicted by SI theory. These tests provide an operational definition of the many abilities proposed by the theory. Furthermore, factor analysis was used to determine which tests appeared to measure the same or different abilities.

Parenthetically, it is interesting to note that a major impetus for Guilford’s theory was his interest in creativity (Guilford, 1950). The divergent production operation identifies a number of different types of creative abilities.

IntelleQuest Education Company Three Dimensions of the SI Model |  IntelleQuest Education Company

The Contents Dimension

This dimension includes the broad areas of information in which operations are applied. It has been divided into four categories. • Visual - Information arising from stimulation on the retina in the form of an image.

       Auditory – Information arising from stimulation of the cochlea of the ear as image.

       Symbolic - Information perceived as symbols or signs that have no meaning by themselves; for example, Arabic numerals or the letters of an alphabet.

       Semantic - Information perceived in words or sentences, whether oral, written, or silently in one’s mind.

       Behavioural – Information perceived as acts of an individual/ individuals.

The Operations Dimension

This consists of five kinds of operation or general intellectual processes:

       Cognition - The ability to understand, comprehend, discover, and become aware. Cognition has to do with the ability to perceive the various items. For example, the cognition of semantic units has to do with one's ability to recognize words, i.e. one's vocabulary. Cognition of Behavioral Transformations would be the ability to perceive changes in the expressions of an individual.

       Memory - The ability to memorise information. Memory has to do with the ability to store and retrieve various kinds of information. People differ in their abilities to remember not only from other people, but also among various kinds of information. Some people who are poor at remembering faces (behavioral units) may be excellent at remembering puns (semantic transformations).

       Divergent Production - The process of generating multiple solutions to a problem. Divergent production has to do with the ability to access memory. It refers to the ability to find large numbers of things which fit certain simple criteria. For example, the ability to divergently produce visual units includes the ability to list a great many images which include a circle. Divergence in behavioral transformations would include the ability to revise stories about people. Divergence in Symbolic Implications would include the ability to list various equations which can be deduced from given equations.

       Convergent Production - The process of deducing a single solution to a problem. Convergent Production is the search of memory for the single answer to a question or situation. This area includes most areas of logic type problem solving. It differs from divergence in the constraint of one right answer. It seems likely that performance on convergent tasks is actually the result of divergent production and evaluation, but it is an often tested for skill, and the one most often associated with IQ.

       Evaluation - The process of judging whether an answer is accurate, consistent, or valid. Evaluation is the ability to make judgments about the various kinds of information, judgments such as which items are identical in some way, which items are better, and what qualities are shared by various items.

The Products Dimension

As the name suggests, this dimension contains results of applying particular operations to specific contents. There are six kinds of products, they are:

       Unit - Represents a single item of information.

       Class - A set of items that share some attributes.

       Relation - Represents a connection between items or variables; may be linked as opposites or in associations, sequences, or analogies.

       System - An organisation of items or networks with interacting parts.

       Transformation - Changes perspectives, conversions, or mutations to knowledge; such as reversing the order of letters in a word.

       Implication - Predictions, inferences, consequences, or anticipations of knowledge.

Some examples may provide a feel for the kinds of distinctions made in this model. Suppose a subject is given a long list of unrelated words to study and is asked to recall them later. The content of this scale is “semantic,” since it involves words; the operation is “memory”; and the product is the recall of words as “units.”

Therefore, according to Guilford there are 5 x 5 x 6 = 150 intellectual abilities or factors. Each ability stands for a particular operation in a particular content area and results in a specific product, such as Comprehension of Figural Units or Evaluation of Semantic Implications.

Guilford’s original model was composed of 120 components because he had not separated Figural Content into separate Auditory and Visual contents, nor had he separated Memory into Memory Recording and Memory Retention. When he separated Figural into Auditory and Visual contents, his model increased to 5 x 5 x 6 = 150 categories. When Guilford separated the Memory functions, his model finally increased to the final 180 factors [Guilford, J.P. (1988). Some changes in the structure of intellect model. Educational and Psychological Measurement, 48, 1-4.


SI theory is intended to be a general theory of human intelligence. Its major application (besides educational research) has been in personnel selection and placement. Meeker (1969) examines its application to education.


The following example illustrates three closely related abilities that differ in terms of operation, content, and product. Evaluation of semantic units (EMU) is measured by the ideational fluency test in which individuals are asked to make judgements about concepts. For example: “Which of the following objects best satisfies the criteria, hard and round: an iron, a button, a tennis ball or a lightbulb? On the other hand, divergent production of semantic units (DMU) would require the person to list all items they can think of that are round and hard in a given time period. Divergent production of symbolic units (DSU) involves a different content category than DMU, namely words (e.g., “List all words that end in ‘tion’). Divergent production of semantic relations (DMR) would involve the generation of ideas based upon relationships. An example test item for this ability would be providing the missing word for the sentence: “The fog is as ____ as sponge” (e.g., heavy, damp, full).


1.     Reasoning and problem-solving skills (convergent and divergent operations) can be subdivided into 30 distinct abilities (6 products x 5 contents).

2.     Memory operations can be subdivided into 30 different skills (6 products x 5 contents).

3.     Decision-making skills (evaluation operations) can be subdivided into 30 distinct abilities (6 products x 5 contents).

4.     Language-related skills (cognitive operations) can be subdivided into 30 distinct abilities (6 products x 5 contents).

Critical evaluation of Guilford's structure-of-intellect theory

The structure-of-intellect (SI) theory is evaluated within a framework of considerations of capitalization on chance. This empirical problem is placed in a larger perspective of concern for the general conceptual value of the theory in the study of human intelligence. The factor analytic support for the theory is found to be lacking in several notable respects. At best the research intended to support the model must be considered exploratory. But the model has provided a useful scheme for test construction and for indicating interesting hypotheses about qualities of intellect. Even in this context, however, there are several problems with the theory. The theory provides only a static taxonomy and thus affords very limited possibilities for understanding developmental issues.