Defining and Categorizing Intelligence

While psychologists have defined it many different ways over time, most current definitions of intelligence describe it as the ability to gather knowledge and skills and put them to use, including intellectual ability, possession of specific skills, and the ability to reason abstractly. Scores tend to correlate highly across different measures of intellectual ability. This led English psychologist Charles Spearman to suggest that a general intelligence factor, also known as g, underlies intellectual ability. General intelligence is the broad mental capacity that influences performance on all tasks measuring cognitive ability. Spearman also noted that more specific abilities also influence performance on intellectual tasks.

Early researchers thought sensory capacity, or the degree of sense organ sensitivity, would predict intelligence. Hearing and vision did not prove strong predictors of intelligence, but there are basic capacities that underlie intellectual ability. Processing speed is the rate at which someone takes in information, makes sense of it, and forms a response. People able to process a large amount of information quickly score higher on intelligence tests. People with especially slow processing speed often have academic and social difficulties. They find it difficult to keep up with a lecture or follow the flow of conversation in a group.

Processing speed is strongly related to fluid intelligence, the ability to find new ways to solve problems or perform tasks. Fluid intelligence is measured by performance on tests related to speed and abstract reasoning. Test takers may be asked to identify visual patterns or solve logic puzzles. Fluid intelligence rises through the young adult years before slowly declining with age. In contrast, crystallized intelligence involves knowledge accumulated over time. For example, a vocabulary test measures one aspect of crystallized intelligence. Crystallized intelligence does not depend on processing speed and can continue to increase throughout life. Both fluid and crystallized intelligence contribute to g. Also central to intelligence, abstract thinking involves the ability to think about concepts and principles, identify patterns, and make generalizations about classes of objects. It may involve considering objects that are not physically present or ideas that cannot be perceived by the senses (such as freedom). Psychologists measure abstract thinking in many ways. Some tests assess a person's ability to understand conceptual ideas, use spatial reasoning, or use metaphors and analogies (for example, understanding that a relationship described as "a ship at sea in a storm" is tumultuous and at risk of ending badly). Other tests evaluate the ability to employ critical thinking and reasoning (for example, to solve a clever riddle).

Intelligence predicts academic and occupational success, but other traits also play a key role. Social skills, curiosity, and grit (responding to challenges with determination and hard work) also contribute to success. Realizing its complexity, psychologists have developed many different models of intelligence. Some models include skills that go beyond academic knowledge and quick thinking, extending to musical, interpersonal, and physical skills.

In the early 1980s, American psychologist Howard Gardner suggested that traditional views of intelligence are far too limited. He proposed the idea that people have multiple forms of intelligence, expanding the definition of intelligence to capture a range of abilities and talents. Gardner's nine intelligences included musical, visual-spatial, verbal-linguistic, logical-mathematical, bodily-kinesthetic, interpersonal, intrapersonal, naturalistic, and existential intelligence. For example, professional athletes might have high bodily-kinesthetic intelligence, or a highly refined physical coordination, and a religious leader might have high existential intelligence, or a sophisticated sensitivity to deep questions about the purpose of life. Gardener states that everyone's abilities will vary across intelligences. A person may have weak verbal skills but excel at art, dance, and understanding others.

Many psychologists and educators have criticized Gardner's theory as overly broad. They suggest that some of his intelligences should be considered hobbies, talents, or personality traits. Despite these criticisms and limited research support, Gardner's theory of multiple intelligences is popular among educators. American psychologist Robert Sternberg shared Gardner's sense that intelligence was more complex than previously thought. In the early 1980s he proposed a triarchic, or three-pronged, theory of analytical, creative, and practical intelligence. The analytical component involves the ability to manage academic and analytical problem-solving using logic. It is strongly related to measures of general intelligence. The creative component allows a person to think of new ideas and adapt in any situation. It contributes to artistic abilities. The practical component assists a person in handling everyday tasks where numerous solutions are possible and multitasking is required. It involves academic knowledge and social skills.
Sternberg's triarchic theory of intelligence directly relates to convergent and divergent thinking. Convergent thinking is a cognitive process in which a person searches for a single, correct answer to a question or problem. This type of analytical thinking is supported by facts, knowledge, logic, and an academic environment. For example, convergent thinking would be used to narrow down the possible answers to a multiple-choice test question to the one correct answer. Divergent thinking is a cognitive process in which a person develops many unique, creative responses to a question or problem. For example, divergent thinking would be used to think of responses to an essay test question asking about possible ways to solve a social welfare problem. Creative and divergent thinking are supported by expertise and imagination. For example, creativity in designing a new engine is supported by a rich understanding of existing engine designs and of the materials available for creating engine parts. Intrinsic motivation (being driven by internal satisfaction) and a supportive environment also support divergent thinking. Practical thinking involves the ability to appropriately balance convergent and divergent thinking in everyday life.