Raymond Cattell, along with John Horn, made significant contributions to our understanding of intelligence by distinguishing between two types: fluid intelligence and crystallized intelligence.

Fluid intelligence involves the capacity to solve new problems and adapt to unfamiliar situations. It's the type of intelligence individuals use when they encounter a novel problem or puzzle that requires innovative thinking. For instance, figuring out how to operate a new gadget relies heavily on fluid intelligence.

On the other hand, crystallized intelligence refers to the accumulation of knowledge and skills over time. This type of intelligence is what you draw upon when answering factual questions, like naming the capital of a country or recalling historical dates. Crystallized intelligence is built up through learning and experience and tends to increase as people age, while fluid intelligence is more susceptible to decline over time.

Cattell and Horn's work has been influential in the field of psychology, as it highlights that intelligence is not a single, unified construct but rather a combination of different cognitive abilities. Fluid and crystallized intelligence, while related, are distinct and serve different roles in how we process information and solve problems.