15 quizzes, in five subjects
Knowing things, explained
TWO KINDS OF INTELLIGENCE · CATTELL, 1963
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Fluid: solving new problemsCrystallized: what you know
Illustrative trend. Fluid reasoning peaks early; knowledge keeps building, with vocabulary peaking in the late 60s in Hartshorne and Germine's 2015 data.“Dark matter”Adult knowledge is underratedMiddle-aged adults outscored younger ones on most knowledge domains, even where reasoning tests favour the young (Ackerman, 2000).
RetrieveSpaceRepeatQuizzing is how facts stickAnswering from memory, then checking, beats rereading for long-term recall. Every quiz is a free study session.
- Cattell, R. B. (1963). Theory of fluid and crystallized intelligence: A critical experiment. Journal of Educational Psychology, 54(1), 1–22.
- Hartshorne, J. K., & Germine, L. T. (2015). When does cognitive functioning peak? The asynchronous rise and fall of different cognitive abilities across the life span. Psychological Science, 26(4), 433–443.
- Ackerman, P. L. (2000). Domain-specific knowledge as the "dark matter" of adult intelligence. Journal of Gerontology: Psychological Sciences, 55B(2), P69–P84.