Fluid intelligence and crystal intelligence are two important concepts in psychology. Fluid intelligence refers to the flexibility and adaptability of individuals in dealing with new problems and unfamiliar tasks, while crystal intelligence refers to the ability of individuals to master the knowledge and skills accumulated in past study and experience.

1. Definition and characteristics of fluid intelligence

Fluid intelligence refers to the individual's intellectual ability in dealing with new problems and unfamiliar tasks, which involves unconventional and flexible thinking. Fluid intelligence does not depend on past learning and experience, but is mainly related to the individual's nervous system and cognitive ability. Fluid intelligence includes the ability to reason, solve problems and learn new tasks. It is more important in the early stage of cognitive development.

2. Definition and characteristics of crystal intelligence

Crystal intelligence refers to the intellectual ability of individuals to master the knowledge and skills accumulated in past study and experience, involving conventional and fixed thinking. Crystal intelligence depends on past study and experience, which is mainly related to personal cultural background and social experience. Crystal intelligence includes memory ability, vocabulary knowledge and subject skills in the learning process. It is more important in the later stage of cognitive development.

3. Testing of fluid intelligence and crystal intelligence

Fluid intelligence tests usually involve unconventional intelligence tasks such as reasoning, analogy and graphic reasoning, such as Raven intelligence test. Crystal intelligence test usually involves conventional intelligence tasks such as vocabulary, knowledge and subject skills, such as Wechsler intelligence scale.

4. Development of Fluid Intelligence and Crystal Intelligence

Fluid intelligence gradually declines with the increase of individual age, because it mainly depends on the development of nervous system and cognitive ability, and cognitive ability may weaken with age. Crystal intelligence is likely to grow with the growth of individual age, because it mainly depends on past study and experience, and with the growth of age, individuals will accumulate more knowledge and skills.

5. The connection between fluid intelligence and crystal intelligence.

Fluid intelligence and crystal intelligence interact in cognitive development. The development of fluid intelligence can help individuals learn and master knowledge better and improve the level of crystal intelligence. The accumulation of crystal intelligence can also affect the individual's ability to solve new problems and improve the level of fluid intelligence. In intelligence tests, fluid intelligence and crystal intelligence are often evaluated at the same time, because they both play an important role in the cognitive process.