Crystallized And Fluid Intelligence: Why You Need Both

Medically reviewed by April Justice, LICSW
Updated April 20, 2023by BetterHelp Editorial Team

The subject of human intelligence has been under investigation by cognitive psychology experts for well over a century. The first intelligence test used in America, "The Binet and Simon Tests of Intellectual Capacity," began its rise in popularity in 1908. Since that time, intelligence testing has evolved drastically, incorporating concepts such as fluid and crystallized intelligence. Research into new methods of intelligence testing has spurred numerous studies that attempt to understand precisely what makes a person intelligent and how to measure fluid intelligence and crystallized intelligence.

It is important to note that "intelligent" is not synonymous with "smart" or other positive descriptions of a person's aptitude. In years prior, researchers attempted to reduce a person's potential to a single score, the intelligence quotient (IQ). That effort has been mostly unsuccessful. Today's researchers and psychologists recognize the complexity of intelligence and cognition and generally break down a person's cognitive skills into three broad categories: crystallized intelligence refers to accumulated knowledge; fluid intelligence refers to problem-solving and adapting to new situations; and working memory.

Crystallized Intelligence

Crystallized intelligence refers to the accumulated knowledge a person can retain. When psychologists and researchers speak about crystallized intelligence, they are referring to a person's ability to apply previously acquired knowledge or prior learning to a problem in front of them. The phrase "long-term memory" is often associated with crystallized intelligence. Although crystallized intelligence and long-term memory are not synonymous, they are very similar concepts.

Crystallized intelligence is basically a person's "encyclopedia." It represents the bundled knowledge they have gained over the years, including everything from advanced concepts taught in school to basic knowledge like "birds have feathers." Because people continue to learn throughout their entire lives, crystallized intelligence increases the longer a person has been alive, resulting in higher crystallized intelligence.

When people solve a problem using crystallized intelligence, they look up facts and information in their personal encyclopedia. As an example, consider a doctor who specializes in a particular disease. After years of treating that disease, the doctor likely relies more on their own intuition than medical texts and resources. They have transferred the knowledge of that disease from medical literature to their personal encyclopedia, increasing their crystallized intelligence.

Fluid Intelligence

Fluid intelligence involves a person's ability to solve new and unfamiliar problems, which is distinct from crystallized intelligence. Imagine a person is asked to sort a bucket of marbles. The marbles are a variety of colors and shapes, and for the sake of this example, this person has never sorted marbles before. We could give this person instructions on how to sort the marbles, but that forces the person to rely on existing knowledge, a component of crystallized intelligence.

In our example, the person is given no additional information besides the direction to "sort the marbles." Deciding how the marbles should be categorized and the best method to sort them relies heavily on fluid intelligence. The person must examine the similarities and differences between the marbles and engage in problem-solving and critical thinking to figure out where they should be placed.

In reality, fluid intelligence and crystallized intelligence are always used together, often referred to as fluid vs crystallized intelligence. Even though we didn't give the person instructions on how to complete the task, crystallized intelligence was still involved. The person likely knew a little bit about how sorting works (put similar items together, etc.), and even knowing the definition of the word "sorting" relies on crystallized intelligence.

Unlike crystallized intelligence, which improves steadily over time, the fluid intelligence peak is typically in early adulthood, around age 20. Fluid reasoning slowly declines through adulthood, mainly due to changes in the brain due to aging.

A Note On Working Memory

crystallized intelligence

Need Motivation To Improve Your Intelligence?

Working memory isn't a category of intelligence in the same way as crystallized and fluid intelligence, but it is still an essential component of general intelligence. Working memory refers to a person's ability to hold on to information temporarily. Think of a person's working memory as their problem-solving workbench. The bigger the workbench, the more productively the person can work. A person with a high working memory can process more information than a person with a low working memory in the same span of time.

Working memory is closely related to fluid intelligence. In the past, researchers considered working memory a part of fluid intelligence. Today it is usually represented as its own category within the theory of fluid and crystallized intelligence types. The term "short-term memory" is often used interchangeably and illustrates the concept well. While crystallized intelligence (long-term memory) requires information to be retained indefinitely, short-term memory is like a scratchpad the brain can use to process information that does not need to be stored for later use.

Crystalized Vs. Fluid: Which Is Better?

Determining whether fluid intelligence is superior to crystallized intelligence, or whether the reverse is true, depends entirely on context. Some problems require more accumulated knowledge in a certain subject to solve (crystallized intelligence). In contrast, others rely heavily on in-the-moment critical thinking (fluid reasoning). While some problems certainly rely more on one type of intelligence than the other, in practice, both kinds of intelligence are required for every problem, making it essential to consider types of intelligence.

To an outside observer, it may appear that one type of intelligence is superior to the other. For example, those with more crystallized intelligence tend to do better academically, leading to an increase in confidence that propels the person to higher levels of achievement.

Fluid reasoning, while just as important, is less visible than crystallized intelligence. Consider a high school student with average fluid reasoning abilities who is enrolled in five classes: math, history, literature, science, and geography. Of those, just one subject relies heavily on fluid reasoning, math. The other subjects listed require much more rote memorization of facts and concepts. If the student has a strong ability to crystalize new knowledge, they will do better in all subjects. If the student has a lower ability to crystalize new knowledge, they will likely need help to perform well in school, regardless of their problem-solving ability.

Because academic achievement is linked so highly to intelligence, there exists a common misconception that a high ability to crystalize knowledge is what makes a person intellectually capable. However, there is a large gap between what society considers to be examples of intelligence and what researchers know to be true. Every person needs crystallized and fluid intelligence, and they both play a role in success, academic or otherwise.

crystallized intelligence

Can Crystallized And Fluid Intelligence Be Improved?

Almost anyone, through effort, can make themselves more intelligent. However, this process usually relies on improving crystallized intelligence. A person's crystallized intelligence improves every time they learn and retain something new. All a person needs to do to improve their crystallized intelligence continues to learn and grow. Often the main barrier to improving crystallized intelligence isn't a person's intellect but whether they feel confident enough to engage in the learning process.

Fluid intelligence is more complex. It relies on cognitive processes that decline as the brain ages, and improving fluid reasoning is more complex than improving crystallized intelligence. For many years, researchers assumed that fluid intelligence was fixed and that any attempt at improving it would be futile. However, recent research suggests the opposite. In a controlled study published in a psychological review, scientists were able to improve fluid intelligence scores after administering a course of specially designed training.

The training developed by the researchers didn't improve fluid reasoning directly. Instead, the training focused on enhancing the participant's working memory. Working memory, or a person's ability to hold on to information temporarily, is closely linked to fluid reasoning. In essence, a person can improve their fluid reasoning by processing larger amounts of information in the same amount of time. While it is not possible to make the same gains in working memory and fluid reasoning as in more crystallized intelligence, a significant degree of improvement is likely possible.

The working memory training investigated by scientists is still under development, and more research needs to be conducted before empirically-supported tools for improving fluid intelligence are widely available. For now, the best ways to improve intelligence overall rely on improving crystallized intelligence.

How Can Online Therapy Improve My Crystallized Intelligence?

Online therapy can help you find the confidence you need to achieve your crystallized intelligence goals, such as learning a new language or tackling complex tasks. Improving crystallized intelligence, as intelligence refers to the ability to retain and apply information, requires not only retention skills but also motivation and confidence. The process may appear challenging for someone who doesn't consider themselves a natural learner, but all people are able to improve their intelligence, regardless of their ability. Using empirically-supported techniques like Motivation Enhancement Therapy, a therapist can help you find the drive to improve your crystallized intelligence. Tools like Raven's Progressive Matrices, which are part of the progressive matrices family of assessments, can be utilized to measure crystallized intelligence progress over time.


Although it may seem like intelligence is innate and fixed, nothing could be further from the truth, especially in the context of autism spectrum disorders and developmental disorders. Crystallized intelligence can be continually improved throughout the lifespan. As evidenced by OECD education working papers, it's vital to develop confidence and a desire for learning when improving intelligence; the more time a person spends learning new things, the higher their crystallized intelligence becomes. There may be tools to strengthen fluid reasoning in the future, but for now, the best and most reliable way to increase intelligence is to become a life-long learner and consistently measure crystallized intelligence progress.

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