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What Is a Category Mistake?

By J.E. Holloway
Updated May 23, 2024
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In philosophy, a category mistake, also called a category error, is a philosophical concept used to describe a statement in which the speaker presents a concept from one category as if it belongs in another, or ascribes properties from one category to concepts from another. British philosopher Gilbert Ryle (1900-1976) coined the term in his book "The Concept of Mind" (1949). The term caught on and is now widely used in philosophical discussion.

The most famous example of a category mistake is probably an example from Ryle's work. Ryle asks the reader to imagine a visitor to the city of Oxford. A guide shows the visitor all around the city, pointing out the colleges, department buildings and libraries as they go. At the end of the tour, the visitor asks "but where is the university?" For Ryle, this is a category mistake. The visitor is treating the university as if it were part of the category of buildings, rather than as what it actually is: a collection of institutions, some of which are housed in buildings of their own.

This example formed part of Ryle's criticism of the philosophy of Rene Descartes (1596-1650). To Ryle, Descartes was making a category mistake similar to that of the visitor who looked for the university while ignoring its components. Ryle argued that the mind was not separate from the body or the actions of the individual.

Some participants in philosophical discussions occasionally misapply the term incorrectly using it to mean any major error. To truly be a category mistake, a statement must attribute to something qualities that it could not possibly possess. Consider the statement "most Americans are vegetarian." This statement is not true, but it is not a category error, because theoretically it could be true: vegetarianism is a quality appropriate to the category of Americans. The statement "most Americans are about three quarters of an hour long" is this type of mistake, since it applies a quality — a duration of time — which does not apply to humans generally.

Obvious category mistakes such as this example are extremely rare, because they seem obviously false to the listener. Not all category errors are so obvious, however. In speech, a mixed metaphor, also known as catachresis, is essentially a form of category error which may be either unintentional or deliberate. In Shakespeare's Timon of Athens, for example, Philotus says "I fear 'tis deepest winter in Lord Timon's purse." In essence, this is a category mistake — purses do not have seasons — but the implied comparison is meaningful, providing a poetic comparison that illuminates and pleases at the same time.

What Is a Category Mistake in Philosophy?

In the context of philosophy, a category mistake occurs when qualities are attributed to things that they cannot possibly possess. Put another way, it’s when one category of things is inappropriately applied to another category. The term was originally coined by Gilbert Ryle, a British philosopher.

Ryle believed that separating categories was the central point of philosophy. Bertrand Russell was one of Ryle’s key influences, particularly in the nature of paradoxes. Since Ryle coined the term, there has been an ongoing discussion in the philosophical community as to what use category mistakes have when attempting to solve persistent philosophical questions.

One can test to see if something is a category mistake by attempting to combine or separate the first thing’s category from the second thing’s category without it sounding absurd. “Being outdoors boosts my mood” is not a category mistake, as the outdoors can be described as something that boosts one’s mood; each part of the statement can be combined without sounding insensible. “Being outdoors is the circumference of a circle” is a category mistake, as the outdoors cannot describe the circumference of a circle and is thus an absurd statement.

Category mistakes are of great interest to philosophers because they are ways in which we describe reality. Take the category mistake, “The number six is blue.” This would be considered a category mistake because the number six and the color blue are inherently separate and absurd when placed together in most contexts. However, does the fact that the statement seems absurd make it inherently insensible? Perhaps, if we viewed these two things in a different way, we could logically ascribe the color blue to the number six. This would require that we reshape our thinking of what the number six is and what the color blue is. Thus, the application of category mistakes may have profound implications on philosophy.

While Ryle officially coined the term “category mistake,” similar discussions have been held since as far back as Aristotle, who posed a puzzle regarding the quality of “snub.” According to the problem posed by Aristotle, the term “snub” can be used in the context of “snub nose” which could be considered a synonym for “concave nose.” This would indicate that the words snub and concave are synonymous. However, when the word “snub” is used to describe other things, such as “snub bowl,” it seems to be insensible, while “concave bowl” makes sense. When joined together, the terms “snub” and “bowl” appear to be a category mistake.

What Are Examples of a Category Mistake?

Ryle presented an easy-to-understand example of a category mistake in his 1949 work, “The Concept of Mind.” He presents a scenario in which a person is touring the city of Oxford. They are shown buildings such as libraries, department buildings, and colleges. The person asks, “But where is the university?” According to Ryle, this is a category mistake. The university, as something distinct from individual buildings, cannot be described as an individual building, as it is made up of a collection of institutions.

Ryle used this term as part of a criticism of Rene Descartes’ work. Descartes, in his own work, described the mind as a separate item from the body or actions of an individual. According to Ryle, Descartes was making a category mistake, as the mind cannot be considered separate from the body or actions of an individual. This presumably applies to all dualists who believe the mind and body are separate; or, more specifically, belong to separate categories.

The term category mistake is often misused in philosophical discussions to describe any large error. For example, the statement, “Most scientists have birthdays on September 29th” might be incorrectly described as a category mistake. For a category mistake to occur, something must be ascribed qualities that they inherently cannot have. Just because the statement is not true does not mean a category mistake has been made because it is a statement that could theoretically be true. Instead, the statement, “Most scientists are fewer than 100 pages long” would probably be described as a category mistake as the statement is inherently insensible; “100 pages long” can never be used to describe scientists.

These are obvious examples of category mistakes and many are less apparent. A mixed metaphor in itself could be described as a category mistake. “This photo of my children is the brightest sunshine” could be called a category mistake because a photo cannot actually be rays of light.

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