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Fallacies of definition refer to the various ways in which definitions can fail to have merit. The term is used to suggest analogy with the logical fallacies. This is a typical sort of list found in texts used in college logic courses.


If one concept is defined by another, and the other is defined by the first, we have a pair of circular definitions, somewhat similar to a question-begging argument: neither offers us enlightenment about the thing we wanted to be enlightened about.

Defining with a synonym

A definition is no good if it simply gives a one-word synonym. For example, suppose we define the word "virtue"—an important word in ethics—just using the word "excellence." It might be perfectly true that all virtues are excellences and all excellences are virtues, but the word "excellence" by itself is not a good definition of "virtue" in philosophy. One can always simply ask, "But what does 'excellence' mean?" Surely, if one has a basic confusion about what "virtue" means, then one will also have a basic philosophical confusion about what "excellence" means. So it will not do to define one simply by stating the other.

Defining with a near synonym

A definition does no good if it uses a very near synonym in the definition. For example, suppose we define 'beautiful' as 'possessing aesthetic value'. The words 'beautiful' and 'aesthetic' are very nearly the same in meaning; so if anyone is deeply confused or curious about beauty, then he is of course going to be confused or curious about the aesthetic. The question is what general characteristics are possessed by all beautiful objects, or all objects that have aesthetic value.

Over-broad definitions

Definitions can be too broad. Suppose we define 'bachelor' as 'unmarried male'. At first glance this might look correct, but male is a word that can apply to many things. For example, male dogs and male babies are not considered bachelors. A definition is too broad if it applies to things that are not part of the extension of the word defined. To correct this fallacy, narrow the definition. In this case, 'bachelor' can mean 'unmarried man'. However, the Pope, or a gay man in a long-term committed relationship, are not considered bachelors either - so it must further be narrowed to a man who is socially expected to have been able to marry, but has not yet.

Over-narrow definitions

Definitions can be too narrow. That is, they can exclude some things that they should apply to; they fail to describe some members of the word's extension. Here is an example of a narrow definition: 'piece of furniture' means 'object used to sit on'. Of course, some pieces of furniture are not used to sit on; for example, we put objects on them (like tables) or we put our feet on them (like footstools), and so forth. So even though some pieces of furniture are objects that are used to sit on, not all furniture is used to sit on. We need a broader definition: we might add other qualifying characteristics, like 'used to put feet up on' or 'used to put household objects on', for example. That would make the extension of the definition bigger--that is, the definition would apply to more things, and more of the things that we use the word 'furniture' to describe. We might also choose to entirely rewrite the definition, since laundry lists of characteristics strung together by 'or' are generally regarded by philosophers as not describing a unitary concept.


Definitions can go wrong by using ambiguous, obscure, or figurative language. Suppose we defined 'love' as 'the insensible quivering of the soul'. This is useless. Given a definition like this, one has the right to ask: but what is the insensible quivering of the soul? How would we recognize it? Is Johnny's soul insensibly quivering right now? And so on. Definitions should be stated in plain, straightforward language that can be understood by the people to whom the definitions are given. See jargon.

An often quoted example is Samuel Johnson's definition for oats: "Oats: a grain which in England is generally given to horses, but in Scotland, supports the people."

To which his Scots associate, James Boswell, replied "that is why England is chiefly noted for its beautiful horses, but Scotland for its beautiful women" (slight paraphrase).

Examples & Definition in Context

Examples are by themselves insufficient to define a term. For instance: "Chutzpah is killing your parents and then throwing yourself on the mercy of the court because you are an orphan." Such a definition is only useful if the reader has some larger context for the term being defined.

Even a series of examples may be inadequate. For example, "Edentates are mammals such as voles and tenrecs," does not help the reader to decide if, say, shrews are edentates or not.

Finally, striking examples can often combine with other definitional fallacies to create complex definitions that are still difficult for the unfamiliar reader to use. Thus, "Situationism is the intellectual framework of situationist movements such as the student protests in France in 1968." If we remove the example, the remaining definition is circular. So even this rather full-bodied definition does no good to a reader who wants to know if, say, Ann Coulter is a situationist.

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