Defining is one of the most useful skills in critical thinking. When making and defending some claim, one should make the claim and the defense clearer by defining key terms. When attacking someone else's claims, beginning by questioning the definitions of key terms is generally easiest. The proper defining of key terms can prevent considerable waste of time and effort on mere verbal disputes. Verbal disputes occur when persons believe they disagree about some matter of substance, but in reality are just disagreeing in the way they use some key term or terms, and once they settle on single definitions for the terms in question they don't disagree at all.

For example, two people may argue about whether UFO's exist. If the person arguing that UFO's do exist merely means by 'UFO' flying objects which have never been identified, while the one disagreeing means by 'UFO' alien spacecraft visiting Earth, then it is quite possible for them to agree that no alien spacecraft visiting the Earth exist. But by neglecting to define their terms first, they may argue for a long time before they discover that they agree.

When questioning another's definitions and when attempting to provide useful definitions of one's own one must know what makes for good definitions and bad definitions. The act of pointing is ambiguous, so defining by pointing (an ostensive definition) is not really a good way to define something. Dictionary definitions often consist in the giving of a synonym; this could only provide a useful definition if the synonym has just one possible meaning and both parties know that meaning. Dictionaries do provide a useful starting point, but the best definitions for the purposes of critical thinking are those which give genus and differentia. The term being defined will represent some concept. The genus states to which more general kind of thing this concept belongs and the differentia states how this concept differs from others (other species) of that same general kind.

Six Rules For Definitions

  1. Include the genus and differentia.
  2. It must be neither too broad nor too narrow.
  3. It must state essential attributes (rather than trivial ones).
  4. It must not be circular.
  5. It must not be negative unless absolutely necessary.
  6. It should avoid vagueness, obscurity and metaphor.

 Warning: Web Page Notes are not intended as a substitute for attending lectures.