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From Stephen's Guide (16)
Fallacies of Definition
In order to make our words or concepts clear, we use a definition. The purpose of a definition is to state exactly what a word means. A good definition should enable a reader to 'pick out' instances of the word or concept with no outside help.
For example, suppose we wanted to define the word "apple". If the definition is successful, then the reader should be able go out into the world and select every apple which exists, and only apples. If the reader misses some apples, or includes some other items (such as pears), or can't tell whether something is an apple or not, then the definition fails.
The following are fallacies of definition:
1. Too Broad
Definition
The definition includes items which should not be included.
Examples
(i) An apple is something which is red and round.
(The planet Mars is red and round. So it is included in the definition. But obviously it is not an apple.)
(ii) A figure is square if and only if it has four sides of equal length.
(Not only squares have four sides of equal length; trapezoids do as well.
Proof
Identify the term being defined. Identify the conditions in the definition. Find an item which meets the condition but is obviously not an instance of the term.
2. Too Narrow
Definition
The definition does not include items which should be included.
Examples
(i) An apple is something which is red and round.
(Golden Delicious apples are apples, however, they are not red (they are yellow). Thus they are not included in the definition, however, they should be.)
(ii) A book is pornographic if and only if it contains pictures of naked people.
(The books written by the Marquis de Sade do not contain pictures. However, they are widely regarded as pornographic. Thus, the definition is too narrow.
(iii) Something is music if and only if it is played on a piano.
(A drum solo cannot be played on a piano, yet it is still considered music.)
Proof
Identify the term being defined. Identify the conditions in the definition. Find an item which is an instance of the term but does not meet the conditions.
3. Failure to Elucidate
Definition
The definition is harder to understand than the term being defined.
Examples
(i) Someone is lascivious if and only if he is wanton.
(The term being defined is "lascivious". But the meaning of the term "wanton" is just as obscure as the term "lascivious". So this definition fails to elucidate.)
(ii) An object is beautiful if and only if it is aesthetically successful.
(The term "aesthetically successful" is harder to understand than the term "beautiful".
Proof
Identify the term being defined. Identify the conditions in the definition. Show that the conditions are no more clearly defined than the term being defined.
4. Circular Definition
Definition
The definition includes the term being defined as a part of the definition.
(A circular definition is a special case of a Failure to Elucidate.)
Examples
(i) An animal is human if and only if it has human parents.
(The term being defined is "human". But in order to find a human, we would need to find human parents. To find human parents we would already need to know what a human is.)
(ii) A book is pornographic if and only if it contains pornography.
(We would need to know what pornography is in order to tell whether a book is pornographic.)
Proof
Identify the term being defined. Identify the conditions in the definition. Show that at least one term used in the conditions is the same as the term being defined.
5. Conflicting Conditions
Definition
The definition is self-contradictory.
Examples
(i) A society is free if and only if liberty is maximized and people are required to take responsibility for their actions.
(Definitions of this sort are fairly common, especially on the internet. However, if a person is required to do something, then that person's liberty is not maximized.)
(ii) People are eligible to apply for a learner's permit (to drive) if they have (a) no previous driving experience, (b) access to a vehicle, and (c) experience operating a motor vehicle.
(A person cannot have experience operating a motor vehicle if they have no previous driving experience.)
Proof
Identify the conditions in the definition. Show that they cannot all be true at the same time (in particular, assume that one of the conditions is true, then show from this that another of the conditions must be false |
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发表于 2003-6-26 17:16:00
