An Introduction to Critical Thinking and Creativity - always yours

26 DEFINITIONS
sophisticated sense. Precising definitions allow us to refine questions, so we can
gain a better understanding of how to answer them.
3.4 CRITERIA FOR GOOD DEFINITIONS
We have said that a reportive definition should not be too wide or too narrow. Here
are more criteria for evaluating all kinds of definitions, not just reportive ones.
3.4.1 Use intensional definitions if possible
Philosophers very often draw a distinction between the extension and intension
of a term (or concept). The extension of a term is the set of things to which the
term applies. So for example, the extension of prime number is set of numbers
{2, 3, 5, 7, 11, 13,...}. On the other hand, the intension of a term is its meaning.
The intension of prime number would be "any integer larger than one which is
completely divisible only by one and itself."
When we define a term, should we define it by extension or intension? It depends,
but we should use intensional definition where possible. A term such as
human beinghas a very large extension. It is impossible to define the term by listing
all the human beings there are. Furthermore, even if we are able to list all the
items in the extension of a term, this might not explain the criterion for including
them. Defining prime numbers as 2, 3, 5, 7, 11, ... fails to explain how the numbers
are selected and how the list should continue. An intensional definition is
better. However, in some situations, an intensional definition might not be available.
The seven deadly sins, for example, is understood as referring to pride, greed,
envy, anger, lust, gluttony, and sloth. There is of course a long story about the history
of the term and why it is these seven sins that appear on the list. However,
this history is not relevant to the definition of the list.
3.4.2 Avoid circularity
A good definition should avoid circularity. A circular definition is one where the
definiens cannot be understood without knowing the meaning of the definiendum.
Consider the definition of time as "a quantity measured by clocks or watches."
This definition is circular because we cannot fully explain what clocks and watches
are without taking them as instruments that measure time. Similarly, sometimes
people say "the meaning of life is to search for the meaning of life." This sounds
profound, but taken as a definition, it is hopelessly circular and does not make
much sense. If the meaning of life is to search for the meaning of life, then it follows
that the meaning of life is to search for a search for the meaning of life, which
is to search for a search for a search of the meaning of life, and so on. Of course, on
a more charitable interpretation, perhaps the suggestion is that the mere process
of searching for the meaning of life is itself sufficient to make one's life meaningful.
But this does not seem very plausible. Imagine a selfish and bitter person who