the Body of Him'.  The definition 'The church is the Body' is in nowise

impaired if reversed 'The Body is the church'.

If the definition is a good one the subject and the predicate must be

reversible without prejudice to the sense.  Several rules have been laid down

for the framing of a definition:

'(1) The definition must be adequate; i.e., neither too extensive nor

too narrow for the thing defined; e.g. to define a "fish" as "an animal

that lives in water", would be too extensive, because many insects,

etc.  live in water.  To define a fish as "an animal that has an air -

bladder", would be too narrow, because many fish are without any'.

'(2) The definition must be in itself plainer than the thing defined.

This rule includes the style in which the definition is framed as well

as its truthfulness.  Figurative expressions should be avoided, too

great brevity may be obscure, just as prolixity may confuse.  Tautology

is a fault to be shunned.  Thus to define a parallelogram as "A four -

sided figure whose opposite sides are parallel and equal" would be

tautological ... the insertion of the words "and equal" leaves, and

indeed leads, a reader to suppose that there may be a four -sided

figure whose opposite sides are parallel and not equal.  Much is often

inferred in this manner which was by no means in the Author's mind;

thus, he who says that it is a crime for people to violate the property

of a humane landlord who lives among them, may perhaps not imply that

it is no crime to violate the property of an absentee landlord, or of

one who is not humane; but he leaves an opening for being so

Many attempts at definition fail because they do not name the genus.

It is no definition to say, 'So and so is a thing which' or 'So and so is

when', etc.  'A thing' and 'when' do not state the genus and lead nowhere.

At school, most of us learned that 'a noun is the name of anything', but this

definition fails to give the genus, for it does not make clear that a noun is

a word.  How should we define the word 'rock'?  'A rock is anything which

forms part of the earth's crust' fails because it does not name the genus.

But 'A rock is a material substance which forms part of the earth's crust'

would be a correct definition.

The first rule of definition is:

'A definition should not contain more than the connotation of the term

in question' (Venn).

Suppose I were to define a student as 'A human being residing in an

educational institution, and devoted to the pursuit of knowledge', I should

violate this rule.  The undue limitation of the class by the quality

'residing in an educational institute' makes the definition worthless.

A further rule is:

'A definition should not contain less than the full connotation'

The following is an example of failure to observe this rule: 'A map is

a representation of some part of the universe'.  This definition fails in two

respects: it lacks the word pictorial and unnecessarily includes too much,

namely, 'the universe':