Rules for Definitions

Logicians have identified six rules for constructing a type of definition that is suitable for general purposes.

A definition should:

1.   Include a genus and a differentia.
2.   Be neither too broad or too narrow.
3.   State the essential attributes of the concept's referents.
4.   Avoid circularity.
5.   Avoid negative terms.
6.   Avoid vague, obscure, and metaphorical language.

Let us examine each of these in turn.

Comprehension Questions

1.  Which rule does the following definition violate?

A chemical bond is the sharing of electrons between two or more molecules.

a) it doesn't include a genus and a differentia
b) it is too broad
c) it is too narrow
d) it doesn't state the essential attributes of the referents
e) it is circular
f) it uses negative terms unnecessarily
g) it uses vague, obscure or metaphorical language
2.  Which rule does the following definition violate?

Atoms are the type of matter than cannot be further subdivided.

a) it doesn't include a genus and a differentia
b) it is too broad
c) it is too narrow
d) it doesn't state the essential attributes of the referents
e) it is circular
f) it uses negative terms unnecessarily
g) it uses vague, obscure or metaphorical language
3.  Which rule does the following definition violate?

Radioisotopes are substances that are radioactive.

a) it doesn't include a genus and a differentia
b) it is too broad
c) it is too narrow
d) it doesn't state the essential attributes of the referents
e) it is circular
f) it uses negative terms unnecessarily
g) it uses vague, obscure or metaphorical language
4.  Which rule does the following definition violate?

Gastrin is a hormone that regulates digestion in human beings.

a) it doesn't include a genus and a differentia
b) it is too broad
c) it is too narrow
d) it doesn't state the essential attributes of the referents
e) it is circular
f) it uses negative terms unnecessarily
g) it uses vague, obscure or metaphorical language
5.  Which rule does the following definition violate?

Electrons have much less mass than protons or neutrons.

a) it doesn't include a genus and a differentia
b) it is too broad
c) it is too narrow
d) it doesn't state the essential attributes of the referents
e) it is circular
f) it uses negative terms unnecessarily
g) it uses vague, obscure or metaphorical language
6.  Which rule does the following definition violate?

Colloidal dispersions have particles that don't settle out.

a) it doesn't include a genus and a differentia
b) it is too broad
c) it is too narrow
d) it doesn't state the essential attributes of the referents
e) it is circular
f) it uses negative terms unnecessarily
g) it uses vague, obscure or metaphorical language
7.  Which rule does the following definition violate?

Selectively permeable membranes are bouncers who check IDs and only let certain individuals into an establishment.

a) it doesn't include a genus and a differentia
b) it is too broad
c) it is too narrow
d) it doesn't state the essential attributes of the referents
e) it is circular
f) it uses negative terms unnecessarily
g) it uses vague, obscure or metaphorical language

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