Examples:

1. 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.)
2. 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.)

Convincing Others: Identify the term being defined. Identify the conditions in the definition. Find an item which meets the conditions but is obviously not an instance of the term.

Reference: Cedarblom and Paulsen: 182

Examples:

1. An apple is something which is red and round. (Golden Delicious Apples are apples. However, they are not red (they are yellow). Amazing how some definitions can be both too narrow and too broad at the same time! See Example i above.)
2. 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.

Convincing Others: 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.

Reference: Cedarblom and Paulsen: 182

Examples:

1. 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.)
2. An object is beautiful if and only if it is aesthetically successful. (The term "aesthetically successful" is harder to understand than the term "beautiful.")

Convincing Others: 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.

Reference: Cedarblom and Paulsen: 184

Examples:

1. An animal is human if and only if it has human parents. (The term being defined is "human." But 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.)
2. 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.)

Convincing Others: 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.

Reference: Cedarblom and Paulsen: 184

Examples:

1. A society is free if and only if liberty is maximized and people are required to take responsibility for their actions. (If a person is required to do something, then that person's liberty is not maximized.)
2. 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 he/she has "no previous driving experience.")

Convincing Others: 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).

Reference: Cedarblom and Paulsen: 186