Examples:

1. All dogs are animals. Cats are mammals. Thus, all dogs are mammals. (The premises and the conclusion are all true. But the logical rationale is flawed. The four terms are "dogs," "animals," "cats," "mammals.")
2. Only man is born free. No child is a man. Thus, no child is born free. (In this case, the fallacy of four terms is a special case of equivocation. While the same word is used, the word has different meanings. In the major premise, “Only man is born free,” "man" refers to "humanity." In the minor premise, “No child is a man,” "man" refers to "adult male." The four terms are "man (humanity)," "man (adult male)," "child" and "born free.")

Convincing Others: Identify the four terms and where necessary state the meaning of each term.

Reference: Copi and Cohen: 206

Examples:

1. All Russians were revolutionists. All anarchists were revolutionists. Therefore, all anarchists were Russians. (The middle term is "revolutionists." While both Russians and anarchists share the common property of being revolutionists, they may be separate groups of revolutionists. So, we cannot conclude that anarchists are otherwise the same as Russians in any way.)
2. All trespassers are shot. Someone was shot. Therefore, someone was a trespasser. (The middle term is "shot." While "someone" and "trespassers" may share the property of being shot, it doesn't follow that the someone in question was a trespasser; he may have been the victim of a mugging. This is an example from Copi and Cohen, 208.)

Convincing Others: Show how each of the two categories identified in the conclusion could be separate groups even though they share a common property.

Reference: Copi and Cohen: 207

Example:

1. All Texans are Americans. No Californians are Texans. Therefore, no Californians are Americans. (The predicate term in the conclusion is "Americans." The conclusion refers to all Americans — that is, "Every American is not a Californian." But, this same term in the major premise refers to only some Americans — that is, those that are Texans.)

Convincing Others: Show that there may be other members in the predicate of the conclusion that

1. are not mentioned in the major premise,
2. but that contradict the statement of the conclusion.

Reference: Copi and Cohen: 207

Example:

1. All communists are subversives. All communists are critics of capitalism. Therefore, all critics of capitalism are subversives. (The subject term in the conclusion is "critics of capitalism," and the conclusion refers to all such critics. However, the minor premise, “All communists are critics of capitalism,” refers to only some critics of capitalism; there may be other critics who are not communists.)

Convincing Others: Show that there may be other members in the subject of the conclusion that

1. are not mentioned in the minor premise,
2. but that contradict the statement of the conclusion.

Reference: Copi and Cohen: 208

Example:

1. No Manitobans are Americans. No Americans are Canadians. Therefore, no Manitobans are Canadians. (In fact, since Manitoba is a province of Canada, all Manitobans are Canadians.)

Convincing Others: Assume that the premises are true. Find an example that allows the premises to be true but clearly contradicts the conclusion.

Reference: Copi and Cohen: 209

Examples:

1. All mice are animals. Some animals are not dangerous. Therefore, some mice are dangerous.
2. No honest people steal. All honest people pay taxes. So, some people who steal pay taxes.

Convincing Others: Assume that the premises are true. Find an example that allows the premises to be true but clearly contradicts the conclusion.

Reference: Copi and Cohen: 210

Examples:

1. All mice are animals. All animals are dangerous. So, some mice are dangerous. (Actually, all mice are dangerous. Given the appropriate circumstances, any mouse can be dangerous.)
2. All trespassers today will be shot. No one will trespass this week. So, someone today will be shot.
3. No honest people steal. All honest people pay taxes. So, only some honest people pay taxes.

Convincing Others: A universal conclusion must follow from universal premises. A particular conclusion that follows from universal premises must not be taking all instances into account. Find one such instance.

Reference: Copi and Cohen: 210