Formal Fallacies

Question 0

Undistributed middle

Answer 0

A proposition distributes a term when it asserts something about the entire class that the term designates. In a valid standard form categorical syllogism, the middle term must be distributed in at least one premise.

Question 1

Four terms

Answer 1

A categorical syllogism shows the relationships between three classes of things. Each class is picked out by a term of the syllogism. If there is a change in the meaning of the term in the course of an argument, the terms pick out four classes, not three. So, it is not a categorical syllogism.

A standard form categorical syllogism must contain exactly 3 terms, each of which is used in the same sense throughout the argument.

Question 2

Illicit process

Answer 2

A premise that asserts something about only some members of a class cannot validly entail a conclusion that asserts something about an entire class. Whenever a conclusion of a syllogism distributes a term that is undistributed in the premises, the syllogism is invalid.

Two forms: 1. Illicit major- When the major term is distributed in the conclusion but not in the major premise.

2. Illicit minor- When the minor term is distributed in the conclusion but not in the minor premise.

In a valid standard form categorical syllogism, if either term is distributed in the conclusion, then it must be distributed in the premises.

Question 3

Exclusive premises

Answer 3

No standard form categorical syllogism having two negative premises is valid.

Question 4

Drawing an affirmative conclusion from a negative premise

Answer 4

If either premise is negative, the conclusion must be negative.

Question 5

Existential fallacy

Answer 5

From two universal premises no particular conclusion may be drawn.