Chapter 1 Definitions

Question 1

Argument

Answer 1

An argument is a set of two or more sentences, one of which is designated as the conclusion and the others as the premises.

Question 2

Logical validity

Answer 2

An argument is logically valid if and only if it is not possible for the premises to be true and the conclusion false. An argument is logically invalid if and only if it is not logically valid.

Question 3

Logical soundness

Answer 3

An argument is logically sound if and only if it is logically valid and all its premises are true. An argument is logically unsound if and only if it is not logically sound.

Question 4

Logical truth

Answer 4

A sentence is logically true if and only if it is to possible for the sentence to be false.

Question 5

Logical falsity

Answer 5

A sentence is logically false if and only if it is not possible for the sentence to be true.

Question 6

Logical indeterminacy

Answer 6

A sentence is logically indeterminate if and only if it is neither logically true nor logically false.

Question 7

Logical equivalence

Answer 7

Sentences p and q are logically equivalent if and only if it is not possible for one of these sentences to be true while the other sentence is false.

Question 8

Logical consistency

Answer 8

A set of sentences is logically consistent if and only if it is possible for all the members of that set to be true. A set of sentences is logically inconsistent if and only if it is not logically consistent.

Question 9

Logical entailment

Answer 9

A set of sentences logically entails a sentence if and only if it is impossible for all the members o the set to be true and that sentence false.