2.2 Tautology and Contradictions

By the end of this lesson, you will be able to explain what is a Tautology and Contradiction.

Lesson 1 of 4: Tautology and Contradiction

The dictionary defines Tautology and Contradiction as follows:

• Tautology: the saying of the same thing twice over in different words, generally considered to be a fault of style.
• Contradiction: a combination of statements, ideas, or features which are opposed to one another.

However, in Logic, these words have different meanings. Click on the video below to find out more.

https://www.youtube.com/watch?v=Ji2vr-9duPI

Tautologies and Contradictions

Lesson 2 of 4: What have I learnt?

Tautology

A tautology is a statement that is always true, no matter what the truth values of the variables,

If you construct a truth table for a statement and all of the values in the last column for the statement are true (T), then the statement is a tautology.

Example of the left shows that p ∨~p is a Tautology.

Contradiction

A contradiction is a statement that is always false, no matter what the truth values of the variables .

If you construct a truth table for a statement and all of the values in the last column for the statement are false (F), then the statement is a contradiction.

Lesson 3 of 4: Review Questions

A tautology is a statement that is always true no matter what the truth values of the variables in a Truth Table.

• False
• True
• Answer