# Valid arguments as tautologies

If the premises of a propositionally valid argument are tautologies, then its conclusion must be a tautology as well. If the premises of the argument are tautologies, then they are all true under every assignment of truth values to the sentence letters. A valid argument with true premises has a true conclusion.

## What is an example of a tautology?

Tautology is the use of different words to say the same thing twice in the same statement. ‘The money should be adequate enough‘ is an example of tautology.

## Is a valid formula a tautology?

The definition of tautology can be extended to sentences in predicate logic, which may contain quantifiers—a feature absent from sentences of propositional logic. Indeed, in propositional logic, there is no distinction between a tautology and a logically valid formula.

## What are 5 examples of tautology?

Here are some more examples of common tautological expressions.

• In my opinion, I think… “In my opinion” and “I think” are two different ways to say the same thing. …
• First and foremost. …
• Either it is or it isn’t. …
• You’ve got to do what you’ve got to do. …
• Close proximity.

## What are the 10 examples of tautology?

Tautologies From Famous Speakers

• “It’s no exaggeration to say the undecideds could go one way or another.” – …
• “Our nation must come together to unite.” – …
• “It’s deja vu all over again.” – …
• “They are simply going to have to score more points than the other team to win the game.” –

## Are tautologies sound arguments?

A tautology is not an argument, but rather a logical proposition. A logical argument may contain tautologies. To be a valid logical argument (using the traditional rules of predicate logic), not only do all of your statements need to be true, but the argument needs to prove the statement being argued.

## How do you validate arguments?

An argument is valid if the premises and conclusion are related to each other in the right way so that if the premises were true, then the conclusion would have to be true as well.

## Can you have a valid argument with contradictory premises?

But on a classical conception of validity, any argument with contradictory premises counts as valid, since it is impossible for all the premises of an argument with contradictory premises to be true, and so a fortiori impossible for the argument to have true premises and false conclusion.

## What is a tautological argument?

A tautological argument is otherwise known as a circular argument, that is, one that begins by assuming the very thing that is meant to be proven by the argument itself.

## What is a tautological statement?

2 logic : a statement that is true by virtue of its logical form alone A logical combination of sentences that is always true, regardless of the truth or falsity of the constituent sentences, is known as a “tautology.”—

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## How do you prove tautology?

If you are given any statement or argument, you can determine if it is a tautology by constructing a truth table for the statement and looking at the final column in the truth table. If all of the truth values in the final column are true, then the statement is a tautology.

## How do you prove logical theorem?

To prove a theorem you must construct a deduction, with no premises, such that its last line contains the theorem (formula). To get the information needed to deduce a theorem (the sentence letters that appear in the theorem) you can use two rules of sentential deduction: EMI and Addition.

## What are tautologies and contradictions?

A compound statement which is always true is called a tautology , while a compound statement which is always false is called a contradiction .

## Is P and not PA contradiction?

Third, let us continue with P and Q as above. The sentence “if [P and Not(P)], then Q” is always true, regardless of the truth values of P and Q. This is the principle that, from a contradiction, anything (and everything) follows as a logical conclusion.
P and Not(P)

P Not(P) P and Not(P)
T F F
F T F

## What is a contradiction example?

contradiction Add to list Share. A contradiction is a situation or ideas in opposition to one another. Declaring publicly that you are an environmentalist but never remembering to take out the recycling is an example of a contradiction.