## How do you determine if an argument is valid or invalid?

**A deductive argument is said to be valid if and only if it takes a form that makes it impossible for the premises to be true and the conclusion nevertheless to be false**. Otherwise, a deductive argument is said to be invalid.

## How do you know if a truth table is invalid or valid?

In general, to determine validity, **go through every row of the truth-table to find a row where ALL the premises are true AND the conclusion is false**. Can you find such a row? If not, the argument is valid. If there is one or more rows, then the argument is not valid.

## What is a Tautologous conclusion?

A valid argument with true premises has a true conclusion. So, **the conclusion of a valid argument with premises that are tautologies is also true under every assignment**. This implies that the conclusion is a tautology.

## Why every argument with a Tautologous conclusion is valid?

An argument whose conclusion is a tautology MUST be valid! **Since a tautology is always true an argument whose conclusion is a tautology never has a false conclusion**. But if the conclusion of the argument is NEVER false, then there cannot possibly be an invalidating row, so the argument must be valid.

## Can an invalid argument have true premises and true conclusion?

If an argument has all true premises and a true conclusion, then it is valid. FALSE: **It is possible for an argument to have all true premises and a true conclusion but still be invalid.**

## Can a valid argument have false premises and a true conclusion?

**A valid argument can have false premises; and it can have a false conclusion**. But if a valid argument has all true premises, then it must have a true conclusion.

## When an argument is valid and its premises are true the argument is called?

More specifically, we ask whether the argument is either deductively valid or inductively strong. A **deductive argument** is an argument that is intended by the arguer to be deductively valid, that is, to provide a guarantee of the truth of the conclusion provided that the argument’s premises are true.