Syllogisms with a self-contradictory premise are always valid. Syllogisms with a self-contradictory conclusion are valid **if and only if their premises contradict each other**.

## Can an argument with contradictory premises valid?

Well, if the premises are contradictory, then they cannot all be true (that’s just what contradictory means) so they can’t all be true while the conclusion is false (the necessary condition for non-validity). So the argument cannot be non-valid, it must be valid. Thus **an argument with contradictory premises is valid**.

## Can a valid syllogism have false premises?

**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.

## What makes a syllogism valid or invalid?

**A valid syllogism is one in which the conclu- sion must be true when each of the two premises is true**; an invalid syllogism is one in which the conclusions must be false when each of the two premises is true; a neither valid nor invalid syllogism is one in which the conclusion either can be true or can be false when …

## Can there be a valid argument whose conclusion is a contradiction?

This implies that the conclusion is a tautology. Therefore, if the premises of a propositionally valid argument are tautologies, then its conclusion must be a tautology as well.

No propositionally valid argument can have a contradiction as a conclusion.

P | (P∧¬P) | ¬(P→P) |
---|---|---|

T | F | F |

F | F | F |

## Why are contradictory premises valid?

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.

## Can you render an invalid argument valid by removing premises?

**In classical logic no, but you can make a sound argument unsound by adding false premises**. The difference between soundness and validity is usually ignored colloquially, but logical validity is neutral on the truth of the premises, it only cares whether inference would preserve that truth.

## Can premises be valid?

TRUE: **If an argument is sound, then it is valid and has all true premises**. Since it is valid, the argument is such that if all the premises are true, then the conclusion must be true. A sound argument really does have all true premises so it does actually follow that its conclusion must be true.

## Can a valid syllogism have false premises quizlet?

**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. … Since a sound argument is valid, it is such that if all the premises are true then the conclusion must be true.

## Can a syllogism be false?

Valid: A deductive argument is said to be valid if it is impossible for the conclusion to be false if the premises are true. If the conclusion logically follows the premises, the syllogism is valid. **A syllogism can be valid but not sound**: All birds can fly.

## Can a contradiction entail any statement?

The schema is (roughly) that whenever P entails a contradiction, P is false. That’s shorthand for saying that **whenever a statement entails a contradiction, the statement can’t be true**. In other words, Pick any “real life” statement you like that entails a contradiction.

## 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.

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

Think hypothetically. **Ask, “IF the premises are true, are we locked into the conclusion?” If yes, then the argument is valid.** **If no, then the argument is invalid**.

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

**All valid arguments have all true premises and true conclusions**. All sound arguments are valid arguments. If an argument is valid, then it must have at least one true premise. Every valid argument is a sound argument.

## Could there be a valid argument that has one false premise and one true premise?

**No, the conclusion of an valid argument could be true or false**. We only know that in either case it will be impossible for it to have all true premises and a false conclusion.