PHIL 1230 Lesson 3 — Complete Review

What is a valid argument?

An argument where true premises make a false conclusion impossible.

What does validity guarantee?

That if the premises are true, the conclusion cannot possibly be false.

Does validity require actual true premises?

No, validity is purely about logical structure, not actual truth.

What is a counterexample to validity?

A possible scenario where all premises are true and the conclusion is false.

How do you show an argument is invalid?

By providing a logically possible counterexample.

Can a valid argument have false premises?

Yes, valid arguments can have false premises and false conclusions.

Can a valid argument have a false conclusion?

Yes, if at least one premise is false.

What is the only combination forbidden by validity?

True premises and a false conclusion.

What is Modus Ponens?

If P then Q; P; therefore, Q.

Give a Modus Ponens example.

If P then Q; P; therefore, Q.

What is Modus Tollens?

If P then Q; not-Q; therefore, not-P.

Give a Modus Tollens example.

If raining, wet; not wet; therefore not raining.

What is Hypothetical Syllogism?

If P then Q; if Q then R; therefore, if P then R.

What is Disjunctive Syllogism?

P or Q; not-P; therefore, Q.

What is Affirming the Consequent?

If P then Q; Q; therefore, P. Invalid.

What is Denying the Antecedent?

If P then Q; not-P; therefore, not-Q. Invalid.

What is Constructive Dilemma?

P or Q; if P then R; if Q then S; therefore, R or S.

What defines a formal argument form?

A pattern of reasoning defined by structure rather than content.

Are circular arguments valid?

Yes, an argument whose conclusion is one of its premises is valid.

Why are circular arguments considered valid?

Because true premises and a false conclusion remain strictly impossible.

What happens if an argument has an impossible premise?

Yes, it is automatically valid.

Why do inconsistent premises make an argument valid?

Because it is impossible for all premises to be true simultaneously.

What happens if an argument has a necessarily true conclusion?

Yes, it is automatically valid.

Why does a necessary conclusion make an argument valid?

Because the conclusion can never be false under any circumstances.

Is validity about good persuasion?

No, logical validity does not guarantee a good real-world argument.

What is a sound argument?

A valid argument with actually true premises.

Can a valid argument be unsound?

Yes, if one or more premises are false.

Does validity depend on the subject matter?

No, validity depends entirely on logical form, not content.

What does an invalid argument fail to guarantee?

That the conclusion is true when premises are true.

What is the technical term for valid arguments with true premises?

A sound argument.