Some basic logical concepts — Truth, Validity, Inference, Implication

“All lawyers are liars. Raj is a lawyer. Therefore Raj is a liar.” The argument is airtight in structure — and the first premise is false. Is the argument good or bad? Your gut wants to say bad, because the conclusion is unfair. Logic forces you to separate two questions people constantly mix up: is the argument's structure valid, and is its content true?

In two minutes

Truth and falsity are properties of individual propositions; validity and invalidity are properties of an argument's structure; inference is the mental movement from premises to conclusion; and implication is the logical relation between propositions such that the truth of one guarantees the truth of the other.

The rest of this chapter

The full explanation, the cheat sheet, every previous-year question at every mark weight, the quiz and the answer skeletons are part of Logic – I on LexBlox Semester. Sign in to unlock the subject, or read Module 1 of Legal Language and Writing free.