Nature and Scope of Logic
Logic is the normative study of the principles that separate correct from incorrect reasoning. In the Assam HS Logic and Philosophy paper, this domain tests whether you can break an argument into premises and conclusion, distinguish validity from truth, classify inference as deductive or inductive, and recognise the scope of formal and informal logic.
Core rules
- An argument is a group of propositions in which some, the premises, are offered as support for another, the conclusion. A single statement or an explanation is not automatically an argument.
- Validity is formal: an argument is valid if it is impossible for all premises to be true while the conclusion is false. Truth applies to individual propositions; validity applies to argument form.
- Soundness means validity plus all true premises. A valid argument can have false premises and still be valid.
- Deduction claims conclusive support; induction claims probable support. Logic is normative, not a description of how people happen to think.
- Formal logic abstracts form from content; informal logic studies ordinary-language reasoning and fallacies.
Worked example
Premises: All mammals are warm-blooded; whales are mammals. Conclusion: whales are warm-blooded. The form is All M are W; all S are M; therefore all S are W. The form is valid. Because both premises are true, the argument is also sound. If the first premise were false, the argument would remain valid but cease to be sound.
Traps
Do not call a true conclusion valid; validity concerns the link between premises and conclusion. Do not treat a conditional sentence as an argument. Do not assume a false premise makes the form invalid. Inductive strength is a matter of degree, not simple truth or falsity.