Nature and Scope of Logic
What this domain tests
This unit tests the definition of logic, the science/art distinction, the relation of logic to psychology and ethics, and the deductive–inductive divide. Expect short-answer items asking you to define logic, justify why logic is called a normative science, and classify given arguments.
Core ideas
- Logic is the science of the principles of valid inference - it studies the form of reasoning, not its subject matter.
- As a science, logic systematises the laws of inference; as an art, it trains the skill of correct reasoning.
- Logic is normative: it prescribes how we ought to reason. Psychology is descriptive: it records how we actually think. This is the standard reply to "Is logic a branch of psychology?"
- Formal (pure) logic studies inference patterns abstractly; material (applied) logic examines reasoning within a subject matter such as science or law.
- Deduction claims the conclusion follows necessarily; induction claims it follows probably.
Worked example
"All metals expand when heated; copper is a metal; therefore copper expands when heated." The content is chemistry, but the form is "All M are P; S is M; therefore S is P." The inference is deductive: if the premises are true, the conclusion cannot be false. Contrast "The sun has risen every morning so far; therefore it will rise tomorrow" - no amount of past data entails the prediction, so the argument is inductive and only probable.
Traps that cost marks
Confusing validity with truth; calling every argument with a general premise deductive; treating a true conclusion as proof that the reasoning was good; describing logic as a descriptive science of thought.