What is Logic?
Logic is the study of valid reasoning — the rules that let us move from true premises to true conclusions. It underlies mathematics, science, law, and everyday argument.
Logic is the systematic study of correct reasoning, distinguishing valid arguments (where the conclusion must follow from the premises) from invalid or fallacious ones.
- •General → specific
- •Conclusion guaranteed if premises are true
- •Example: All men are mortal; Socrates is a man; so Socrates is mortal
- •Used in mathematics and formal logic
- •Specific → general
- •Conclusion only probable, not certain
- •Example: Every swan I've seen is white; so all swans are probably white
- •Used in science and everyday reasoning
Step-by-step worked examples
Evaluate this argument: 'All birds can fly. Penguins are birds. Therefore, penguins can fly.' Is it valid or sound?
The argument is logically VALID — the conclusion follows the form (All A are B; C is A; so C is B). But it is NOT SOUND, because the first premise 'All birds can fly' is factually false (penguins can't fly). A valid argument with a false premise can still have a false conclusion.
Classify this reasoning: 'The sun has risen every day of recorded history, so it will rise tomorrow.'
This moves from many specific observations to a general prediction — this is INDUCTIVE reasoning. Unlike deduction, the conclusion is highly probable but not logically certain. Inductive arguments are evaluated by strength, not validity.
Identify the fallacy: 'You're wrong about climate change because you're not a scientist.'
This attacks the arguer's credentials instead of the argument's content. This is the fallacy of AD HOMINEM (attacking the person). The truth of a claim doesn't depend on who states it.
Flashcards
Quick quiz
Q1.Which best defines a valid deductive argument?
Q2.'All cats are mammals. Fluffy is a cat. Fluffy is a mammal.' What type of reasoning is this?
Q3.A valid argument with a false premise is:
Q4.Attacking a person instead of their argument is called:
The full card deck, worked steps and AI-tutor support for “What is Logic?” are in Notek — study by hand before your exam.
Common mistakes
Valid means the conclusion is true. — Correct: Valid only means the conclusion follows logically from the premises — it can still be false if a premise is false.
Inductive reasoning gives certain conclusions. — Correct: Inductive reasoning gives probable conclusions, never logical certainty.
A persuasive argument is automatically logical. — Correct: Persuasion can rely on emotion or rhetoric with no logical validity at all.
All fallacies make an argument's conclusion false. — Correct: A fallacy makes the reasoning bad, but the conclusion could still happen to be true.
FAQ
What is logic?
Logic is the study of principles of correct reasoning, distinguishing valid arguments from invalid ones.
What is the difference between deductive and inductive logic?
Deductive reasoning guarantees the conclusion if premises are true; inductive reasoning only makes it probable.
What are examples of logical fallacies?
Common ones include ad hominem, straw man, false dilemma, and circular reasoning.
How is logic used in daily life?
It underlies debate, decision-making, coding, math proofs, and evaluating news claims.