Conditional Logic — Master This or Fail

If A, then B. A=sufficient, B=necessary.

Contrapositive: If NOT B, then NOT A. Always valid.

INVALID inferences:

If A then B does NOT mean if B then A (affirming the consequent)

If A then B does NOT mean if not A then not B (denying the antecedent)

Trigger words:

"If/when/whenever/every/all" → sufficient conditions

"Only if/requires/must/necessary" → necessary conditions

"Only if" is backwards: "You pass only if you study" = If pass, then studied. NOT if studied, then pass.

This logic appears in EVERY section. Non-negotiable skill.

Reference:

Wikipedia: Conditional Statement

https://en.wikipedia.org/wiki/Conditional_statement