Deductive Reasoning
📋 What it is
Deduction goes from a general rule to a certain conclusion about a specific case.
🗣️ Coach says
Deduction is the “sure” kind of reasoning. If the rule is true and your case fits it, the conclusion MUST be true. “All squares have 4 sides; this is a square; so it has 4 sides.” No wiggle room.
🧠 Memory hook
DEDuce = work DOWN from a rule to a case. Rule true + fits = certain.
😂 Giggle
Why was the counterexample so annoying?
It only needed ONE case to ruin everything!
😲 Whoa!
Deduction is the only kind of reasoning that gives 100% certainty — which is exactly why mathematics is built on it.
✅ Quick check: “All multiples of 4 are even. 12 is a multiple of 4.” What can you conclude for certain?
Say your answer out loud first — then reveal.
12 is even — the rule applies to the case with no exceptions, so the conclusion is guaranteed.
Deduction from a true general rule to a fitting case yields certainty.
🧪 Try it! (2 minutes)
Pick a rule you know (“all triangles have 3 corners”) and apply it to 3 specific shapes. Notice you never had to check — the rule guaranteed it.