Deductive Reasoning & Syllogisms
Chapter concept map
Tap a node with a dot to see its explanation.
Key formulas
Contrapositive
P → Q ≡ ¬Q → ¬P (Always valid)
Converse Fallacy
P → Q ⟹ Q → P ✗ (NOT valid — common trap)
De Morgan's Laws
¬(P ∧ Q) ≡ ¬P ∨ ¬Q ¬(P ∨ Q) ≡ ¬P ∧ ¬Q
Disjunctive Syllogism
P ∨ Q and ¬P → Q must be TRUE
Necessary vs Sufficient
'A is necessary for B' ≡ B → A 'A is sufficient for B' ≡ A → B
Subtopic 1 / 3
Contrapositive & Conditional Fallacies
From P → Q, only one inference is always valid:
Two fallacies that are NOT valid:
⚡ These two fallacies are the most tested traps in the Bocconi logic section. Every conditional question, ask: "Is this the contrapositive, or am I being asked to commit the converse fallacy?"
Worked example
"If R&D increases, profit margin expands." Contrapositive (valid): If profit margin did NOT expand → R&D did NOT increase. Converse (trap): If profit margin expanded → R&D increased. This does NOT follow — other things could cause profit growth. Inverse (trap): If R&D did not increase → profit margin won't expand. Also doesn't follow.
Exam strategy
Focus on understanding underlying concepts — exam questions test application, not memorization.
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