PHIL 250: Introduction to Symbolic Logic

tennant.9@osu.edu

---

Choose Destination My web-page Teaching PHIL 250 PHIL 650 Basic concepts and techniques Truth tables Universal-Introduction Universal-Elimination Existential-Introduction Existential-Elimination Negation-Introduction Negation-Elimination Conjunction-Introduction Conjunction-Elimination Disjunction-Introduction Disjunction-Elimination Conditional-Introduction Conditional-Elimination Absurdity rule Classical reductio Double negation elimination Law of Excluded Middle Dilemma

---

INTRODUCTION RULE FOR DISJUNCTION (∨I)

---

A ________ A∨B

B ________ A∨B

Explanation in words: In order to infer to a disjunctive conclusion A∨B, it is enough to prove either the disjunct A or the disjunct B. By taking either of the indicated steps of disjunction introduction, one thereby rests the disjunctive conclusion A∨B on the same assumptions on which the disjunct in question above the line rested.

Compare the corresponding elimination rule for ∨

---

[¬I] [∧I] [∨I] [→I] [∀I] [∃I]
[¬E] [∧E] [∨E] [→E] [∀E] [∃E]
[EFQ]
[LEM] [Dil] [CR] [DNE]

---