Logical Connectives to Know for Formal Logic I

Logical connectives are the building blocks of formal reasoning, allowing us to combine and manipulate propositions. Understanding these connectives—like negation, conjunction, and disjunction—helps in constructing clear arguments and proofs across various mathematical disciplines.

1. Negation (NOT)

   • Represents the opposite truth value of a proposition.
   • Symbolized by ¬ or ~; if P is true, ¬P is false, and vice versa.
   • Fundamental in constructing logical statements and proofs.

2. Conjunction (AND)

   • Combines two propositions; true only if both are true.
   • Symbolized by ∧; for propositions P and Q, P ∧ Q is true if both P and Q are true.
   • Essential for forming compound statements in logical reasoning.

3. Disjunction (OR)

   • Combines two propositions; true if at least one is true.
   • Symbolized by ∨; for propositions P and Q, P ∨ Q is true if either P, Q, or both are true.
   • Important for inclusive reasoning in logical arguments.

4. Conditional (IF-THEN)

   • Represents a relationship where one proposition implies another.
   • Symbolized by →; P → Q is false only when P is true and Q is false.
   • Key in understanding implications and logical deductions.

5. Biconditional (IF AND ONLY IF)

   • Indicates that two propositions are equivalent; both must be true or both must be false.
   • Symbolized by ↔; P ↔ Q is true if both P and Q share the same truth value.
   • Crucial for establishing equivalences in logical statements.

6. Exclusive OR (XOR)

   • True if exactly one of the propositions is true, but not both.
   • Symbolized by ⊕; for propositions P and Q, P ⊕ Q is true if either P or Q is true, but not both.
   • Useful in scenarios requiring distinct choices or outcomes.

7. NAND (NOT AND)

   • True unless both propositions are true; the negation of conjunction.
   • Symbolized by ↑; P ↑ Q is false only when both P and Q are true.
   • Important in digital logic and circuit design.

8. NOR (NOT OR)

   • True only when both propositions are false; the negation of disjunction.
   • Symbolized by ↓; P ↓ Q is true only if both P and Q are false.
   • Significant in logical operations and simplifications.

9. Material Implication

   • A specific form of conditional that relates truth values of propositions.
   • Often expressed as P → Q, where the truth of Q is contingent on P.
   • Fundamental in formal logic and proofs.

10. Sheffer Stroke

    • Represents a logical operation that combines negation and conjunction.
    • Symbolized by |; P | Q is true unless both P and Q are true.
    • Can be used to express all other logical connectives, making it a powerful tool in logic.