# Rule of Material Implication/Definition

## Theorem

The Rule of Material Implication can be used as a definition for the logical operator that is implication:

$p \implies q := \neg p \lor q$

## Historical Note

This definition appears in the introductory material of 1910: Alfred North Whitehead and Bertrand Russell: Principia Mathematica: Volume $\text { 1 }$, and some other authors follow their lead.