---
categories:
  - Logic
tags: [derivation-rules]
---

# Negation Introduction

This is also known as _proof by contradiction_. You start with an assumption declared in a sub-proof. If you can derive a contradiction from this assumption (typically from the introduction of another proposition and its negation), then you are permitted to derive the negation of the auxiliary assumption in the main proof.

![](/_img/negate-intro.png)
