18 lines
682 B
Markdown
18 lines
682 B
Markdown
---
|
|
tags:
|
|
- propositional-logic
|
|
- logic
|
|
---
|
|
|
|
# Disjunction Introduction
|
|
|
|
This rule can seem a little odd: like we are randomly introducing an additional
|
|
proposition without giving any justification. However this is just a consequence
|
|
of the fact if $P$ is true, so is $P \lor Q$ since disjunction is not the same
|
|
as conjunction: only one disjunct needs to be true for the compound disjunction
|
|
to be true. This is represented in the context of
|
|
[truth-trees](Truth-trees.md#disjunction-decomposition) by the fact that truth
|
|
can pass up via either branch of a disjunction pattern. This rule is sometimes
|
|
also referred to (confusingly) as _Addition_.
|
|
|
|
|