## Tree Tutorial 8 Modal Trees

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### Reading

A text like

Rod Girle [2000] *Modal Logics and Philosophy*

would definitely be a help here.

### Tutorial

[Modal logic is a vast area, what is being presented here is the briefest of glimpses through the shop window (a book like the Girle would help you go further).]

In modal logic, there are the additional symbols □ (necessary) and ◊ (possible) and, in the background, the notion of 'possible worlds'.