| Chapter 16: Understanding |

| 16.15. Context: understanding when

We have now seen several different forms of "Understand" sentence: for instance,

> Understand the colour property as describing a building block.
> Understand "mix [colour] paint" as mixing paint.
> Understand "rouge" as red.
> Understand "curious girl" as Alice.

Any of these may optionally have a condition tacked on: for instance,

> Understand "mix [colour] paint" as mixing paint when the location is the Workshop.
> Understand "rouge" as red when the make-up set is visible.

In principle, "when ..." can take in any condition at all. In practice a little care should be exercised not to do anything too slow, or which might have side-effects. (For instance, referring the decision to a phrase which then printed text up would be a bad idea.) Moreover, we must remember that the "noun" and "second noun" are not known yet, nor do we know what the action will be. So we cannot safely say "when the noun is the fir cone", for instance. If we want more sophisticated handling of such cases, we need to write checking rules and so on in the usual way.

Contexts can be useful to make sense of things having different names depending on who is being spoken to, as here:

> Understand "your" as a thing when the item described is held by the person asked.

With this rule in place FRODO, GIVE ME YOUR RING means that Frodo will know which ring is meant, even if there are a couple of dozen other rings present.

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| Example Bibliophilia A bookshelf with a number of books, where the player's command to examine something will be interpreted as an attempt to look up titles if the bookshelf is present, but otherwise given the usual response.

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