## Tuesday, May 27, 2014

### Explanation modulo a fact

A notion that I find rather natural is the idea of explanation modulo a fact. This notion can do some of the work that contrastive explanation can.

1. Why did you eat a banana?
can be precisified contrastively in ways like:
1. Why did you eat a banana rather than something else?
2. Why did you eat a banana rather than doing something else with it?
3. Why did you eat a banana rather than not eating anything?
But one can also accomplish the same thing this with requests for explanation modulo a fact. Doing the work of 2 and 3 is easy:
1. Given that you ate, why did you eat a banana?
2. Given that you did something with a banana, why did you eat it?
Doing the work of 4 is a bit harder, but maybe this works:
1. Given that you ate a banana if you ate anything, why did you eat a banana?

When we ask for explanation why p given q, we are asking for something that isn't just an explanation why q, and that gives us a further explanation why p when added to the fact taht q. The question presupposes there is such an additional truth. If the fact that q is the one and only complete explanation why p, then the question has a false presupposition.

It seems, however, that any request for explanation modulo a fact can be rephrased as a request for contrastive explanation. For instead of asking:

1. Given q, why p?