forum 3: week of 23 Jan - Lewis II
In response to Ange's and Zack's objections, respectively. I don't see the rule of actuality making any normative 'ought-' claim because it is externalist.
As Lewis states, "the subject himself may not be able to tell what is properly ignored": the subject may ignore proposition p that obtains in the real world all he wants(provided his own normative epistemic conditions lead him to do that, and setting aside the other rules for the sake of brevity). But the fact that p is true means that it is not properly ignored. This rule captures the fact that in order to know that p, p has to be true in our world.
We are not deciding whether p is relevant, I don't think. To decide whether p is relevant is to make p a relevant alternative by including it into the conversation! That is what makes me think that this rule is for the most part descriptive.
Additionally, the rule is not saying that we can't(neither physically nor normatively) ignore the actual state of things. It is saying that if we ignore the actual state of things, we have gone wrong, because we cannot know what is untrue.
...If I've interpreted it correctly.