But when we say S knows that p, we don't mean to quantify over all possibilities there are, only over the salient possibilities.
Justification, of course, comes in degrees; and what counts as justification simpliciter i.e., justification to the level required for an attribution of knowledge to express a truth is governed by a 'rule of salience' (1998, 292, n. 11), whereby one's evidence/reasons must be good enough to preclude salient possibilities of error.
The more salient that possibility, the more circumspect our thinking.
Therefore, relative to what we mean by 'know' when we are confronted with a salient error possibility such as being a BIV, we know neither that we have hands nor that we are not BIVs.
In terms of the first part of the strategy, this suggests that once we make salient the possibility of supernatural beings, specific supervenience theses that posit a naturalistic base become more doubtful.
So, when we are thinking about or discussing the BIV argument and are thus confronted with a salient error possibility, we need not adopt a high-standards meaning of 'know'know
Whereas, that I am a handless BIV is not ordinarily a salient counter-possibility to my having hands though perhaps my having had my hands amputated and replaced with prostheses after a bad car accident, e.g., is.
Romney's shift to the legal right should be especially salient given the possibility that the next president will choose Justice Ruth Bader Ginsburg's replacement.
When the sceptic starts talking about fantastic possibilities of error, she makes those possibilities salient.
This methodology makes salient the very real possibility that our best accounts of the reference of various different sorts of terms will prove to be difficult, if not impossible, to reconcile with each other.
