Does Vagueness Involve Ignorance?

Let us identify our first dispute:

Ignorance: Does borderlineness exclude knowledge?

A positive answer to this question has for a long time simply been taken for granted: that if Harry is a borderline case of baldness then one can’t know whether Harry is bald.

On what side of this debate do the supervaluationist and epistemicist fall? Let us beginwiththe slogans. Epistemicismis notoriousfor makingapairofcounterintuitive claims. According to epistemicism there’s a nanosecond during which I stopped being a child, and nobody knows (or could come to know) when that nanosecond occurred. It is often suggested that this consequence of epistemicism is particularly outrageous, and that an alternative, such as supervaluationism, must be sought in its place. But a little inspection reveals that supervaluationism does no better in this regard. We have shown earlier that classical logic alone commits us to the existence of this critical nanosecond.^[24] But once this is accepted, the only point at which we can disagree with the epistemicist is over whether it is known (or possibly known) when that last nanosecond occurred. To disagree here is to maintain that not only is there a last nanosecond during which I was a child, but it is furthermore known (or at least possible to know) when this nanosecond occurred. Questions quickly multiply: if it is known, then by whom is it known? How was it discovered? If it is merely possibly known, how does one go about discovering it? Of course supervaluationists are no better positioned to answer these questions than anyone else, and most supervaluationists therefore agree with the epistemicist that we don’t and can’t know where the cutoff points are in sorites sequences.

One might think that while epistemicists and supervaluationists agree about the relation between borderlineness and ignorance, only the epistemicist identifies vague­ness with ignorance.

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