Why evidentialism is tantamount to scepticism

Over on Facebook, Carl Sachs offers a send-up of evidentialist reasoning. In the comments, I boil the argument down to this:

  1. Only believe on the basis of univocally sufficient evidence.
  2. Evidence is never univocally sufficient.
  3. Therefore, don’t believe!

It’s valid, but are the premises true?

Premise 1 is the principle of strict envidentialism famously defended by William Clifford.1 I’ve added the word “univocally” to capture the evidentialist’s idea that evidence determinately supports some claims and not others. They hold that there isn’t room for personal variation or disagreement over whether it does or doesn’t.2

Premise 2 is the upshot of much 20th-century philosophy of science. There is no single, precise solution to the problem of induction. Every strategy of learning from experience applies only contingently, so using one strategy rather than another necessarily involves risks. And there is no a priori rule for how to reckon with those risks.

Clifford himself was not a sceptic, but he rejected premise 2. Here’s what he says to evade the problem of induction:

We… add to our experience on the assumption of a uniformity in nature; we may fill in our picture of what is and has been, as experience gives it us, in such a way as to make the whole consistent with this uniformity.

Lots of scientists and philosophers have thought that the problem of induction could be dissolved by positing a Principle of the Uniformity of Nature (PUN). So it was a sensible thing for Clifford to write in the late 19th-century, I guess.3

Yet this stratagem is undone by 20th-century philosophy. There is no satisfactory way to specify the content of PUN. It is not enough to say that nature is uniform, because there are countless ways in which it is not. The future resembles the past in some respects but not in others. The problem is precisely to say which uniformities will hold and which won’t.4 Any answer involves speculation and risk.

Although I understand why Clifford could accept premise 1 without seeing that it leads to the conclusion, the case for premise 2 is now too strong to resist.5 So I don’t see how contemporary evidentialists can accept premise 1 without scepticism.

  1. In his 1877 essay “The Ethics of Belief”, perhaps best known as the foil for William James’ 1896 lecture “The Will to Believe”.
  2. They might allow that the boundary between support and non-support is vague, just so long as that vagueness holds in the same way for everybody.
  3. One might object that PUN can never be established by sufficient evidence, so believing it violates premise 1. This can be answered by allowing that Clifford is committed to premise 1 for all beliefs besides PUN.
  4. This is Goodman’s New Riddle of Induction, and the problem was raised at about the same time by Popper.
  5. One might reply: If premise 2 is true, what does it even mean for a case to be “too strong to resist”? This zinger reply won’t save the evidentialist, so I won’t try to answer it here.

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