The problem of the criterion, which is discussed in Pyrrhonian skepticism, states that in order to determine whether a claim is true there needs to be an appeal to a criterion by which the veracity of this claim can be known.

However, once we call into question whether this criterion is that by which we can make this assessment, we fall into trouble. What are we to do?

First, we can double down and proceed by fiat, no longer by reason. This, of course, won’t do as we’re presently in the court of reason. Second, we can defend the criterion, only to discover that we’re engaged in circular reasoning: to regard A as a piece of evidence, we need to appeal to our criterion (call it “Y”); to make a case for the criterion Y, we need to adduce evidence A. Third, we can fall into a regress problem whereby criterion X stands behind criterion Y, which stands behind criterion Z, and so on.

In short, we’re in trouble–and such, in a word, has been the history of modernity as it’s unfolded since the Protestant Reformation. What ensued but the bloody wars of religion, the birth of toleration, and the subsequent hollowing out of religious life? For more:

We can find a solution to the skeptical problem of the criterion, I submit, by turning to Advaita Vedanta. In conversation with a young man, Sri Ramana Maharshi replies:

M[aharshi]: But this is not known in sleep. Now or then, the same you remain[s]. Who has changed now? Is your nature to be changing or remain unchanging?
D.: What is the proof?
M.: Does one’s own being require a proof? Only remain aware of
your own self, all else will be known

–Sri Ramana Maharshi, “Talk 478,” Talks With Sri Ramana Maharshi, p. 473.

What Ramana Maharshi offers is self-evidence: your own being requires no proof because it’s experientially self-revealing or self-evident.

If I were to ask you, “Are you conscious?,” you’d open directly to the experience of just being conscious. This self-evident experience–or direct experience of being conscious–is prior to doubt and thus is prior to proof. A proof suggests that something is to be inferred. But your very being is prior to rationality and yet, for all that, is not irrational. Being known immediately, it is self-shining.

There is, in the self-shining of your own being, no problem of the criterion. The problem simply cannot arise. Ultimately, you know your very being by being your very being. Herein lies the fundamental solution to this longstanding and corrosive epistemic doubt that has for so long been ailing us moderns…