In contemporary English usage, the word “evidence” is much narrower than “what makes something known” or “what makes something true”. We don’t tend to talk about the evidence for the rules of logical inference, mathematical theorems or postulates (like systems of numbers or the divisibility of lines), or truths that we have some reason to take for granted (fidelity of spouses, equality of the races, the value of democracy or peer review). While we can ask for evidence of truths that arise from practice, experience, and the testimony of experts, we usually don’t see the need, and it is not always possible.
Demands for evidence therefore involve both a restriction of an object to a domain that is more narrow than what is true, and is conditioned by a large background of things already evident. Asking about the value of free inquiry in an Aristocracy (where the proper place of everyone and orders of subordination are taken for granted) is a very different thing than asking about the transcendence of God in a democracy (where inequality is seen as the primary obstacle to overcome). Even under this restriction, evidence is widely varied and, if we want it to have the sort of clarity that it has in the courts, we need to rely on a good deal of positive law and judicial fiat. Even then, ambiguities will remain: were Fuhrman’s comments about blacks evidence for the defense? Were they exculpatory or simply inflammatory? Were they the heart of the trial or a distraction from it?
The application to arguments about God or the spirituality of mind is clear: it’s not clear whether “evidence” in our contemporary sense is relevant or a distraction. Assume it’s true: is the Ontological Argument evidence that God exists? It’s not an exhibit entered into evidence or Eddington measuring the bending of light in an eclipse or some fact that is a sign of something other than itself (the bloody glove behind Kato’s bungalow). Metaphysics simply doesn’t work like that. If we had a good argument why all truths needed to be based on evidence (like my friend’s argument that all reasoning is Bayesian) we might conclude that metaphysics was pseudo-knowledge; if we had a good argument why proving “God exists” is methodologically identical to proving that dark matter exists we might also prove the same thing. But it’s hard to see how a proof for God’s existence would work if we were asked to make “God” be a value that was operationally defined in terms of meters, seconds, or grams.
Given the restricted domain of evidence among things that we can know to be true, a complaint about the absence of evidence for God and the soul or a desire to offer such evidence is either a non sequitur or a failure to get the point. My suspicion is that this is true even where some religions make historical or factual claims. Evidence against Mohammed flying on a horse is just as much evidence that the tale ought to be read in a spiritual sense as proof that the religion itself contains falsities, and willingness to posit a spiritual sense is a more honest approach than other worldviews allow. There is certainly nothing like the spiritual sense to deal with the paradoxes and less-than-perfectly-empirical claims of, say, secular or communist morality.