There is endless conjecture, and certainty is not to be counted upon (Kant, Critique of Pure Reason)
Some people treat evidence as something that accumulates over time, like sap from a tree. Once enough evidence is collected, you need only synthesize it into syrup, and then you’ve proved your point. “I have X amount of evidence for Y, therefore you ought to believe Y, otherwise you are behaving irrationally.” So the story goes.
I don’t think there is such a thing as ‘evidence’, at least how it’s traditionally understood, since all corroborating evidence cannot say whether or not the theory is true or false. It’s the nature of the beast: The logical content of the set of corroborating evidence is always smaller than the theory the set is intended to corroborate.
When scientists test some particles in a lab to a high degree of accuracy, or take a volt meter and stick it on things, then they are said to be gathering ‘evidence’; however, scientists have only tested an extremely limited number of objects: Nobody has done tests on quantum mechanics of the ivory of piano keys, monkeys in the Congo, the pages of the Gutenberg bible, &c. Yet, QM is said to work just as well for my piano keys and chairs and rat brains and everything else that hasn’t been put under a direct test …
Even if all our tests are correct, our present theories may be a false limited case of a broader theory, the theory could be false in certain regions of space, during certain times, when applied to certain elements under specific stress, &c.
Assume for a moment that this ‘syrup’ theory of evidence is true. What does that mean when one encounters a falsifying/disconfirming/refuting test? Does the syrup evaporate in a flash of heat? If so, then the syrup serves no purpose. Does the syrup remain, but only reduced by a small bit? Then it contradicts the deductive inference of modus tollens.
Put that aside for a moment and consider a (relatively) recent amendment: instead of quantifying evidence, we quantify our belief in the evidence. How do we carry over this additive ‘syrup’ concept of evidence to apply to belief? Forgive me if I’m a bit incredulous, but it looks, at least to me, that it suffers from all the problems of quantifying evidence, along with all sorts of new problems.