I will take two criteria which have been suggested, namely, (1) self-evidence, (2) mutual coherence.
(1) Self-evidence.--Some of our beliefs seem to be peculiarly indubitable.
If this theory is to be logically tenable, self-evidence must not consist merely in the fact that we believe a proposition.
Now symbols, in mathematics, mean what we choose; thus the feeling of self-evidence, in this case, seems explicable by the fact that the whole matter is within our control.
Their self-evidence, if this is so, lies merely in the fact that they represent our decision as to the use of words, not a property of physical objects.
Judgments of perception, such as "this buttercup is yellow," are in a quite different position from judgments of logic, and their self-evidence must have a different explanation.
It is unlikely that our two buttercups have EXACTLY the same colour, and if we judged that they had we should have passed altogether outside the region of self-evidence. To make our proposition more precise, let us suppose that we are also seeing a red rose at the same time.
For such reasons, no form of self-evidence seems to afford an absolute criterion of truth.