How could someone not know that \(1 + 4 = 2 + 3\)? Yet it happens for small children, and for us bigger children similar, but more complex, examples of mathematical truths we don’t know can be found. Obviously the designations of “\(1 + 4\)” and “\(2 + 3\)” are the same, so their senses must be different. But if we model sense by a function from states to designations, the functions would be the same, mapping each state to 5. If it is necessary truth that is at issue, there is no problem; we certainly want that \(1 + 4 = 2 + 3\) is a necessary truth. But if epistemic issues are under consideration, since we cannot have a possible world in which “\(1 + 4\)” and “\(2 + 3\)” designate different things, “\(1 + 4 = 2 + 3\)” must be a known truth. So again, how could one not know this, or any other mathematical truth?