"But let us never forget, either, as all conventional history of philosophy conspires to make us forget, what the 'great thinkers' really are: proper objects, indeed, of pity, but even more, of horror."
David Stove's "What Is Wrong With Our Thoughts" is a critique of philosophy that I can only call epic.
The astute reader will of course find themselves objecting to Stove's notion that we should be catologuing every possible way to do philosophy wrong. It's not like there's some originally pure mode of thought, being tainted by only a small library of poisons. It's just that there are exponentially more possible crazy thoughts than sane thoughts, c.f. entropy.
But Stove's list of 39 different classic crazinesses applied to the number three is absolute pure epic gold. (Scroll down about halfway through if you want to jump there directly.)
I especially like #8: "There is an integer between two and four, but it is not three, and its true name and nature are not to be revealed."
Saying that 2+2=4 is a tautology in a certain axiomatic system defined with '+' means that you couldn't have anything but 2+2=4 in that system. It's simply mandatory, and a rational person could not wake up one day and be convinced that 2+2=3 within a self-consistent system that deduces 2+2=4.
While tautological truth is independent of observation (let's call it mathematical truth), it is dependent upon context (i.e., a self-consistent axiomatic system). Some mathematical truths in one axiomatic system are false in another. When we talk about whether a a mathematical statement is true, we need to specify the context, and, in my opinion, in the most demanding definition of truth, the context is the real, actual, empirical world. So I agree with Eliezer that a mathematical tautology must be observed in order to be true.
When we humans talk about "2+2=4", it is because we have chosen arithmetic from an infinite number of possible axiomatic systems and given it a name and a set of agreed-upon symbols. Why did we do that? Because we observed arithmetic empirically. Obviously, addition is just one operation of infinitely many operations. The ones we have defined (multiplication, subtraction, addition mod n, taking the cardinality of subsets of, etc.) usually have some empirical relevance. While we don't feel very comfortable thinking of those that don't (and this says somethng about the way we think), I have faith that if we were presented with a very strange set of observations, it would take a pretty short amount of time to train ourselves to think of the new operation as a "natural" one.
... I idly wonder if there is a such thing as a mathematical truth that could not be realized empirically, in any context, and if there would be any way of deducing it's non-feasability.
Is saying "we could have a different axiomatic system" different from saying "2, 4, +, and = could all mean different things? Of course we've only defined the operations and terms that are useful to us. I don't care about the naturalness of '+' only that once I know the meaning of the operations and terms the answer is obvious and indisputable.
Math isn't my field, so my all means show me how I'm wrong.