Descartes, working in solitude, could doubt all he wanted. Yet no one ever starts with doubt, because no one ever starts alone.
A child's first words are not his own. He imitates what he can. The act of speaking is a matter of desire and trust, that is, a desire to be like those whom I trust. If I cannot imitate others, I cannot express myself. That is the paradox.
But not just any others. For the child who is just learning to speak, mother and father are everything. The word for mother is their word for mother, and the word for father their word for father. This trust--this unique, exclusive, trust--exists before there are any words. The meaning of those words relies on that trust.
I wonder when it was that I first heard the word true. Most words a child learns are things you can point to, then things you can describe using words that name things you can point to. Can you point to truth? In the same way you can point to different colors, I suppose you can point to truth. Just as each object has a color, so each statement has a measure of truth or falsehood. So each of us most likely learns what truth means by example.
One's parents are not the only ones who explain what words mean. Trust is everything at that beginning phase, but that trust does not remain exclusive for so long. In my own experience, I seem to remember quickly sensing that truth was far beyond the control of just my parents, my teachers, or anyone else standing in authority over me. (I've heard this is consistent with my "INTJ" type on the Myers-Briggs.) But where on earth would that idea come from? The only way I ever knew the meaning of truth was by hearing others judge whether or not statements were true or false. I suppose it was natural that I would desire to imitate them in doing so. Thus the criteria I used must have been the same as theirs. If we can all agree what the word "blue" means by looking at the sky, surely we can also agree what truth is.
I've asked a lot of questions since then about what truth is. For a good time, I occasionally argue with someone who holds that absurd opinion that all truth is relative. Just as colors depend on culture and personal perspective--a culture that lives in areas where it snows all the time might have several words for "white," for example--so does truth. Or say they tell me. Perhaps we should all learn as many different languages as possible, just to prove that the relativists have no point here. Of course range of expression depends highly on culture and experience, but that doesn't mean truth itself is culturally dependent. On what culture (or personal perspective?), I wonder, does the statement that "all truth is relative" depend?
But I will concede that any capacity to know the truth is dependent on others. That is why philosophy done from an armchair only gets so far. It certainly shouldn't pretend to get all the way back to first principles. Whether we wish it or not, we are all stuck in the middle of the story.