It's an often-observed irony that the more we know the less convinced we become that we can know anything. As children, we knew the grass was green and the sun was hot, and we were convinced that was the whole story; then we learned that the grass is green because it has chlorophyll cells in it, and the sun is hot because it's a giant ball of reactive gas. And then, if we really think about it, we realize that there is no such thing as "green" or "hot" in the first place, because "green" is just a neuron signal triggered by the eye's perception of a certain wavelength of light, and "hot" is likewise just the perception in the mind of nerve cells sensing the intensity of the movement of molecules in the area around the skin. That is to say, "green" and "hot" only exist in the sense that you perceive them; if you did not have eyes, then nothing would be green, and if your nerve cells could not react to temperature, then nothing would be hot.
Of course, dragging this to its logical end, one comes to the realization that everything we think of as truth is really just our perception of some sort of external Truth. Green is our perception of the external Truth (which we do not understand) that we call wavelengths of light, and hot is our perception of the external Truth that we call temperature. The same can be said of sight, touch, taste, smell, hearing, even logical thought: all are approximations of an external reality.
But this means that we fundamentally do not know Truth. We can perceive it, yes, assuming exists (refer to Solipsism), but our perception is not Truth. It is an approximation, and as such can only be described as flawed. Logic can be misunderstood or misapplied, language can be twisted, even our own physical senses can be unreliable (witness sight and touch, for example).
The implication is, then, that we cannot say with certainty if any individual something is true - that is, in line with the external Truth - because we do not know Truth, we only perceive it. Something can appear to us to be true - perhaps we even have an unshakable conviction that it is true - but we can never know for certain what, exactly, composes the external Reality.
Perhaps it is the closest to Truth we can come to say, in the words of Socrates however many thousands of years old, that we know that we do not know.
Intelligent discussion, as always, available in the comments section below.
