Scientific method does not apply to proving negatives. Scientists believe something exists based on evidence. I do not have any evidence that any "truth" can be unknowable by the human mind. I do know that you can NEVER know if something is true without evidence. Empiricism is the path to truth.
Soliton, you’re like the three year old who has learned to constantly ask “WHY?” and consequently thinks himself to be just the most clever fellow around. You made an unqualified positive assertion and now you can’t back it up. Of course, you knew you couldn’t going in, but you figured yourself to be too clever a fellow to not be able to wiggle out. To wiggle out, you’re now saying that you believe something (that no truth exists beyond your comprehension) about which you have no evidence (no rational cause to believe), and that you should not be held to the same standard you insist on imposing on everyone else.
The ball remains in your court, and you can’t even clear the net.