As usual, science has a more practical take on this. Occam's Razor says that if you see a cow shape and hear a cow sound coming from that direction, the most likely explanation is that you're seeing a cow. It retains the possibility this isn't true; the belief can be falsified in several ways: by examining the cow more closely, by the real cow walking out from being the fake one, etc.

I think it follows that we never absolutely "know" something. We asymptotically approach knowledge. The scientific method is a way of approaching truth.