Wowee! I didn't think my humble question would ignite this kind of debate. Good job to all who have participated!
It seems to me that there is no such thing as exact
knowledge only agreed upon knowledge. Everything around us, and inside us for that matter, is a construct of our senses. If we were to discover or create new senses, reality as we now know it could change. Same goes if we lose senses.
We all take for granted that up is up and down is down, the sky is blue, and so on. But take away one sense and it all changes. We have our basic 5 senses. But how do you explain a blue sky to a blind man? You can use words, atmospheric chemistry, and even wavelengths of light, but that doesn't make it blue
in the sense that seeing it does.
We also have some other senses (no, not ESP) such as sense of balance, common sense, sense of danger (fight or flight), etc. Any pilot will tell you that it is easy to lose your sense of up and down. So what is up and what is down? It all comes down to language, and all language is fabricated by man to describe the world around us.
So I suppose this all makes me a relativist, but in the end everything is relative to the person observing it...so I may not even know what I'm talking about.