"How about likelihood Master? Scientists must always guess or judge the likelihood of things not known yet."
"Indeed it is the very most important principle for science. Yet, it is not truth itself. It is mere maintenance of opinion until proved. Then it has become a True Word. About gods or sperrits, mermaids or centaurs, two possibilities (a pair) exist: 'is' and 'is not'. One may believe in one, which is opinion, is giving it a great likelihood, but it is only the PROOF that turns opinions into facts, into True Words. Facts are not open to the pair: Believing/Not-Believing.
"Are there not varieties in facts?"
"No. 'A fact is that what has happened', it is an absolute
truth. There are however semi-truths that are almost as true as
facts, the physical laws for instance. We live by the semi-truth
that gravitation will be tomorrow, yet, unlikely as it is, we
cannot 'know' until the day after." [13]