i do believe evolution, being observable is indeed a fact. the theory is the construct or model for the past events.
it is however based on the LAWS of genetics. we cannot call evolution a law, per se, because it produces many different results, and is not always predictable in a strict sense. the end results, combinatorially, are too many, and the out comes to varied.
it's possible for it to essentially stop (like with the great white shark), make erratic jumps, dead end with extinction, etc. there's just too many factors.