Evolution is fact. That much should be beyond dispute, so long as we can all come to agreement on what the word “evolution” means. Unfortunately, therein lies the rub. In a 2001 paper, Stephen Meyer and Michael Keas ably lay out the 6 different definitions of evolution and step through them point by point.
Principal Meanings of Evolution in Biology Textbooks
1. Change over time; history of nature; any sequence of events in nature.
2. Changes in the frequencies of alleles in the gene pool of a population.
3. Limited common descent: the idea that particular groups of organisms have descended from a common ancestor.
4. The mechanisms responsible for the change required to produce limited descent with modification, chiefly natural selection acting on random variations or mutations.
5. Universal common descent: the idea that all organisms have descended from a single common ancestor.
6. “Blind watchmaker” thesis: the idea that all organisms have descended from common ancestors solely through an unguided, unintelligent, purposeless, material processes such as natural selection acting on random variations or mutations; that the mechanisms of natural selection, random variation and mutation, and perhaps other similarly naturalistic mechanisms, are completely sufficient to account for the appearance of design in living organisms.
If, by “evolution” we mean definition number 1, 2, 3, or 4, I think we can all conclude that evolution is fact, in that it has been demonstrated. The problem, however, is when materialists conflate the definitions and start to claim that numbers 5 and 6 have similarly been shown to be fact. Although there is some evidence that suggests 5 may be correct, it is far from proven fact. Worse than that, definition 6 veers out of the bounds of science and directly into metaphysical worldviews. I think it is important to keep these things in mind when debating with Darwinists, and to hold them to defining their terms properly.