It requires assumptions:
Sometimes you will hear that “science requires faith,” for example faith that our sense data are reliable or that nature really obeys laws. That’s an abuse of language; science requires assumptions, just like anything else, but those assumptions are subject to testing and updating if necessary. If we built theories on the basis of our sense data, and those theories kept making predictions that turned out to be wrong, we would examine and possibly discard that assumption. If the universe exhibited a chaotic jumble of non-lawlike behavior, rather than falling into beautiful patterns, we would abandon that assumption as well. That’s the most compelling thing about science: it always stands ready to improve by casting out an old idea when the evidence demands it.
~Sean Carroll, via The A-Unicornist.