The distinction between philosophy and science (and math, engineering, etc.) is a very recent one (less than 200 years old). You may have heard the term "natura

The distinction between philosophy and science (and math, engineering, etc.) is a very recent one (less than 200 years old). You may have heard the term "natural philosophy" as an old term for science, but it betrays that fact that what we now call science was just another branch of philosophy. Remember that Descartes also authored major mathematical works. Philosophers of that day could and did do a little bit of everything. Anyway, his argument, and the other arguments of them time, were based on things like the fact that if the speed of light were finite, you would notice things like the sun, moon, and earth being out of alignment during an eclipse, since the earth's shadow would lag behind it. Since no such misalignment was observed, the speed of light must be infinite. Later philosophers pointed out, of course, that it was also possible that the speed of light was finite but very fast, and the eclipse lag time was immeasurably small. Then Roemer settled things once and for all.