Dot Physics: Some things about science

Aristotle and the other Greeks: They started with assumed truths like heavy things fall faster than lighter things. From that they deduced ideas about motion. The problem here is that if your “assumed truths” are wrong, you are in big trouble. They did not actually test their assumed truths. If they did, they wouldn’t be assumed.

This is a common bugbear of the crackpot, too, who starts with some flawed assumption about how nature behaves and ends up concluding that his perpetual motion machine will work.