Galileo's Thought Experiment on the Moon

Philosophers are often accused of engaging in armchair speculation, as far removed from reality as possible. The quintessential example of this practice is the thought experiment, which many scientists sneer at precisely because it doesn’t require one to get one’s hands dirty. And yet scientists have often engaged in thought experiments, some of which have marked major advances in our understanding of the world. Just consider the famous example of Galileo’s thought experiment demonstrating (rather counter intuitively) that two objects of different weight must fall at the same speed. And, perhaps more famously, Einstein's light thought experiments, which lead him to the formulation of the theory of relativity.

And then, there are the other kind, like philosopher David Chalmers' famous thought experiment about zombies and the so-called "hard problem" of consciousness. Chalmers comes up with an (admittedly ingenious) little story, and we are supposed to deduce from it the momentous conclusion that there is more than matter/energy to the universe? Still, there are plenty of good thought experiments in philosophy, beginning with the so-called trolley dilemmas meant to probe our moral intuitions.