In this essay, I argue that Wittgenstein attempted to clarify ethics through a procedure that, by analogy with “transcendental arguments”, I call “transcendental thought experiment”. Specifically, after offering a brief perspectival account of both transcendental arguments and transcendental thought experiments, I focus on a thought experiment proposed by Wittgenstein in his 1929 'Lecture on Ethics', arguing that it deserves the title of “transcendental”.