Wittgenstein believed that he had resolved many areas of philosophy, such as Ethics, Morality, Aesthetics, and especially Metaphysics by showing that what philosophers were discussing when attempting to work on these problems were merely problems of language (i.e., arguing about semantics). While he thought many of these areas were areas were extremely important to human life, nothing sensible (quite literally, nothing which related to the senses) could be spoken about them. Instead of doing metaphysical speculation, he thought philosophers could only work clarifying the concepts we use in language. The only job a philosopher could have in metaphysics, Wittgenstein thought, was to stand in the corner of a philosophy class and smack down the teacher when they said something beyond the scope of what could sensibly be said (like, for example, pretty much anything metaphysical).

"Oh and I almost forgot, one more demand: we need eight billions dollars to construct an imaginary Large Hadron Collider to help us with our thought experiments."

Ironically, it is the best of all possible worlds where most people think The Monadology is stupid.

Parmenides believed that reality was unified, eternal, and unchanging. He thought any change we see is only an illusion. His pupil, Zeno, went on to come up with many famous thought experiments, showing the inherent contradictions in believing that the Universe is divisible into parts, or that change or motion occurs.
Leibniz believed that God would create the Universe in the most perfect possible way, because God is perfectly rational, and perfectly good, He would only select the best possible Universe to be the one that was actually created. I know that seems unlikely, on account of how this world is total garbage, but the other possible worlds probably don't even have amazing huge wigs, or something like that.

"Also, buy my new book 'How to be Totally Stoic in 21 Easy Steps'"
"What the hell, all the pages are blank, I want my money back!"
"Ah, you can't change the book though, you can only change your reaction to the book. Also, no refunds."

And so Hume's skepticism was defeated. Or...was it? Can we really ever know? Dun dun dunnnnnn.

See the notes on The Fresh Prince of Philosophy, where Kant defeated Hume's skepticism with his sweet rhymes.

"A communist society will be organzied by the principle: from each according to his ability, to each according to his need"
"Marx, chain smoking is NOT an ability"
"Oh yeah? Then I'd like to see you try it"