/lit/ - Literature

I've read through a lot of Plato's dialogues and am now reading Aristotle's Metaphysics. I feel like I'm gaining a solid grasp of them both but they seem to presuppose a non-materialist metaphysic, which is a big step to a modern reader.

I'm struggling to actually understand why forms/essences/substances must necessarily exist? I grew up in a very atheistic/materialistic/sciencebro household (brother is a physicist), so when I look around the world, I just see physical stuff - I don't see stuffness, if that makes sense.

For example, when I look at my coffee mug, I just see porcelain arranged in a particular way so that it can be used for the purpose of drinking. What is the philosophical proof the existence of an essence of a mug - mugness - or the form of a mug, whether that be in the Platonic ideal sense or the hylomorphic sense?

Maybe a mug is a bad example but the same with a tree. What is the philosophical proof for the existence of a tree-substance?

Any paper recommendations would be appreciated too.

I am...
evolving...

This is torture.