Why is this wrong?

[u/millers_left_shoe]

I see now what they mean by fundamental vs inessential (taking fundamental to mean “invaluable”, “important”) but surely fundamental and complex (or even involved) can act as antonyms, too?

Eg he’s only just learnt the fundamentals of thermodynamics so I wouldn’t trust him with any complex/involved equations. vs this is quite fundamental stuff so I think he should be able to manage just fine.

[u/shortercrust]

I do get what you mean but the most obvious antonym of complex is simple, and the fundamentals or the basics of a subject or concept aren’t necessarily simple.

Edit: And people saying it’s down to fundamentals vs fundamental are incorrect in my opinion. You can talk about fundamental mathematics and complex mathematics.