Question: I was studing how to say school subjects in mandarin and I saw this sentence:

我最喜欢的科目**有**艺术，中文和化学
(My favorite school subjects are art, chinese and chemistry)

Why the use of 有 in this sentecence?

Could I say/write: 我最喜欢的科目是**是**艺术，中文和体育

Answer: 
有 (have) = include

是 (is/ are) = exclusively

我最喜欢的科目有艺术，中文和化学 - doesn't exclude the possibility of there are other subjects I like

我最喜欢的科目是艺术，中文和体育 - specifically stated these three subjects are the ones I like
I have some issues with the first sentence, though it is not wrong. I would say:

我最喜欢的科目有三個 - 艺术，中文和化学 (There are three of my most favored school subjects - ... or

我最喜欢的科目包括 艺术，中文和化学 (My most favored school subjects include ....

The second sentence is perfectly correct.