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
You should know that the Chinese word 有 sometimes correspond to **there be** in English, so the case you mentioned could also be interpreted as a **there be** sentence. Take an example:

院子里**有**一棵树。  

There is a tree in the yard.

我最喜欢的科目**有**艺术、中文和化学。  

There are art, chinese, and chemistry, in (the list of) my favorite subjects.

While the Chinese word 是 sometimes correspond to **be** in English.

我最喜欢的科目是艺术、中文和化学。  

My favorite subjects are art, chinese, and chemistry.