What's the difference between 也 (ye3) vs. 又 (you4)?
This last link contrasts 又 with 再 (zai4).
Both 也 and 又 can mean "also" . (也 is more literary, 又 is more colloquial)
(既~也~) is a common structure that connect two verb or adjective phrases
"他既教油畫, 也教中國畫" (beside teaching oil painting, he also teaches Chinese painting)
(又~又~) and (既~又~) are common structures that connect two verb or adjective phrases
"他又教油畫, 又教中國畫" (first 又 can be omitted )
"既殺人又放火" - beside killing people, he also burning down villages (既 can be omitted )
However both 也 and 又 have other meanings that are not interchangeable. Most noticeably 又 can mean "again" , while 也 cannot; 也 can mean "still/ even" while 又 cannot.
also; besides; either; too
and; also; again; in addition to
也 means "too", "also": 我也是. Me too.
又 means "again": 今天又下雨了. It rained again today.
In informal speech, 也 is more neutral. It simply conveys the information that something is the same as something else. 他也是一个学生。He is also a student.
又 can have a negative connotation. 他又这样! He is doing it again!