What is the difference between ~ru and ~masu?


What is the difference between ~ru and ~masu? For example: taberu and
tabemasu. Don't they mean the same thing? Are there certain instances when one
is acceptable and the other isn't?




A couple of things the other answers didn't address:

  1. The ～る form is also referred to as the "dictionary form" ([辞書形]{じ・しょ・けい}). This is how you look up verbs in the dictionary. So if you need to look up "to eat" in a Japanese dictionary, you search for [食]{た}べる, not [食]{た}べます. Likewise, if you see the verb [会]{あ}う in the dictionary, you know this is the correct entry corresponding to the verb [会]{あ}います.

  2. The ～ます form is usually referred to as "Polite form/speech" ([丁寧語]{てい・ねい・ご}). It is sometimes used in formal situations, but not necessarily. It's one thing to speak politely; it's another to speak formally. @BrandonAzer's examples at the top are not quite correct. It is more like:

>   * ケーキを **食べる** → Informal/Familiar
>   * ケーキを **食べます** → Polite, neutral
>   * ケーキを **いただきます** → Formal, humble
>

Formal speech/situations are most often accompanied by special _words_ called
[敬語]{けい・ご}, not different _forms_ of informal words.

