Translation of negative hypothetical + naranai

[richvh]

My penpal sent me a message including this line: 「今日はhospitalに行かなければならない。」 I was able to figure out that "ikanakereba" was the negative hypothetical of "iku", and she explained that "naranai" meant "ought to" or "should", but I'm having a problem figuring out what they mean together.

Edit: Never mind, I found it in Tae Kim's Guide. "Ikanakereba naranai" = "Have to go".

[InsanityRanch]

That is the usual way of saying must do something in Japanese. It translates to, I can't NOT do it.

[Harisenbon]

InsanityRanch is right on the money. However, in more simple english, it translates into "I have to"
So your friend has to go to the hospital.

[roomwithamoose]

Yes, this is all correct, if you are interesting in a more detailed explanation here you go:

naranai = negative informal form of naru(to become)

When one combines this with nakereba, it literally means, "if one does not..., won't become." Simply put, this means "if it doesn't happen it won't do." In English we use the word "must" or "have to" to express this. As you may have noticed, one may make it more polite by changing naranai to narimasen. Also, because this is an oftely long conjegation, a very informal thing one may do is replace "~nakereba naranai" with "~nakya". However, I do not live in Japan so I'm unsure how often this is used, this is just from what I've read.