Difference between はじめる and ようになる

Question

Compare the following sentences:

日本語を勉強しはじめた。
日本語を勉強するようになった。

I normally think of ようになる as expressing a gradual change. So maybe I studied just a little bit two years ago, a bit more last year, and this year I'm studying hard. I suspect that this is not what 勉強するようになった actually means though. Can ようになる describe a sudden change of state, i.e. today I decided that from now on I will study Japanese?

What about はじめる? It was suggested to me in a comment to one of my answers that はじめる is "to start doing something at the moment and implies that the action will not be continuing for a long time". I always used to think that はじめる simply meant "to start" with no restrictions on time etc. Now I'm not so sure.

In short, when should I use はじめる and when should I use ようになる to describe starting something.

Answer 1

Can ようになる describe a sudden change of state, i.e. today I decided that from now on I will study Japanese?

It can't unless you actually work on it. However...

Can ようになる describe a sudden change of state?

Yes, once the sudden change is carried out, you can use it.

I always used to think that はじめる simply meant "to start" with no restrictions on time etc.

How you understand it is correct. In other words, はじめる doesn't necessarily mean it's a habit, which ようになる implies. So, 勉強しはじめる just generally means to start studying, while 勉強するようになる means that how one studies becomes a habit.

日本語を勉強してはじめた

It means that you started something after you studied Japanese.