47601
What is the difference between

> 勉強が終わったとたん、眠くなった。

and

> 勉強をしたとたん、眠くなった。
CC BY-SA 3.0
2017-05-19T16:01:58.193
47585
2017-05-20T04:27:47.727
19672
question
grammar word-choice
Usage of ～とたん and nuances
> 勉強が終わったとたん、眠くなった。

This pretty straightforwardly means "The moment I finished studying, I became
sleepy."

> 勉強をしたとたん、眠くなった。

とたん is "the moment ～", and 勉強 is an action that takes some time (typically
more than an hour). I wouldn't say this sentence is wrong, but I feel this one
is a bit clumsy and ambiguous. Anyway it's probably taken as "The moment I
_started_ studying, I became sleepy."
CC BY-SA 3.0
2017-05-19T23:31:19.647
47596
2017-05-19T23:31:19.647
5010
47585
answer
> What is the difference between  
>  1. 勉強が **終わった** とたん、眠くなった。  
>  and  
>  2. 勉強をしたとたん、眠くなった 。

If you want to know if the sentence 2 has a similar meaning of 1 and if it is
made from the sentence 1 by omitting the phrase 終わった and adjusting the
sentence a little, **the answer is yes and no**.

**とたん** means like " _the moment_ ...", " _just at the moment_ ", and " _just
as_ ...", so the phrase is in good relations with " **moment** ".

If you know this, the sentence 2 could be interpreted in two ways;  
one of which is the sentence 1 and the other is the sentence 3 as follows:

>   3. 勉強を始｛はじ｝めたとたん、眠くなった。
>

If so, the sentence is **ambiguous** because it has quite different meanings.

Of course I know 勉強した often means 勉強し終わった, like 食べた means 食べ終わった. But,
grammatically 勉強した is the past form of 勉強する, and 勉強する is not necessarily meant
to finish studying or finish learning, but it also means the whole act of
studying or learning **for a certain span of time**. And the span of time has
not good relations with "moment" as is written in naruto's answer.

With these reasons, although the sentence 2 has the same meaning of 1 to some
extent, I don't recommend you to use it as the sentence 1.
CC BY-SA 3.0
2017-05-20T02:29:47.560
47601
2017-05-20T04:27:47.727
2017-05-20T04:27:47.727
20624
20624
47585
answer