In the chapter Things that should be a certain way of Tae Kim's guide, the author states that in order to express the expectation of something not happening, one should use something like 「～はずがない」. I was wondering if the Japanese language distinguishes phrases like "I don't expect him to come" vs. "I expect him not to come"? In other words, are both of these acceptable:
If not, are there other constructs to express this?
Both are acceptable.
But note that each of them has a different meaning. And these meanings are subtly different.
彼は来ないはずです。
= We have the expectation that he won't come.
彼は来るはずがない。
= We do not have an expectation that he is coming.
The difference here is that we are stating our expectation in the first case. In the second, we are negating an expectation. In the first the expectation is negative. In the second, the expectation is positive. Turned into a chart:
～ないはず ～はずがない ～ないはずではない
Expectation - + -
Statement + - -
Net Statement - - +
来るはずがない is understood to be stronger than 来ないはずです in terms of the strength of our belief he wont' come by native speakers.
彼は来るわけがない。
= We have no reason to expect he will come.
But
どうりで彼は来ないわけです
= It's no wonder he doesn't come
I am going to offer a simpler explanation making reference to the previous answers and comments (avoiding any consideration of changing は or が ) :
Both are acceptable, both indicate the actor is not expected to visit but there is a difference which can be shown by the following which are quite close to the normal translation of はず into standard English:
彼は来ないはずです。| I expect he won't come.
彼は来るはずがない。| I have no expectation of him coming [at all].
As explained by 明鏡国語辞典 (in Snailplane's comment), the second case is much stronger because the speaker is excluding any possiblity of the actor coming. (皆無＝＞"There is no chance he is coming.")
わけ＜＝＞はず
This was not part of the question but it is a worthwhile comparison:
はずがない and わけがない are taught as interchangeable. I rationalise this on the basis that わけ is used to convey circumstances or a reason, as follows:
彼は来るわけがない。
He has no reason to come.
or
He is not coming under any circumstances.
(~There are no circumstances under which he will come.)
=> I have no expectation of him coming [at all].
The expression 「彼は来ないわけです。」, on the other hand, might be used to explain: "That is because he is not coming.", or depending on the situation: "Yes but he is not coming."
I think those two sentences are equally acceptable. As for the other way, 彼が来るはずはない. In 彼は来るはずがない, "he" is the point of attention, and this expression implies other persons except him will come, like 彼女は来るはず. In 彼は来ないはずだ, "won't come" is the point of attention, and this implies he will do other actions, like 彼は他の場所へ行くだろう. In 彼が来るはずはない, "彼がくるはず" is a noun clause.
