Is "断ったとは信じがたい" a nominalization?

Question

I'm not comfortable with how ~~とは... is used in my textbook:

彼{かれ}がひどいことをしたとは信{しん}じがたい。

That 信じる is only transitive makes me think that ~~とは... is a nominalization method. But, I've never seen that method of nominalization before. So, I interpret ~~とは... to be a conjunction and imply a direct object as such:

He did a really bad thing, and I just cannot believe it.

The straight-up nominalization interpretation (which I reject because of the nominalization method looks strange to me) would be:

I find it hard to believe that he did such an awful thing.

So, what's going on with the ~~とは... conjunction? / nominalization?

straight out of textbook

あの優しい彼がそんなひどいことをしたとは信じがたい。

note

断ったとは信じがたい

is used in the title because it is just shorter and should involve the same grammatical structure. If it's not, then learning the difference would be very instructive.

Answer 1

To break down, this とは is the quotative particle と, followed by the "topic marker" は. Probably you already know how to use と in sentences like these:

• 彼が学生だと聞いている。 I've heard he's a student.
• 明日は晴れると思う。 I think it will be fine tomorrow.
• プロジェクトが成功すると信じている。 I believe the project will succeed.

When you add は after と, such は will function as the marker of contrast. You probably know this, too.

• 彼が学生だとは聞いている。 I've heard he's a student (but nothing else about him).
• プロジェクトが成功するとは信じている。 (implies the speaker is expecting something bad can happen, despite the project's success)

These sentences are irrelevant to nominalization, although you can also rephrase some of these sentences using nominalizers (プロジェクトが成功することを信じている。).

Now, when these sentences are negated, these と are usually followed by は. This is discussed in another question.

Why is the topic marker often used in negative statements (ではない, ～とは思わない)?

• 彼が学生だとは聞いていない。 I haven't heard he's a student.
• 明日は晴れるとは思わない。 I don't think it will be fine tomorrow.
• プロジェクトが成功するとは信じていない。 I don't believe the project will succeed.

Unlike non-negative versions, there は are not necessarily contrastive, as discussed in the linked question. You just need them to make the sentences look natural. But these は after と are still optional, especially in relative clauses. And 信じがたい is semantically negative, although it's not grammatically negative.

(By the way, end-sentence とは can denote the speaker's surprise (eg 彼が学生だとは!), but I think mid-sentence とは are usually neutral)

Answer 2

「とは」 here is not being used for nominalization. As a matter of fact, I could not think of a situation where 「とは」 could be used for pure nominalization.

We are talking about 「とは」 and not 「ことは」, right?

「彼がひどいことをしたとは信じがたい。」 =

"I find it hard to believe that he did such an awful thing." to borrow your own TL.

In this sentence, 「とは」 expresses the speaker's surprise/disbelief/anger, etc. depending on the exact context.

This usage of 「とは」 is actually quite common.

「まさかヤンキースが[勝]{か}つとは！」 = "Never thought the Yankees would win!" Yes, you can end a sentence with this usage of 「とは」 without using a verb phrase.

「Aのような[小]{ちい}さな[町]{まち}に、こんなにうまいラーメン[屋]{や}があるとは[想像]{そうぞう}していなかった。」 = "I could not have imagined that there would be such a great ramen joint like this in a small town like A!"