It’s common to see exclamative sentences like these:
What a beautiful sunset this is!
How incredible that performance was!
The above exclamatives are independent clause, but they can be dependent as well. (Well, they can be phrases as well.)
An exclamative (or exclamatory) clause is a dependent clause expressing strong emotions and opinions. Like their independent counterpart, they’re introduced by what or how. They function like a noun clause, occupying nominal positions of subject, direct object of verb, and object of preposition. Exclamative clauses as subject are usually extraposed. (If you extrapose a subject, you move it to the end of the main clause and replace it by dummy subject it.) Examples:
It is astonishing what an impact she has on everyone she meets. [Extraposed subject]
It is shocking how slow the progress is. [Extraposed subject]
She couldn’t believe what a fantastic job they had done. [Direct object of verb]
You wouldn’t believe how much she has improved. [Direct object of verb]
They were in awe of what a stunning performance he delivered. [Object of preposition]
I was amazed at how quickly she learned. [Object of preposition]
Note that unlike exclamative sentences, exclamative clauses don’t end with an exclamation sign (!). That’s because they’re embedded in sentences and can’t have punctuation of their own.
If an exclamative clause functions like a noun clause and if it has generally the same word order as a noun clause, aren’t two the same? They aren’t. They differ in few ways:
1. Exclamative clauses can only be introduced by what and how. Whereas what is a predeterminer (it is always followed by central determiners a or an.), how is an intensifying adverb.
Noun clauses are introduced by a variety of introductory words, including what and how. Here, what is an interrogative pronoun or (central) determiner, and how is an interrogative adverb or (central) determiner.
2. As mentioned earlier, exclamative clause can occupy only three nominal positions: subject, direct object of verb, and object of preposition. Noun clauses can occupy most nominal positions in a sentence.
