English grammar - Roger Berry 2012
B9.3 Exclamatives
B9 Clause types
Section B Development
Exclamatives are said to be sentences expressing a strong emotion: exclamations, in other words. In writing they are usually signalled by an exclamation mark.
What a nice day it is!
How quickly they reacted!
They may start with either what or how; in both cases a clause element is fronted (see A11). In the first example a noun phrase containing what (a predicative in this case) has been fronted (It is such a nice day), and in the second an adverb phrase (functioning as an adverbial) (They reacted very quickly).
Exclamatives are rarer than the other clause types, and a negative is not possible: ’What a nice day it isn’t!’ They are also found in minor sentences: What a fool!