We can all speak and understand each other; do we need to investigate how?

3.6 Imperative sentences

Imperative sentences express commands which convey the desire of the speaker to make someone, generally the listener, perform an action. Besides commands proper, imperative sentences may express prohibition, a request, an invitation, a warning, persuasion, etc., depending on the situation, context, wording, or intonation.

Stand up! Sit down. Open your textbooks.

Be quick!

Formally commands are marked by the predicate verb in the imperative mood (positive or negative), the reference to the second person, lack of subject, and the use of the auxiliary do in negative or emphatic sentences with the verb to be.

Commands are generally characterized by the falling tone, although the rising tone may be used to make a command less abrupt. In writing commands are marked by a full stop or an exclamation mark.
A negative command usually expresses prohibition, warning or persuasion.

Don’t cross the street before the light turns to green.

3.7 Exclamatory sentences

The main distinctive feature of this communicative type of sentence is a specific intonation; structurally it is variable.

You do look a picture of health! (statement)

Hurry up! (command)

The most common pattern of an exclamatory sentence opens with one of the pronominal words what and how. What refers to a noun, how to an adjective or an adverb. An exclamatory sentence has a subject-predicate structure; the order of the subject and the predicate verb (or the operator) is not inverted. An exclamation has a falling tone in speaking and an exclamation mark in writing.

What a funny story she told us!
What valuable advice you’ve given us!

Besides these patterns an exclamation as a communicative sentence type often follows the pattern of other sentence types. Thus it may be formed on the pattern of the following structures:

1. Statements:

You do look a picture of health!

2. Commands:

Hurry up!

3. Questions. These are “yes-no” questions functioning as exclamations owing to the falling tone in speaking and an exclamation mark in writing. The most common pattern has a negative question form with the operator heavily stressed.

Isn’t it funny! (How funny it is!)
Wasn’t it a funny story! (What a funny story it was!)