The other classifications in this chapter describe how you construct your sentences, but this last set describes why you have written the sentences in the first place. Most sentences which you write should simply state facts, conjectures, or arguments, but sometimes you will want to give commands or ask questions.
The Declarative Sentence
The declarative sentence is the most important type. You can, and often will write entire essays or reports using only declarative sentences, and you should always use them far more often than any other type. A declarative sentence simply states a fact or argument, without requiring either an answer or action from the reader. You punctuate your declarative sentences with a simple period:
Ottawa is the capital of Canada.
The distinction between deconstruction and post-modernism eludes me.
He asked which path leads back to the lodge.
Note that the last example contains an indirect question, "which path leads back to the lodge." An indirect question does not make a sentence into an interrogative sentence -- only a direct question can do that.
The Interrogative Sentence
An interrogative sentence asks a direct question and always ends in a question mark:
Who can read this and not be moved?
How many roads must a man walk down?
Does money grow on trees?
Note that an indirect question does not make a sentence interrogative:
When was Lester Pearson prime minister?
I wonder when Lester Pearson was prime minister.
A direct question requires an answer from the reader, while an indirect question does not.
The Rhetorical Question
Normally, an essay or report will not contain many regular direct questions, since you are writing it to present information or to make an argument. There is, however, a special type of direct question called a rhetorical question -- that is, a question which you do not actually expect the reader to answer:
Why did the War of 1812 take place? Some scholars argue that it was simply a land-grab by the Americans ...
If you do not overuse them, rhetorical questions can be a very effective way to introduce new topics or problems in the course of a paper; if you use them too often, however, you may sound patronising and/or too much like a professor giving a mediocre lecture.
The Exclamatory Sentence
An exclamatory sentence, or exclamation, is simply a more forceful version of a declarative sentence, marked at the end with an exclamation mark:
The butler did it!
How beautiful this river is!
Some towns in Upper Canada lost up to a third of their population during the cholera epidemics of the early nineteenth century!
Exclamatory sentences are common in speech and (sometimes) in fiction, but over the last 200 years they have almost entirely disappeared from academic writing. You will (or should) probably never use one in any sort of academic writing, except where you are quoting something else directly. Note that an exclamation mark can also appear at the end of an imperative sentence.
The Imperative Sentence
An imperative sentence gives a direct command to someone -- this type of sentence can end either with a period or with an exclamation mark, depending on how forceful the command is:
Read this book for tomorrow.
You should not usually use an exclamation mark with the word "please":
Wash the windows!
Please wash the windows.
Normally, you should not use imperative sentences in academic writing. When you do use an imperative sentence, it should usually contain only a mild command, and thus, end with a period:
Consider the Incas.