Using the semi-colon and colon

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Sentence structure

Study guide

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This guide explains how sentences are constructed and how different types of sentences are formed. It shows you how to punctuate each type correctly and how to combine different sentence types for effective written communication.

Other useful guides: Using paragraphs, Using the comma.

What is a complete sentence?

Sentences provide us with the framework for the clear written expression of our ideas. The aim in writing is always to write in complete sentences which are correctly punctuated. Sentences always begin with a capital letter and end in either a full stop, exclamation or question mark. A complete sentence always contains a verb, expresses a complete idea and makes sense standing alone.

Andy reads quickly. This is a complete sentence as it contains a verb (reads), expresses a complete idea and it does not need any further information for the reader to understand the sentence.

When Andy reads is an incomplete sentence. It contains a verb, but the opening word when tells us that something happens when Andy reads; we need more information to complete the idea.

When Andy reads, he reads quickly. This is now a complete sentence, as the whole idea of the sentence has been expressed. The following examples show the incomplete sentences in italics.

There is another theory. Which should not be ignored.

There is another theory which should not be ignored.

 

The proposal was finally rejected. Although they considered it.

Although they considered the proposal, it was finally rejected.

To check that you are writing in complete sentences, try reading your sentences aloud, pausing as indicated by the punctuation. Can each sentence stand alone as a complete thought? If further information is needed to complete the idea, then it is not a complete sentence.

Types of sentences

As well as being able to write in complete sentences, it is important to be able to use a variety of sentence types that are correctly punctuated.

Sentences are made up of clauses: groups of words that express a single idea. There are two types of clauses: independent clauses and dependent clauses. Independent clauses can stand alone as complete sentences. A dependent clause needs an independent clause to complete its meaning. Different types of sentences are made up of different combinations of these two types of clauses.

Simple sentences consists of just one independent clause; it requires only one punctuation mark at the end (a full stop, exclamation or question mark).

The essay was late.

Compound sentences are made by joining simple sentences. We join sentences which are closely related in content to make the writing more fluid. We can join simple sentences with a comma and a word such as: and, but, so, yet.

The essay was late, so he lost marks.

We can also join simple sentences with a semi-colon.

The essay was late; he lost marks.

Complex sentences are made when we combine an independent clause with a dependent clause. The dependent clause in the following example is in italics.

Because his essay was late, he lost marks.

When the dependent clause comes first, as in the example above, it is separated from the independent clause with a comma. When the sentence begins with the independent clause, there is no need to separate the clauses with a comma.

He lost marks because the essay was late.

Comparing these two examples,it can be seen that the emphasis tends to fall on the clause at the beginning of the sentence. Vary your placement of dependent clauses in order to emphasise the most important idea in the sentence. Common ways to begin a dependent clause are: although, as, because, even though, if, instead, through, when, whenever, where, while.

Whilst more than one dependent clause can be used in a sentence, they must always be combined with an independent clause to complete the idea. Again, the dependent clauses in this example are in italics.

Although there are many dissenters, many of whom were prominent citizens, the policy still stands today.

Different types of sentences can be combined to form compound-complex sentences. In the example below, the central independent clause combines two sentence types. It serves as both the ending of the complex sentence and the beginning of the compound sentence.

When considering owning a pet, you must calculate the cost, or the animal may suffer.

When punctuating a compound-complex sentence, apply the rules for both compound and complex sentences. The example above begins with a dependent clause separated from the central clause by a comma, as in the rule for complex sentences. At the end of the sentence the independent clause is joined by a comma and the word or, as in the rule for the compound sentences.