The Structure of a Sentence


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Remember that every clause is, in a sense, a miniature sentence. Simple sentences contain only a single clause, while compound sentences, complex sentences and compound-complex sentences contain at least two clauses.

The simple sentence

The most basic type of sentence is the simple sentence, which contains only one clause. A simple sentence can be as short as one word:

  • Run!

Generally, however, the sentence has a subject as well as a predicate, and both the subject and the predicate may have modifiers. The following examples are simple sentences because each contains only one clause:

  • Melt!
  • Ice melts.
  • The ice melts quickly.
  • The ice on the river melts quickly under the warm March sun.
  • Lying exposed without its blanket of snow, the ice on the river melts quickly under the warm March sun.

As you can see, a simple sentence can be quite long—it is a mistake to think that you can tell a simple sentence from a compound sentence or a complex sentence simply by its length.

The most natural sentence structure is the simple sentence: it is the first kind that children learn to speak, and it remains by far the most common sentence in the spoken language of people of all ages. In written texts, simple sentences can be very effective for grabbing the reader’s attention or for summing up an argument, but you need to use them with care: too many simple sentences can make your writing seem puerile.

When you do use simple sentences, you should add transitional phrases to connect them to the surrounding sentences.

The compound sentence

A compound sentence consists of two or more independent clauses (or simple sentences) joined by a co-ordinating conjunction such as and, but and or:

Canada is a rich country.
It has many poor people.
Canada is a rich country, but it has many poor people.

Compound sentences are very natural for English speakers—small children learn to use them early on to connect their ideas and avoid pausing:

  • Today at school Mr. Moore brought in his pet rabbit, and he showed it to the class, and I got to pet it, and Kate held it, and we coloured pictures of it, and it ate part of my carrot at lunch, and . . .

This is an extreme example, but if you overuse compound sentences, your writing might seem childlike.

A compound sentence is most effective when you use it to create a sense of balance or contrast between two (or more) equally important pieces of information as follows:

  • Montréal has better clubs, but Toronto has better cinemas.

The complex sentence

A complex sentence contains one independent clause and at least one dependent clause. Unlike a compound sentence, a complex sentence contains clauses which are not equal. Consider the following examples:

My friend invited me to a party. I do not want to go.
My friend invited me to a party, but I do not want to go.
Although my friend invited me to a party, I do not want to go.

In the first example, there are two separate simple sentences: My friend invited me to a party and I do not want to go. The second example joins them together into a single sentence with the co-ordinating conjunction but. Note that both parts could still stand as independent sentences—they are entirely equal, and the reader cannot tell which is more important. In the third example, however, the sentence has changed quite a bit: the first clause, although my friend invited me to a party, has become incomplete, or a dependent clause.

A complex sentence is very different from a simple sentence or a compound sentence in that it makes clear which ideas are most important. For example,

  • My friend invited me to a party. I do not want to go.
  • My friend invited me to a party, but I do not want to go.

the reader will have trouble knowing which piece of information is most important. However, if the subordinating conjunction although appears at the beginning of the first clause, it is clear that the fact that your friend invited you is less important than (or subordinate to) the fact that you do not want to go.

Special types of compound sentences

There are two special types of compound sentences. The first type involves punctuation. It is possible to join two originally separate sentences into a compound sentence using a semicolon instead of a co-ordinating conjunction as follows:

  • The sun rises in the east; it sets in the west.

Generally, a conjunctive adverb such as however or consequently will appear near the beginning of the second sentence, although one is not required:

  • The package was delivered in the morning; however, the courier left before I could check the contents.

Rather than joining two simple sentences together, a co-ordinating conjunction sometimes joins two complex sentences, or one simple sentence and one complex sentence. This type of sentence is called a compound-complex sentence:

The package was delivered in the morning, but the courier left before I could check the contents.

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