Expressing yourself clearly in writing is easier if you know how various sentence types are constructed. At its most basic, this means understanding the differences between simple, complex and compound sentences.
A simple sentence includes just one independent clause and expresses a complete thought. Minimally, this means having a subject and a verb (i.e. an action word), such as in:
Other verbs require an object (these are known as transitive verbs). A sentence with an object can still be simple, though, since it remains a single independent clause:
Not all ‘simple’ sentences are quite this simple, since we can add extra information to a sentence without changing the basic structure. Take the following, for example:
He and I both play the violin badly.
Here, we have a compound subject (‘He and I’), a determiner (‘both’), a verb (‘play’), a direct object (‘the violin’) and an adverb (‘badly’). Nevertheless, it’s still a simple sentence.
If we have more than one independent clause in a sentence, it becomes a compound sentence. Usually, this will involve joining the two clauses with a coordinating conjunction:
‘And’ is possibly the most common coordinating conjunction, but you can use the acronym FANBOYS to help you remember the complete set (i.e. For, And, Nor, But, Or, Yet, So).
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The important thing is that the statements on either side of the conjunction in a compound sentence could work as sentences by themselves. It’s also worth keeping in mind that you should use a comma before the conjunction when linking two independent clauses.
A complex sentence combines an independent clause with at least one dependent clause (i.e. a clause that contains a subject and a verb, but which doesn’t express a complete thought).
To join an independent and a dependent clause, we typically use a subordinate conjunction (‘because’, ‘until’, ‘unless’, ‘while’, etc.) to show how the two clauses are related:
He will never master the violin unless he starts practising.
Here, the main clause (‘He will never master the violin’) is linked to the dependent clause using the subordinate conjunction ‘unless’. The crucial thing is that the second part of the sentence wouldn’t make sense by itself, so it depends on the main clause to express something.
We can also begin a sentence with a dependent clause. If we do this, the two clauses should be separated with a comma:
Unless he starts practising, he will never master the violin.
Another way of making a complex sentence involves adding a relative clause using a relative pronoun (e.g. ‘who’ or ‘which’). This would look like the following:
He plays the violin badly, which gives me a headache.
As with other dependent clauses, relative clauses only make sense when joined to an independent clause.
Finally, when a sentence contains at least two independent clauses and at least one dependent clause, we refer to it as a compound-complex sentence. For example:
He plays the violin that I bought him, but he does it badly.
Here, we have an independent clause (‘He plays the violin’), a dependent clause (‘that I bought him’) and a second independent clause after a coordinating conjunction (‘but he does it badly’). This lets us express more complicated ideas in a single sentence.
Varying Sentence Type
A well written document will usually contain all of these sentence types. As such, varying your sentences is a good idea.
Using too many short, simple sentences, for example, can mean your writing doesn’t flow. In this case, using more compound and complex sentences could help.
If you use too many long and complicated sentences, though, your writing could be difficult to follow. As such, breaking them down into shorter, simpler sentences might improve readability.