There are three kinds of sentences and they are:

a)    The simple sentence
b)    The complex sentence
c)    The compound sentence

Study the following sentence.

He wrote a letter.

The sentence given above has only one clause. A sentence having only one clause is called a simple sentence.

More examples are given below.

The dog barked.
It rained.
She danced.
He worked.
She made coffee.
He worked in the garage.
He sat on the sofa.

You will have noticed that a simple sentence consists of just one finite verb.

Compound sentence

Consider the sentence given below:

He wrote a letter and she posted it.

The sentence given above consists of two clauses ‘He wrote a letter’ and ‘she posted it.’ Both of these clauses make complete sense and can stand independently. Both clauses are therefore main clauses. A sentence having two or more main clauses is called a compound sentence.

Note that the clauses in a compound sentence are connected by coordinating conjunctions such as and, or, but, yet, either…nor, both…and and neither…nor.

Examples are given below

He is slow but he is regular.

Here the main clauses ‘He is slow’ and ‘He is regular’ are connected by the coordinating conjunction but.

I went to the market and bought some vegetables.

Here the main clauses ‘I went to the market’ and ‘I bought some vegetables’ are connected by the coordinating conjunction and.

Complex sentence

Consider the sentence given below:

He wrote a letter while she watched TV.

This sentence consists of two clauses ‘He wrote a letter’ and ‘while she watched TV’. Here the clause ‘He wrote a letter’ makes complete sense and can stand independently. It is, therefore, a main clause. Now consider the clause ‘while she watched TV’. This clause, too, has a subject and a predicate of its own, but it doesn’t make complete sense. It is, therefore, a subordinate clause. A sentence having one main clause and one or more subordinating clauses is called a complex sentence.

More examples are given below:

She came because I asked her to come.
I don’t know what she means.
John spoke as though he were a born orator.
He said that the traitor should be put to death.