A compound sentence contains two or more independent clauses connected by a coordinating conjunction. You can find out the number of independent clauses in a sentence by counting the number of coordinating conjunctions in it. If a sentence has two independent clauses, it will usually have one coordinating conjunction. If it has three independent clauses, it will usually have two conjunctions. Remember that in English, we use just one conjunction to join two clauses.
The most important coordinating conjunctions in English are: and, but, or, for, nor, so and yet.
A complex sentence contains one independent clause and one or more dependent (subordinate) clauses. You won’t find the coordinating conjunctions in a complex sentence, but you will see one or more subordinating conjunctions. Common subordinating conjunctions are: because, as, since, while, when, before, after, that, so…that, if, whether, unless etc.
If a compound sentence contains just two independent clauses, you can convert it into a complex sentence by changing one of these independent clauses into a dependent clause. If the compound sentence contains three independent clauses, you will have to change two of them into dependent clauses.
Study the example sentences given below.
- Compound: Take care of the pence, and the pounds will take care of themselves.
As you can see, this sentence contains two independent clauses connected by the coordinating conjunction and.
If you look closer, you can see that this sentence implies a condition. We can express the same idea using the subordinating conjunction if.
- Complex: If you take care of the pence, the pounds will take care of themselves.
Another example is given below.
- Compound: Speak the truth, or I will kill you.
This sentence contains two coordinate (independent) clauses connected by the conjunction or.
We can change this into a complex sentence by converting one of these clauses into a dependent clause.
- Complex: I will kill you if you don’t speak the truth.
