There are three main sentence types, described below: simple, compound, and complex.
2.2.1 Simple Sentences
A simple sentence consists of a single independent clause, as in:
The doorman greeted me.
The company hired thirty new employees last quarter.
2.2.2 Compound Sentences
A compound sentence consists of two or more independent clauses. The clauses can be combined in various ways.
In the following sentence, for example, the coordinating conjunction and combines two independent clauses.
The seminar starts at 9:00, and lunch should arrive by noon.
Although subordinating conjunctions are part of their dependent clauses, the and above does not count as part of either independent clause.
In the next example, a semicolon combines two independent clauses to form another type of compound sentence.
The company hired thirty new employees last quarter; it also opened a new factory.
A third example of a compound sentence, below, contains three independent clauses, each indicated with brackets. The coordinating conjunction but combines the first two, and the coordinating conjunction so combines the second and third.
[Aaron originally disapproved of the plan to expand the cafeteria], but [his co-workers all supported it], so [he decided to vote in favor of the idea].
A run-on sentence is a major grammatical error occurring when a writer joins independent clauses with nothing but air, as in:
The proposal is on its way you should have it by noon.
Avoid run-ons, even in the quickest and most casual of emails.
2.2.3 Complex Sentences
A complex sentence consists of at least one independent clause combined with at least one dependent clause. The following examples illustrate various structural possibilities:
Dependent Clause + Independent Clause
If it snows, the company will cancel the outing.
Independent Clause + Dependent Clause
The company will cancel the outing if it snows.
Dependent Clause + Two Independent Clauses
Because Roger had to pick up his children from school, he submitted his article early; unfortunately, he didn’t have much time to proofread it.