SENTENCE TYPE AND PURPOSE
Sentences come in a variety of shapes and lengths. Yet whatever their shapes and lengths (or types), all sentences serve one of only a few very basic purposes.
Sentence variety is not about mere novelty; it is about meaning. You can avoid boredom (yours and your readers') and choppiness by varying your sentence types. Longer, more complex sentences can increase the impact of a shorter, simpler sentence.
Every sentence is one of the following types.
In order to vary your writing, you want to be able to construct sentences of each kind. To master these four types, though, you really only need to master two things: independent and dependent clauses. This is because the four types of sentences are really only four different ways to combine independent and dependent clauses.
(Let's review: independent clauses are essentially simple, complete sentences. They can stand alone or be combined with other independent clauses. Dependent clauses are unfinished thoughts that cannot stand alone; they are a type of sentence fragment and must be joined to independent clauses. For more information, see the TIP Sheet Independent & Dependent Clauses: Coordination and Subordination.)
The simple sentence
A simple sentence is simple because it contains only one independent clause:
Justin dropped his Agricultural Economics class.
A simple sentence is not necessarily short or simple. It can be long and involved, with many parts and compound elements. But if there is only one independent clause, it is, nevertheless, a simple sentence. The following example has a single independent clause with a single subject (Justin) and a compound verb (gulped, swallowed, groaned, and decided):
Justin gulped down his fourth cup of coffee, swallowed a Tylenol for his pounding headache, groaned, and decided he would have to drop his Agricultural Economics class.
The compound sentence
When you join two simple sentences properly, you get a compound sentence. Conversely, a compound sentence can be broken into two complete sentences, each with its own subject and its own verb. You can join simple sentences to create compound sentences either of two ways:
For example, the following pairs of independent clauses can be joined either way:
Homer has Basic Plant Science on Mondays and Wednesdays; Environmental Horticulture conflicted with his schedule.
Homer has Basic Plant Science on Mondays and Wednesdays, but Environmental Horticulture conflicted with his schedule.
(Be aware that if you join two simple sentences improperly, you do not get a compound sentence; you get a run-on, most likely either a comma splice or a fused sentence. For more information, see the TIP Sheets Comma Splices and Run-on Sentences and Independent & Dependent Clauses: Coordination & Subordination.)
The complex sentence
A complex sentence is a sentence that contains both a dependent and an independent clause. In the following example, both clauses contain a subject and a verb, but the dependent clause has, in addition, the dependent-making words even though. If you start the sentence with the dependent-making words (or subordinating conjunction), place a comma between the clauses. On the other hand, if you start with the independent clause and place the dependent-making words in the middle of the sentence, do not use a comma:
Even though Eva took Turf Management just to fill out her schedule, she found it unexpectedly interesting.
Eva found Turf Management unexpectedly interesting even though she took it just to fill out her schedule.
(For more on subordinating conjunctions, see the TIP Sheet Independent & Dependent Clauses: Coordination & Subordination.)
The compound-complex sentence
A compound-complex sentence combines at least two independent clauses and at least one dependent clause. The punctuation rules remain the same: the two simple sentences are joined by one of the two methods described above, and the dependent clause is punctuated (or not) depending on whether it precedes or follows an independent clause. In the following example, the dependent-making word signaling the beginning of the dependent clause is while:
Homer was already in class, and Eva was in the lab while Justin was sleeping off his headache.
While Justin was sleeping off his headache, Homer was already in class, and Eva was in the lab.
Homer was already in class while Justin slept off his headache; Eva was in the lab.
Sentences can do different things. The purpose of some sentences is to make statements. Declarative sentences make statements and end with periods:
I am planning to drop Agricultural Economics.
The purpose of another sentence may be to pose a question. These interrogative sentences ask questions and end with question marks:
Have you taken any Agricultural Engineering classes?
Imperative sentences give commands or make demands or requests. They usually end with a period. An imperative sentence often has as its subject an unstated "you" (giving to beginners in English grammar the appearance of lacking a subject altogether). The subject of each of the following four sentences is "you:"
Hand in your homework assignments, please.
Stop. Drop. Roll.
Exclamatory sentences convey strong emotion and end with exclamation marks; use them sparingly:
Watch out for the rattlesnake!