Many experts try to make definition about sentence. They express slightly different opinion about definition of sentence, but in general they have something in common. Oshima and Hogue (1991: 77) state that a sentence is a group of words that consists of at least one subject and one predicate and can stand by itself. While, Hornby (1974: 64) says that a sentence is the largest grammatical unit, consisting of phrases or clauses used to express a statement, question, and command. Then, Bolinger (1975: 32) defines a sentence as the minimum part of the language that expresses a complete thought. Similarly, Alexander (1988: 45) says that a sentence is a complete unit of meaning, both in spoken and written form. And, Lester (1990: 71) defines a sentence as a group of words that expresses a complete thought.
Downing and Locker (1992: 42) divide sentence into two types. They are sentence grammatically and sentence orthographically (or sentence rhetorically). The first part is the highest unit and consists of one independent clause or two or more related clauses. The second part is unit that starts with a capital letter and end with a full stop. The sentence as orthographical or rhetorical unit is associated primarily with the written language.
In conclusion, a sentence refers to the largest grammatical unit that consists of words, phrases, and clauses that present complete thought and can stand by itself.
A Simple Sentence
A simple sentence always stands as an independent sentence, which is capable of occurring on its own. A simple sentence has one subject and one verb (Werner, 1985: 227). While, Aarts and Aarts (1982: 80) say that a simple sentence is a sentence in which none of the functions is realized by a clause. It means that it does not contain subordinate sentence as realization of one of its function.
To comprehend a simple sentence, a reader has to look at the key idea or the basic message from a sentence. This key idea is made up of two parts, a simple subject and a simple predicate. So, every sentence expresses at least one key idea or basic message (McWhorter, 1986: 62). Then, Niles et. al. (1981: 149) states that a sentence consists of action and who or what is doing. It means that it has a subject or who or what is doing, and a predicate or action. These are what we call as core parts of the sentence. Niles adds that the core parts are parts that are most important to understand the meaning of a sentence.
A Compound Sentence
A compound sentence is two simple sentences connected by conjunction. According to Oshima and Hogue (1991: 157), a compound sentence is two or more independent clauses joined together by using a semicolon and a comma followed by a conjunction such as and, but, or, nor, for, yet, so, etc. They also add that there are three ways to combine independent clauses to form a compound sentence. They are:
With a coordinator
There is a comma after independent clause and then followed by coordinators. For example:
I like playing football, but I do not like playing golf.
With a semicolon
The independent clauses in a compound sentence may be joined only by a semicolon. It may occur when the two independent clauses are closely related. For example:
I read a new story; my father reads a magazine.
With a conjunctive adverb
The independent clauses of a compound sentence can also be joined by a conjunctive adverb such as furthermore, however, otherwise, and therefore. The punctuation of conjunctive adverb is quite special where a semicolon may be used after the first clause and a comma after the conjunctive adverb. For example:
The students have to take the final exam; otherwise, they will receive a grade of incomplete.
McWhorter (1986: 65) states that there are three reasons why an author combines two or more close related ideas into one sentence. The first is to clarify the ideas such as “Randy was lonely and depressed, so he called his brother on the phone to talk things over”. The second is to emphasize their connection such as “The football team practices everyday; hot or rain weather never stop them”. The last one is to show that they are equal importance. For Example: “Some students decide to take final exam, and others choose to write a term paper”. In the last example it can be seem that there are two ideas combined. So, the second idea is important as idea in the first idea. It means that we have to read the two ideas.
