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When you want to use commas and semicolons in sentences and when you are concerned about whether a sentence is or is not a fragment, a good way to start is to be able to recognize dependent and independent clauses. The definitions offered here will help you with this.
Independent Clause
An independent clause is a group of words that contains a subject and verb and expresses a complete thought. An independent clause is a sentence.
Jim studied in the Sweet Shop for his chemistry quiz.Dependent Clause
A dependent clause is a group of words that contains a subject and verb but does not express a complete thought. A dependent clause cannot be a sentence. Often a dependent clause is marked by a dependent marker word .
When Jim studied in the Sweet Shop for his chemistry quiz . . . (What happened when he studied? The thought is incomplete.)
Dependent Marker Word
A dependent marker word is a word added to the beginning of an independent clause that makes it into a dependent clause.
When Jim studied in the Sweet Shop for his chemistry quiz, it was very noisy.Some common dependent markers: after , although , as , as if , because , before , even if , even though , if , in order to , since , though , unless , until , whatever , when , whenever , whether , and while .
Connecting independent clauses
There are two types of words that can be used as connectors at the beginning of an independent clause: coordinating conjunctions and independent marker words.
1. Coordinating Conjunction
The seven coordinating conjunctions used as connecting words at the beginning of an independent clause are and , but , for , or , nor , so , and yet . When the second independent clause in a sentence begins with a coordinating conjunction, a comma is needed before the coordinating conjunction:
Jim studied in the Sweet Shop for his chemistry quiz, but it was hard to concentrate because of the noise.
2. Independent Marker Word
An independent marker word is a connecting word used at the beginning of an independent clause. These words can always begin a sentence that can stand alone. When the second independent clause in a sentence has an independent marker word, a semicolon is needed before the independent marker word.
Jim studied in the Sweet Shop for his chemistry quiz; however , it was hard to concentrate because of the noise.
Some common independent markers: also , consequently , furthermore , however , moreover , nevertheless , and therefore .
Connecting dependent and independent clauses
Subordinating conjunctions allow writers to construct complex sentences, which have an independent clause and a subordinate (or dependent) clause. Either clause can come first.
The students acted differently whenever a substitute taught the class. Whenever a substitute taught the class, the students acted differently.Note that the clauses are separated with a comma when the dependent clause comes first.
Some common subordinating conjunctions: after , as , before , once , since , until , and while .
Comma Splices
A comma splice is the use of a comma between two independent clauses. You can usually fix the error by changing the comma to a period and therefore making the two clauses into two separate sentences, by changing the comma to a semicolon, or by making one clause dependent by inserting a dependent marker word in front of it.
Incorrect: I like this class, it is very interesting.Fused Sentences
Fused sentences happen when there are two independent clauses not separated by any form of punctuation. This error is also known as a run-on sentence. The error can sometimes be corrected by adding a period, semicolon, or colon to separate the two sentences.
Incorrect: My professor is intelligent I've learned a lot from her.Sentence Fragments
Sentence fragments happen by treating a dependent clause or other incomplete thought as a complete sentence. You can usually fix this error by combining it with another sentence to make a complete thought or by removing the dependent marker.
Incorrect: Because I forgot the exam was today.