Southern Illinois University Edwardsville
URL: http://www.siue.edu/IS/WRITING/
Published by: Instructional Services Department
Last Updated: August 22, 2005 
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FRAGMENTS result when a group of words lacks an independent subject and/or verb:   Joe, my pal.  (no verb)
                Walked three miles.  (no subject)

To be a sentence, a group of words must contain a subject and a verb that are independent, that is, that can stand alone as a complete thought:

                S-V.   This is the symbol for an independent clause.

                                Birds sing.
                                Cows give milk.
                                The weather is pleasant.

Problems identifying independent subjects and verbs:
                1.  A phrase is not a sentence:
                                Prepositional phrase fragments:
                                                On the other side of the swift-rushing river.
                                                By the time of the game.
                                Verbal fragments:
                                                Running the business. (participial phrase)
                                                To earn a lot of money. (infinitive phrase)
                2.  A dependent clause is not a sentence:
                                After the party was over.
                                When the clock struck one.

COMMA SPLICES result when two independent clauses are spliced together with a comma.
                Comma Splice Pattern:                                         Sentence Patterns:

                          S-V,  S-V.                                                              S-V  .  S-V.
                                                                                                         S-V  ;  S-V.

You can join two independent clauses together with a comma if you use a coordinate conjunction:  
        The pattern is
                      S-V, and/or/but/nor/for/yet/so S-V.
           Mother left early, but Father was late.

You can join a dependent clause (starts with words like where, when, because, etc.) to an independent clause with a comma:
                When the rain stopped, we left the cabin.

You must use a semicolon (;) to join independent clauses with conjunctive adverbs.  Using a comma [,] creates a comma splice.

The pattern is           S-V ;   however,         S-V .
                                               therefore, etc.
Conjunctive adverbs are usually followed by a comma because they are interrupters.