Sentence structure problems.
Sentence fragments:
Sentence fragments are acceptable sometimes in writing other than college essays where they are usually forbidden. Most fragments are an accident and should be fixed. How can you tell if a sentence is incomplete? Check very short sentences to make sure there is a subject and predicate (a verb plus its auxiliaries and modifiers). A short sentence can be complete (“Jesus wept.” From the King James version of the Holy Bible, is a complete sentence and is, thank God, grammatically correct). But note the following paragraph:
“It’s next to impossible to get anywhere fast. With a traffic light on every other corner, that seems to go from red to green and back again every two minutes. With twice as many retail outlets than we really have use for. Not to mention the average speed is less than 15 mph. Division street is a lousy substitute for a freeway.”
The writer needs to check each sentence and make sure there’s a subject, verb and auxiliaries included. Note that the “traffic light” sentence above has neither a subject nor a verb the way it is phrased. If one substitutes “There is” for “With a”, then it is complete (with some other fine tuning):
“There is a traffic light on every other corner that seems to change from red to green and back again every two minutes.”
Run on sentences: This is actually a punctuation problem. If you write two independent clauses in a row (complete sentences), make sure the punctuation between them is a semi-colon or period. The following is a run-on and is incorrect:
George brought his boa constrictor to class, it swallowed Ralph’s backpack.
Here are two correct versions:
George brought his boa constrictor to class; it swallowed Ralph’s backpack.
George brought his boa constrictor to class. It swallowed Ralph’s backpack.
Long sentences can be punctuated and developed so they are not run ons. See the advice on “Sentence Variety”.