Final answer:
A complete sentence must have a subject and a verb, forming an independent clause that expresses a full thought. Sentence fragments lack one of these elements or fail to form a complete thought, while run-on sentences improperly join two or more independent clauses without correct punctuation or conjunctions.
Step-by-step explanation:
Criteria for a Complete Sentence
To have a complete sentence rather than a sentence fragment, you must include both a subject and a verb. A subject is typically a noun or pronoun that the sentence is about, and the verb tells what the subject is doing. An independent clause is one that can stand alone as a sentence because it expresses a complete thought. This clause has both a subject and a verb and doesn't start with a subordinating conjunction such as 'although' or 'because' which would make it dependent.
Identifying Sentence Fragments
Sentence fragments lack either a subject or a verb, or they might have both but still not express a complete thought because they begin with a subordinating word and are not joined correctly to an independent clause. Fragments can be corrected by either joining them to a complete sentence or by revising them to include the necessary components of an independent clause.
Avoiding Run-on Sentences
Run-on sentences occur when two or more independent clauses are incorrectly joined without proper punctuation or conjunctions. They can be fixed by adding a period, semicolon, or conjunction like 'and' or 'but'.
To avoid sentence errors such as fragments, comma splices, run-on sentences, and mixed constructions, one should understand and properly use punctuation, transitions, and paragraph structure based on the relationship between ideas expressed.