A run-on or fused sentence is a sentence consisting of two independent clauses that are not properly joined by appropriate punctuation, or a conjunction (such as “and”, “but”, “or”, “so”, “yet”, “because”). An independent clause can be identified as having a subject and a predicate and stands by itself as a complete sentence. The subject can be something like “John” or “he” or “his father”. The predicate is the rest of the clause and includes a verb.
A typical example of a run-on sentence is where a pronoun connects the second clause back to the first. An example is: “John studied every day he wanted to pass his exams.” This sentence has two independent clauses, the first being “John studied every day” and the second being “he wanted to pass his exams”. Each one stands by itself but they are fused together. The sentence is actually two separate sentences. To make it into one correctly constructed sentence, it needs a conjunction. In this case, a conjunction such as “as” or “because” could be inserted between the two clauses. The sentence becomes: “John studied every day as he wanted to pass his exams.” Alternatively, two separate sentences could be formed: “John studied every day. He wanted to pass his exams.”
A commonly seen run-on or fused sentence is where one of the independent clauses recommends some sort of action. For example: “The exams are coming up, you should now be studying hard.” Note in this example that a comma has been used. It is something that is often seen in run-on sentences. This particular type of run-on sentence is called a “comma splice”. Thus if two independent clauses are linked by a comma, they still form a run-on sentence.
Another easily spotted run-on sentence is where the clauses are linked by a word such as “however” or “nevertheless”. For example: “The exams were only two weeks away, however John hadn’t started studying yet.” Again, there are two independent clauses here and no conjunction. The punctuation is also incorrect. To make this sentence correct, replace the comma after “away” with a semicolon, and a comma after “however”. Alternatively, “however” could be replaced by “and” and no punctuation would be required. Or, the sentence could start with “Although”, and delete “however”.
A run-on sentence can be any length. For example, “John ran she followed” is a run-on sentence. Here’s a longer example: “Community service is where offenders work on some organized project for the benefit of the public it is an alternative to jail for certain types of law-breakers.” This sentence could be broken into two or have a conjunction added. A better alternative might be to change the sentence around a bit and introduce a dependent clause. Thus the sentence could be rewritten as: “Community service, which is an alternative to jail for certain types of law-breakers, is where offenders work on some organized project for the benefit of the public.” The middle part of the sentence (between the commas) is a dependent clause; the rest is an independent clause.
In summary, to spot a run-sentence, ask yourself whether the sentence has two independent clauses (that is, where each clause is actually a sentence). If it doesn’t, then it won’t be a run-on sentence. Where it does, look to see if there is a conjunction between the clauses. If there is, it’s not a run-on sentence. If there isn’t, consider any punctuation between the clauses. A semicolon, colon or dash should mean it’s not a run-on sentence. On the other hand, if there’s a comma or no punctuation, it’s a run-on sentence.