I just don't get how some grammar is considered correct, while in other circumstances it's a run-on sentence. I also don't understand how sometimes a semicolon is necessary while other times, it's perfectly okay to use a comma. For example, "If you examine a document you have written recently, you are likely to find many such sentences; they’re so common that you don’t even realize you are writing them." Why is there a comma after 'recently,' if there are no conjunctions to connect the sentences. Wouldn't that be considered a run-on sentence? Also why is there a semicolon after the word 'sentences' and not a comma or period? I do not understand.
"If you examine a document you have written recently" is a dependent clause, basically meaning it depends on the main clause, "you are likely to find many such sentences," to work properly. It cannot stand on its own. Commas usually separate these clauses from the main clause (with a few exceptions), especially if they are considered parenthetical elements. The comma is not being used as a semicolon or a conjunction here, but basically a pause. There is some debate about the semicolon. You use it when you need more than a comma and less than a period, though it can assume either role. It usually functions as a conjunction between two independent clauses, though some will claim that you should only use one as a conjunction if the two main clauses it binds are closely related. Others will argue that you should use semicolons if the sentences are filled with a lot of internal punctuation, such as a series, dependent clauses, etc. Semicolons can be used with conjunctions in the same manner that commas can (e.g. Sentence here; and sentence here), but they don't require conjunctions. The semicolon has more functions than that, too, but I hope that explains your question. The example you've written is not a run-on sentence; it's grammatically correct.
Okay, I know what you're saying. Thank you for replying, that has always confused me. Slowly but surely, I'm learning how to use commas properly.
I have a useful document on this. Can I attach Word.docs here? This is the image... I can email you a bigger version, if there are no suggestions as to how to attach the doc.
Words like "when," "if," "after," when they start a sentence often turn the clause into a starting phrase. When I met her at the office, I brought my lawyer. If she becomes violent, my body guard will handle the situation. After a long day, I like to soak in the hot tub. Sometimes the comma doesn't seem necessary. When she runs her feet flop. Europeans would rarely use a comma in the above sentence. In fact, they seem to often not set of starting phrases with commas. I try to avoid semicolons. It's usually better to use a full stop or combine the sentences in another way.
