Conjunctions are nice little words used to connect ideas to one another. There are three types of conjunctions: those that coordinate, joining related or similar words to each other; those that are correlative, joining words and act in pairs (like either/or); and those that subordinate, joining a subordinate clause to a main clause. Coordinating conjunctions are the most common ones and they are: for, and, nor, but, or, yet, and so. You can remember them by the acronym FANBOYS, although I’m not sure there’s any reason to worry about memorizing them. The function of a conjunction is to connect related words, phrases, and clauses. The dog ran to greet me but the ball he held was soggy. In this sentence, two separate ideas are presented: they could be separated into two sentences and the meaning of the whole shebang would be unchanged. You use a coordinating conjunction to deliberately connect slightly disparate ideas. When you want to connect disparate elements in your sentence using a coordinate conjunction, use a comma. When the connection is obvious, don’t use a comma. The dog ran to greet me and expected me to take the soggy ball. You’ll also use a coordinate conjunction when you’re making a list or series (the dog was happy, wet, and full of energy). You don’t need a comma when it’s only two items, and most publications prefer that you use the comma when listing three or more items. If your publisher follows AP style, they won’t want a series comma (or some folks call it a serial comma) before the conjunction. Correlative conjunctions join similar words and act in pairs: both/and, either/or, neither/nor, not/but, not only/but also, and whether/or. That means you won’t see one without the other. The dog ran to greet me with a ball that was neither dry nor pleasant to touch. Most of the pairs are obvious, but “neither” is a little tricky. In formal grammar, you always want “nor” with neither, not “or.” Sometimes it sounds fussy, so even fearless editors occasionally leave an “or” alone with neither. Neither and either are also singular, so if you’re negating or offering a choice among three things, you need none/or and some/and instead. None of the poodles, collies, or dachshunds wanted to play with the retriever’s soggy ball. Some of the poodles, collies, and dachshunds wanted to play with the retriever’s soggy ball. The elements that lie between correlative conjunctions should be grammatically equal and at least mostly parallel in subject matter. The dog insisted on greeting me whether or not the soggy ball was repulsive. See how the dog’s attitude is a complete sentence, and so is the part that lists the condition of that darned ball? The parts on both sides of the correlative conjunction are equal. Subordinating conjunctions join a subordinate clause to a main clause, so the parts of the sentence on either side of the conjunction won’t be equal. This means that you have a clause that helps to emphasize the important bits in the other clause: one is subordinate to the other. There’s a long list of subordinating conjunctions, and no easy way to remember them (although I don’t know why you’d want to), so I’ll just list them: after, although, as, as if, as long as, as much as, as soon as, as though, because, before, even if, even though, how, if, inasmuch, in order that, lest, now that, provided (that), since, so that, than, that, though, unless, until, when, whenever, where, wherever, and while. The dog wanted me to play with the soggy ball if he could get my full attention. In that sentence, a condition exists where the dog in the first part has an agenda. He wants my full attention less than he wants to play with the ball. If I tried it with a coordinating conjunction, it’s a little strange because both parts are not equal. The second half doesn’t seem to provide enough information to be interesting on its own. The dog wanted me to play with the soggy ball and he couldn’y get my full attention. A subordinating conjunction is always followed by a clause of some sort (adverbial or prepositional, typically). Conjunctions often act as another type of word in a given sentence, so pay close attention. Here’s an adverbial clause: The dog ran after. “After” is an adverb here because it’s how the noun behaved. This expression is an adverbial clause (not a complete sentence) because the noun (the dog) and the verb (ran) form a complete sentence. What’s left is just an adverb (after), not a proper predicate to the sentence. Here’s a prepositional clause: after Harold threw the ball. “After” is a preposition here because it tells you when the noun acted. It’s a prepositional clause because the pronoun (Harold), the verb (threw), and the noun (the ball) form a complete sentence (Harold threw the ball). What’s left is just a preposition (after), not a proper subject or predicate to the sentence. Now you can put the two kinds of clauses together and see what they’re like using the multifaceted word “after” in its role as a subordinating conjunction. The dog ran after Harold threw the ball. It looks like it might still be an adverb in this form, but it actually connects the two halves of the sentence together (The dog ran and Harold threw the ball.) Punctuation is not cut-and-dry. If the subordinate clause comes first, you probably need a comma; if it comes afterward, you probably don’t. You could also think of the subordinating conjunction as a prepositional phrase, and you always need a comma after a prepositional phrase that starts a sentence. After Harold threw the ball, the dog ran. The dog ran after Harold threw the ball. This may seem like a lot of unnecessary analysis, but if you think about it, you can see why a subordinating clause does not need a comma and a coordinating conjunction might. The dog ran, and Harold threw the ball. In that sentence, the dog’s running is less important than Harold’s ball throwing, but two complete sentences also seems like a viable option. If you leave the comma out, the second half of the sentence seems slightly more important, rendering the two halves equal. If you made the “after” sentence have a comma, you’d be hard-pressed to get the same meaning out of it: The dog ran, after Harold threw the ball. See, that way, you want to know what happened after Harold threw the ball. It isn’t a finished thought. It also makes you want to try a different comma, after Harold. Then the sentence makes no sense at all. The dog ran after Harold, threw the ball. If you want to know whether to use a comma with a conjunction, first you just have to decide whether you want to connect the thoughts or separate them. To connect two main thoughts (complete sentences of equal importance), don’t use a comma. To connect two thoughts (complete sentences of unequal importance), use a comma. To connect two thoughts (a complete sentence and a fragment), don’t use a comma. (The dog ran to Harold and gave him the ball.) To connect items in a list of three or more, use a comma. (The dog was happy, wet, and very silly.) Now, it’s time to talk about the controversy. You CAN begin a sentence with a coordinating conjunction. Oh, I know you’ve been told not to do it, but it was to prevent you from writing fragments. And some editors and publishers prefer it if you don’t start that way. But there isn’t an actual grammar rule against it. If you do it, keep a few things in mind: Place a main clause (a complete sentence) immediately after the conjunction. Start most sentences without a conjunction. Don’t use a comma after the conjunction that starts a sentence unless there’s some mitigating word.