Today’s question comes from Matt Mullan, a teacher I met a few years ago at the National Council for Teachers of English convention. He writes, “I struggle to provide students with any explanation for the difference between ‘so’ used as a coordinating conjunction and ‘so’ when it’s really ‘so that’ in disguise.”
Two Sentences About Boxes, Pillows, and Cats
This really is a tricky ball of twine to unroll. We’ve even touched on the topic of whether “so” is a coordinating conjunction in episode 424, “Weird Coordinating Conjunctions: ‘Yet,’ ‘For,’ and ‘So.’”
We didn’t pursue the matter too far in that episode, but you better believe we’re going to in this one! To understand Matt’s question, let’s think about two sentences that on the surface are a lot alike. One is “Kim put a pillow on top of the empty box, so no cats would get into it.” The other one is “Kim put a pillow on top of the empty box, so no cats got into it.” The words are exactly the same, except that where one of them has “would get,” the other one has the verb “got.”
‘So That’ Showing Purpose: A Subordinating Conjunction
Let’s take a closer look at the first sentence, “Kim put a pillow on top of the empty box, so no cats would get into it.” The clause that begins with “so” expresses Kim’s purpose: Kim didn’t want any cats to get into the empty box. Notice that you can replace “so” with the somewhat stuffier phrase “in order that,” and the sentence means the same thing: “Kim put a pillow on top of the empty box, in order that no cats would get into it.” For this reason, it will be convenient to talk about the “so” in this sentence as the “purpose-‘so.’”
Here’s something else you can do with this sentence: You can put the “so” clause first, and the sentence will still be grammatical. In other words, we could also say, “So no cats would get into the empty box, Kim put a pillow on top of it.”
This ability to come before or after a sentence’s main clause is a dead giveaway that we’re dealing with an adverb clause. An adverb clause is a clause that explains when, where, how, or why the action of the main clause happens. Adverb clauses are a kind of clause known as a subordinate clause, and subordinate clauses always begin with a subordinating conjunction. One of the best-known subordinating conjunctions is “because,” so let’s see how this flexible ordering works with a “because” clause. The sentence “No cats got into the empty box, because Kim put a pillow on top of it” could also be phrased, “Because Kim put a pillow on top of the empty box, no cats got into it.”
Another subordinating conjunction is “in order that,” which we were just talking about a minute ago. (That’s right, subordinating conjunctions can consist of sequences of words in addition to individual words.) We know this because we can put a clause beginning with “in order that” at the beginning of a sentence, just like we did with a clause beginning with “because”: “In order that no cats would get into the empty box, Kim put a pillow on top of it.” The fact that the clause “so no cats would get into it” is also able to come at the beginning of a sentence is evidence that it, too, is an adverb clause, and that purpose-“so” is a subordinating conjunction.
Another reason to believe that purpose-“so” is a subordinating conjunction is that it can be replaced by “so that,” which is definitely a subordinating conjunction. We know this the same way as we do for “because” and “in order that”: We can put a “so that” clause before or after the main clause. We can say either “Kim put a pillow on top of the empty box, so that no cats would get into it,” or “So that no cats would get into the empty box, Kim put a pillow on top of it.”
At this point, it makes sense to conclude not only that purpose-“so” truly is a subordinating conjunction, but also that it and “so that” are actually the same subordinating conjunction. This is what Matt meant when he said that “so” is sometimes “so that” in disguise. Why does it sometimes come along with a “that” and sometimes not? Well, it’s just one of the facts about English that we can sometimes omit the word “that.” For more on that topic, check out episode 601, which we’ll link to in the show notes.
Here’s what we have so far: Purpose-“so” is a subordinating conjunction, and can be thought of as a “so that” with the word “that” omitted. The clause it introduces can come before or after the main clause in a sentence. Typically, this clause will use a modal auxiliary verb, such as “may,” “might,” or “would,” since these verbs are good for talking about situations that are not true yet, such as purposes.
‘So’ Showing Result: A Coordinating Conjunction
Now let’s return to our other sentence: “Kim put a pillow on top of the empty box, so no cats got into it.” This “so” clause expresses a result. Notice that you can replace the word “so” with the words ”and as a result,” and the sentence has the same meaning: “Kim put a pillow on top of the empty box, and as a result, no cats got into it.” For this reason, it will be convenient to talk about the “so” in the this sentence as the “result ‘so.’”
Unlike the purpose-”so,” if we try to put the result-“so” clause first, the sentence becomes ungrammatical: “So no cats got into the empty box, Kim put a pillow on top of it.” Now in case you’re thinking that that sentence doesn’t sound so bad, make sure that your result-“so” hasn’t sneaked away and been replaced by a purpose- “so.” The temptation, at least for me, is to unconsciously interpret it as a purpose clause once again, and think how it would sound better with “would get” instead of “got.” But when I remind myself that “so no cats got into the empty box” is telling what actually happened, the sentence crashes.
This inability of the result-“so” clause to come before the clause it’s connected to indicates that result-“so” is not a subordinating conjunction, but a coordinating conjunction. The best-known coordinating conjunctions are “and,” “but,” and “or,” and just as with result-“so,” the clauses they introduce have to come after the main clause. For example, we can say, “Kim put a pillow on top of the empty box, and no cats got into it,” but when we try to swap the two clauses, it becomes ungrammatical: “And no cats got into the empty box, Kim put a pillow on top of it.”
To sum up this second batch of facts: When “so” expresses result, it is a coordinating conjunction. The clause that it introduces has to come after the main clause, and because it is not talking about hypothetical situations, it typically does not use a modal auxiliary verb such as “may,” “might,” or “could”: “No cats got into the empty box.”
‘So That’ Showing Result: An Unclear Picture
Wouldn’t it be nice if these two constellations of facts were the whole story? Purpose-“so,” which sometimes shows up as “so that,” is a subordinating conjunction. Result-”so” is a coordinating conjunction.
Unfortunately, there’s more. As it turns out, “so that” can also express result. Using the same example we’ve been using so far, we could say, “Kim put a pillow on top of the empty box, so that no cats got into it.” Notice that we’re using the ordinary past tense verb “got,” not “would get” or “could get.” In other words, after Kim put that pillow in place, no cats were able to sneak into that box, curl up inside it, and start shedding fur. But it’s not entirely clear whether this sentence is expressing Kim’s purpose for putting a pillow on the box, or a result of Kim’s doing that, since really, both things could be true. To show that “so that” really can be used to show result without purpose, we need a different example. Here’s one from an online technical support forum: “I accidentally shifted a right hand page so that it no longer aligns with the facing page in my layout.” The word “accidentally” makes it clear that the “so that” clause is expressing only a result, not the writer’s purpose.
Another thing to note about “so that” clauses that show result is that they don’t sound very good when you omit the word “that.” If we say, “I accidentally shifted a right hand page so it no longer aligns with the facing page in my layout,” it doesn’t make sense. Going right into the “so” clause without a pause makes it sound like a purpose clause, but the word “accidentally” undermines this interpretation.
It seems to me that when a listener hears “so that,” they’re prepared for either a purpose clause or a result clause, and they will let the context guide them in the right direction. But with just plain “so,” they expect a purpose clause, because if the speaker wanted to express a result with just plain “so,” the best choice for that job would be the coordinating conjunction “so.”
The question now is whether this result-oriented “so that” is a coordinating or subordinating conjunction. It consists of two words, which suggests it’s a subordinating conjunction. If it were a coordinating conjunction, it would be the odd one out in a family whose other members are all single words: “and,” “but,” “or,” “nor,” “yet,” “for,” and result-“so.”
On the other hand, “so that” showing result is different from the other subordinating conjunctions we’ve talked about, because the clause it introduces can’t come at the beginning of a sentence. The sentence “So that a right hand page no longer aligns with the facing page in my layout, I accidentally shifted it,” doesn’t make sense. Just as it did when we took out the word “that,” it now sounds like a purpose clause, but the word “accidentally” contradicts this interpretation. But that’s OK. We didn’t say that all adverb clauses can come before a main clause; we just said that if a clause can do that, it’s definitely an adverb clause.
If that sounds confusing, here’s an analogy that’s easier to think about. If your family pet is a poodle, your family pet is a dog. But that doesn’t mean that if your family pet is a dog, it’s a poodle. It could be a golden retriever, a bulldog, or a friendly mutt from the pound. The upshot of all this is that “so that” is still a subordinating conjunction, even when it introduces a result clause.
‘So’ and Sentence Fragments
Now that we have a clearer idea of what kind of words “so” and “so that” are, what does that mean for how we write a sentence with them?
One area that the nature of “so” and “so that” effects is in avoiding sentence fragments. We’ve seen that adverb clauses can come before or after a main clause, but the important thing to remember is that either way there will be a main clause to make a complete sentence. The clauses “So that no cats would get into it” and “Because Kim put a pillow on top of the empty box” are OK as spoken answers to questions, but in written English, they have to partner up with a main clause in order to make a complete sentence. By the way, this is why you may have been told that you shouldn’t start a sentence with “because”: If you do, you have to remember that the sentence isn’t complete until you get that main clause in there. If you put the main clause first, and the “because” clause second, you don’t have that problem. But it actually is OK to start sentences with “because.” You just have to be careful.
On the other hand, clauses that are introduced by a coordinating conjunction do not have to have another clause in the same sentence. If you want to, you can take a coordinating conjunction and just one clause, and have a complete sentence. It’s slightly more casual if you do this, but it’s grammatical. Here’s how it would sound with our example, using the coordinating conjunction “and”: “Kim put a pillow on top of the empty box. And no cats got into it.” Here it is with the coordinating conjunction “so”: “Kim put a pillow on top of the empty box. So no cats got into it.” For more about beginning sentences with subordinating and coordinating conjunctions, check out episode 418.
By the way, we’ll put links to all the other episodes about coordinating conjunctions in the show notes.
‘So’ and Punctuation
Another issue affected by what kind of “so” you’re using is punctuation. In particular, should you put a comma before “so”? This question only comes up when your “so” clause comes later in the sentence, because if it comes at the beginning of a sentence, then the punctuation that comes before it is whatever punctuation ended the previous sentence!
For subordinate clauses, the rule is that you usually don’t put a comma before them. However, this rule is more of a guideline. If the “so” clause seems long, you might want to put a comma before it. The examples we’ve been using are rather long, so I’ve been putting a comma before every “so” clause that comes later in a sentence.
You might also put a comma before a “so” clause if it follows a long or complex main clause, to show that the “so” clause modifies an earlier verb rather than a later one. For example, take the sentence “Kim told Sandy to invite Robin so no one’s feelings would get hurt.” What action had the purpose of respecting people’s feelings? Inviting Robin, or telling Sandy to invite Robin? Without a comma, people will tend to think the “so” clause modifies “invite Robin.” However, if we use a comma, the sentence turns into “Kim told Sandy to invite Robin, so no one’s feelings would be hurt.” Now it sounds like the “so” clause modifies “Kim told Sandy.”
For coordinating conjunctions that join clauses, the rule is that you usually do put a comma before them. But this rule, too, is more of a guideline: If the two clauses are very short, you can leave out the comma. For example, “It started thundering and we had to take shelter.” This means that before the coordinating conjunction “so,” you should probably put a comma unless your sentence is really short.
We’ve talked about putting commas before “so,” but what about after it? This one is easy: No! If we’re dealing with purpose-“so,” the subordinating conjunction, remember that it’s a “so that” in disguise, and in written English, we don’t put a comma between a “that” and the clause it introduces.
If we’re dealing with result-“so,” the coordinating conjunction, there’s more room for confusion, because many people do put commas after coordinating conjunctions that come at the beginning of a sentence. This is probably because it’s common to put a pause here in spoken English. For example, I might say something like, “I wanted to bake a cake for the party, but…I discovered I was out of flour.” Even so, in standard written English, the rule is not to put a comma after a coordinating conjunction, unless there’s some kind of interruption between the conjunction and the rest of the sentence. For example, we might write, “Kim put a pillow on top of the empty box, so, in case any curious cats came prowling around later, they wouldn’t get into it.”
Summing Up
So…here’s a summary of what we’ve covered today.
First, the subordinating conjunction “so that” can show purpose. Clauses beginning with this subordinating conjunction usually, but not always, contain a modal verb such as “might,” “could,” or “would.” These clauses can come before or after a sentence’s main clause. You have the option of omitting the word “that” for this subordinating conjunction, and you probably don’t need a comma before it. “So that” is a subordinating conjunction in our sentence “Kim put a pillow on top of the empty box so that no cats would get into it.”
Second, the subordinating conjunction “so that” can also show result. These result clauses usually don’t use modal verbs. Result clauses beginning with “so that” are different from other adverb clauses in two ways: They can’t come before a sentence’s main clause, and you can’t omit the “that.” But like other adverb clauses, they don’t need a comma before them. “So that” is a subordinating conjunction in the sentence “I accidentally shifted a right hand page so that it no longer aligns with the facing page in my layout.”
Third, the coordinating conjunction “so” shows result. Like other result clauses, clauses beginning with result “so” usually don’t use modal verbs. Like other clauses that begin with a coordinating conjunction, they are independent clauses, which means they can stand alone, or after another independent clause in a single sentence. When they’re part of a larger sentence, you probably need a comma before them. “So” is a coordinating conjunction in our sentence “Kim put a pillow on top of the empty box, so no cats got into it.”
So there you have it! Matt, thanks for a great (and kind of difficult) question.
Neal Whitman is an independent PhD linguist who blogs at literalminded.wordpress.com. You can also find him on Twitter as @LiteralMinded.
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