So is known to be one of the coordinating conjunctions of English. So it can introduce an independent sentence or clause. Those are defined as containing a complete thought as opposed to the incomplete thoughts expressed by dependent sentences. I have my doubts as to whether so in the following sentence is really coordinating

I did that so he could come.

  • Is the second part considered to be sub- or coordinated or can so be a subordinating conjunction too?

  • If it is considered coordinated, doesn't that hurt the anyway suboptimal definition of what subordinate really is?

I am asking because to me "So he could come" in this example does by NO means feel independent, neither grammatically nor semantically.

  • Of course "so" can be a subordinating conjunction, and in this case it is. The sentence can be rephrased as "I did that so that|in order that he could come"
    – Vilmar
    Jan 3, 2014 at 16:12
  • @Vilmar... thanks but I think the rephrasing isn't saying much. "The door was open so I entered" can be rephrased to "The door which is why I entered"... and we have a main clause changed to a subordinate one. In my opinion, semantics should be kept out of the definitions entirely.
    – Emanuel
    Jan 3, 2014 at 16:30
  • "The door was open and I entered". Rephrasing with a more vivid example of a subordinate/coordinate conjunction helps to illustrate why 'so' in one case is subordinating, and in other coordinating.
    – Vilmar
    Jan 3, 2014 at 16:39
  • If we consider the definition "So is a subordinating conjunction when its meaning is in order that, with the purpose that", it makes sense to rephrase a sentence if you can't differentiate the conjunction type on the go.
    – Vilmar
    Jan 3, 2014 at 16:41
  • @Vilmar.. okay now I get it. I thought your point was that it is a subordinating conj.because I can rephrase the whole thing using a different sub. conj.
    – Emanuel
    Jan 3, 2014 at 17:28

2 Answers 2


There's an implied "that". "So" in this case is just the phrase "so that", shortened. It's a subordinating conjunction with "he could come" being the subordinate clause.

It can be hard to tell whether "so" is the coordinating conjunction or the shortened subordinating conjunction. Here's a litmus test: Replace "so" with "so that". Does the meaning change? If so, "so" was a coordinating conjunction.

The gas tank is empty, so I can't drive.

means that the speaker can't drive as a result of the tank being empty.

The gas tank is empty so that I can't drive.

means that the purpose of the gas tank being empty is to prevent the speaker from driving.


I did that so he could come


I did that so [that] he could come.

the clause so that he could come is in the subjunctive mode (also marked by the use of could). This is a subjunctive of purpose rather than a coordinating conjunction

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