The question of when to use a comma with so vs. so that vs. so…that isn’t normally tested on any standardized test I’m familiar with, but I’ve noticed a lot of confusion about it in various people’s writing recently, and so I wanted to address it here.
Essentially, the issue is that while all three constructions involve the word so, they’re actually three different types of conjunctions, and that in turn affects how they are punctuated.
So… (pun intended), here goes:
1) So by itself – synonym for therefore
So is a coordinating (FANBOYS) conjunction that serves to connect two independent clauses (complete sentences). Like the other FANBOYS conjunctions (for, and, nor, but, or & yet), so must follow a comma when it is used this way.
Incorrect: The skin is located at the interface between our body and the outside world so its cells can respond to many different kinds of stimuli.
Correct: The skin is located at the interface between our body and the outside world, so its cells can respond to many different kinds of stimuli. (more…)