Punctuating “So”

The distinction between “so” to mean “therefore” and “so” to mean “in order that” often goes unmentioned in ESL books, yet the two words require different punctuation. “So” the conjunction that expresses an expected result is a coordinating conjunction (one of the words comprising the mnemonic FANBOYS), and requires a comma to precede it, as such. “So” the subordinating conjunction that means “in order that,” like other subordinating conjunctions, does not require a comma before it, unless the information that follows expresses a contradiction or contrast.