Another punctuation rule baffled consultants: using a comma before FANBOYS (the acronym for the coordinate conjunctions, for, and, nor, but, or, yet, and so) joining two independent clauses.
These questions focused on two rules famously derived from Latin: Latin coordinate conjunctions join, so they cannot be placed at the beginning of a sentence; a Latin preposition precedes its object, so it cannot end the Latin sentence and, by extension, the English sentence as well.
Or you can join the clauses with one of the six coordinate conjunctions: and, but, or, for, yet, nor.
We now abuse the rule on "so" shamelessly, and the word seems well on its way to joining the list of coordinate conjunctions. But many purists would argue that the following is technically a run-on: "'All the neighborhoods are starting to work together, so we're not just moving the problem from place to place,' he said." As with any other sort of comma splice, you can avoid the error by breaking the run-on into two sentences.