Q. When would you use brackets instead of sic to correct a quotation? For example, if the original quote was “Increased cost are bad,” would you write “Increased cost[s] are bad” or “Increased cost [sic] are bad”? If it was a spoken quote (as opposed to written), would you just silently correct it?
A. The best use of sic (Latin for “thus” or “so”) after an error in a quotation of speech or text is when the passage is under scrutiny for a scholarly purpose and it’s important to point out a particular flaw or problem in the original because it’s relevant to the discussion. For example, if your original had said “Decreased costs are bad,” when it seems clear that the opposite was intended, sic would come in handy, followed by an explanation of why you suspect it’s an error. In this case, it would be dangerous to simply correct it (silently or transparently) unless you were able to consult with the writer, because the meaning is drastically changed.
Outside academe sic may be viewed as impolite. Louis Menand called it a “damning interpolation, combining ordinary, garden-variety contempt with pedantic condescension.” Resist using sic to flag an innocuous typo in a quotation (“Ha—look at this error I caught!”). Sic can also flag something that looks wrong but isn’t, and thus it may be used to sneer at readers (“Although this may look ungrammatical to those of you who don’t know any better, it’s actually correct”).
Making a correction in square brackets (cost[s]) is somewhat less aggressive than deploying a sic. A rule of thumb is to silently correct typos like the one you quote unless your judgment tells you either to be transparent or not to meddle.