My friend Jackie texted me a question a few weeks ago that got me thinking about the weirdness of English again. She wondered if one should prefer one of the two versions of the contraction for the phrase “it is not.” Until she asked, it had truly never occurred to me that in English, we can say either “it isn’t” or “it’s not” and both are technically correct, while offering the same meaning. Obviously, I have used both phrases millions of times in both written and spoken English, but never thought much about it.
Now that it’s been brought to my attention, I’ve had a good think on it. I realize that I tend to prefer using “it isn’t” when I am speaking and “it’s not” when I am writing. To answer Jackie’s question, I did a little research, and what I found is that in most cases either one is acceptable, but many sources say that if you want to emphasize that the answer is negative, you should use “it’s not.” It sounds sharper and places more emphasis on the negative than “it isn’t.” (So maybe when breaking up with someone, we should consider saying “it isn’t you, it’s me” rather than “it’s not you, it’s me?”)
Jackie also pointed out that this interesting situation occurs only in the present tense. The past-tense contraction is always “it wasn’t,” with no further options available. However, the double option does hold through the other personal pronouns (she isn’t/she’s not) even when you need to alter it for plural and second-person (you’re not/you aren’t, they’re not/they aren’t).
I can’t think of any other phrases or constructions in commonly-used English that offer this kind of dual-contraction situation, but if anyone else can, I’d love to hear them!