Misuse of “It’s” Versus “Its” “Sets Off Pavlovian ‘Kill’ Response”

Grammar guru Lynne Truss reminded me of the location of my “last nerve”, at least regarding mispunctuation (I checked – it’s in the Random House Dictionary), in the February 27, 2009 entry of my Eats, Shoots & Leaves 365-day calendar. Ms. Truss does not mince words when she states:

The confusion of the possessive “its” (no apostrophe) with the contractive “it’s” (with apostrophe) is an unequivocal signal of illiteracy and sets off a simple Pavlovian “kill” response in the average stickler.

I know it’s not cool to respond to an email which enthusiastically announces, “You’ve got to come to this very important meeting. Its next Wednesday at my house, which has it’s own hot tub big enough to seat eight!” with a blunt “Don’t write. You’re an illiterate. (But can I come sit in your hot tub anyway?)” -- but when you’re an average stickler foaming at the mouth, it’s an almost irresistible temptation.

Simple tests: Does the sentence make sense if you replace “it’s” with “it is”? Does the sentence make no sense if “its” is not replaced with “it is”?