Word processing programs are wonderful things. I have always been a not-so-stellar speller. By running whatever they write through the spelling corrector function on MSWord, anyone (including me) can weed out all spelling mistakes in their writing, right? 

Wrong. 

I certainly hope everyone understands the difference between "it's" and "its", and will skip the next paragraph, because as a native English speaker (as I am assuming most of the people who come visit this site are), you are in seriously bad shape if a Japanese national is informing you of English grammar and usage.

Its and it's are pronounced the same (duh) but are completely different words. "Its" is the possessive form of "it", that is, "its" is the gender-free equivalent of "his" or "her". "It's" is a contraction for "it is". 

Got it?

Are you sure? 

I ask this because I have read things written by so many people who do not seem to understand the difference. "Its" and "It's" are both correctly spelled, genuine English words, and MSWord (and probably every other commercially available word processing program) isn't even going to blink at either of them, which is probably why I see one where the other should be as often as I do. 

Another one that gets interchanged quite a bit is "your" and "you're". The former is, of course, the possessive form of the second person pronoun, and the latter is a contraction of "you are". This error is another one that the spelling correction function would overlook. 

I'm not uptight about grammar. You will notice that I end sentences with prepositions and pepper my writing with slang. (I also use "you" in sentences that aren't surrounded by quotation marks, which is, IIRC, another no-no. I think. It's been years since I've actually paid attention in English class. Come to think of it, it's been years since I've taken English class.) But I truly believe that a person's written words give you insight on the level of his intelligence, and using the wrong word in the wrong place doesn't earn you any intelligence points. 

Please use "its" and "it's" and "your" and "you're" correctly. You're a smart person, show me you're a smart person. 

And if you're not, watch your usage, and fool me into thinking you're a smart person.