All those rules you learned about the English language while you were a kid (and even as an adult), are probably wrong, misguided, or just plain non-existent. English is a wonderful mish-mash of many influences, and it doesn't neatly adhere to any set of regulations that fit other languages. That's its beauty.
The people at Language Log have long been debunking certain steadfast rules that supposedly govern word usage in English, and Geoffrey K. Pullum continues that tradition with today's post about a website called The Apple that has a list called "11 Grammar Mistakes to Avoid".
Here's a sample of Pullum's critique:
4. The fourth is headed "Less vs. Fewer", and warns against substituting less for fewer. It is claimed that the latter "describes finite, listable items". Strictly that would imply that it's ungrammatical to say There are fewer rational numbers than reals, because neither the rationals nor the reals are finite in number, and the reals are not even listable. But never mind the math. The page recommends saying "fewer brains", as in "He has fewer brains than I thought", which is ludicrous (how many more does he need, if he has one?). It's an old, old usage quibble, and here it's very badly presented and described.
If you like to write, and if you are truly concerned with improving your writing while not submitting blindly to phantasmal language laws, give Pullum's list a read, and then poke around a little more on the Language Log website. And remember, when it comes to English, take all rules with a creative grain of salt (even this one).