You probably remember a few rules about spelling from your elementary school days. The poem that most students deem unforgettable is this one:

I before e, Except after c, Or when sounded as a, As in neighbor or weigh.

That's certainly a helpful mnemonic — most of the time. It works for words such as beige, ceiling, conceive, feign, field, inveigh, obeisance, priest, receive, shield, sleigh, and weight.

But take a look at these words that don't follow the rule from the poem: ancient, caffeine, codeine, conscience, deify, deity, efficient, either, feisty, foreign, forfeit, height, heist, kaleidoscope, leisure, nucleic, protein, reimburse, reincarnation, science, seize, sleight, society, sovereign, species, sufficient, surfeit, and weird.

You see enough exceptions to wonder about the rule, don't you?

Here are some rules that generally apply to English nouns. (Note the word generally.) English has adopted words from many languages, and those languages have differing ways of changing word forms. That means, unfortunately, that every rule will have an exception (and probably more than one, as you've seen). Although the whole enchilada can be pretty confusing, these rules provide you with some useful guidelines for making your spelling decisions.