Writers Talk About Writing
Your Head Will Spin: "Naught," "Aught," and "Ought"
If someone says "I know aught about football," the amount of knowledge could be a lot or nothing. That's because "aught" can mean "everything," or "zero."
In British English, it often means "all," as in "for aught I know, football uses a round ball." In the US, it more commonly means "nothing." Garner's Modern American Usage says that was originally a mistake. "By error," Garner's says, "a nought (= a zero) was widely misconstrued as an aught. Thus, aught has come—mistakenly—to bear the sense ‘zero.'" Someone saying "I was born in aught eight" might be British, where "aught" is fairly common for "zero"; old-fashioned; just old; or from an area of the US where "aught" is dialect. And, of course, there's the "aught," "double-aught," and "triple-aught" that designate the size of the buckshot in a shotgun shell.
Garner's says "aught" for "zero" is fully standard English. But be aware that Brits, in particular, might be saying something greater than zero, so you "ought" to avoid it unless the context is crystal clear.
"Ought" is also a variant spelling of "aught," mostly in British English, but most of the time, it means "should." You can tell when it's being used in the sense of an obligation, because it's usually accompanied by the infinitive form of another verb: "You ought to know more about football." As a negative, though, there's "aught" reason to use it: As a usage note in The American Heritage Dictionary of English says: "Usages such as He hadn't ought to come and She shouldn't ought to say that are common in many varieties of American English. They should be avoided in written English, however, in favor of the standard ought not to."
Then there's "naught." It also means "nothing," though many dictionaries say that usage is archaic or restricted to literary uses. It most often appears in phrases like "His studying was for naught, since he flunked." "Naught" is also considered a variant spelling of "nought," and sometimes either one can be correct: Webster's New World College Dictionary says that a battleship can be either a "dreadnaught" or a "dreadnought." (Most other dictionaries prefer the "naught" spelling.) Of course, it's the heavily armed warship that "dreads nothing," not the people facing down its guns.
And if you're wondering, yes, "naughty" is derived from "naught," as in someone who has "naught" morals or manners. But "naughty" originally meant "poor," someone who had "naught."
As a rule of thumb, "nought" (or "aught") is preferred when dealing with numbers, while "naught" is preferred outside of math. "I ought to know better, but I know naught about the difference between aught and nought" is a sentence sure to make more than one head spin.