The word in some form is used around eighty times in Twelfth Night. Almost every one of the main characters is at some point called a fool, an ass, or mad. There those who are born fools, those who achieve foolishness, and those who have foolishness thrust upon ‘em …
Feste, of course, is the Clown, the Fool, sometimes glancingly the madman: not someone to judge your sanity against. He’s educated, and intelligent, and shows himself to be wiser than most of them, but:
How dost thou?
Truly, sir, the better for my foes and the worse for my friends … Marry, sir, [my friends] praise me and make an ass of me; now my foes tell me plainly I am an ass, so that by my foes, sir, I profit in the knowledge of myself, and by my friends I am abused.
(Sir Topas is called one of “such asses” by Malvolio, but he was meant to be so.)
He has achieved foolishness.
It is, in fact, his job.
Sir Andrew, also of course: “a very fool”, says Maria, and “many men do call me fool” he says himself. He’s simply not very bright, poor fellow, and in most performances knows it, but tries to keep up. Basically everyone that speaks of him calls him a fool. He is a “natural fool” – brainless – as opposed to an allowed fool, someone whose job it is. His own opinion is that he’s not such an ass he can’t keep his hand dry … I haven’t found such an interpretation of that phrase anywhere (it is given by at least one website as meaning that he knows to keep in out of the rain, basically), but my first thought on hearing the line was that he was capable of peeing without getting his hand wet – he had that much control. *shrug* Or not. Depending on the interpretation, he’s quite the wit and urbane knight, in his own mind … or he knows full well that he’s … off.
He was born foolish.
Malvolio, of course yet again: Feste reflects the term back at him. And of course at the end, Olivia: “Alas, poor fool!” Maria calls him “an affectioned ass”. He is what is usually called book-smart, sort of, though Mary says that’s a sham (though he is able to come back with Pythagoras’s theory about one’s grandam). (Feste also calls him “goodman drivel”, which is kind of awesome.)
He’s had foolishness thrust upon ‘im – partly. He has the trifecta, though: he was also born foolish, and achieved foolishness …
Viola: Olivia’s will is pulling counter to Orsino’s, which is pulling counter to Viola’s and Olivia’s both; Olivia would make Viola/Cesario what she wants her/him to be. Wouldn’t that be better? “I wish it might, for now I am your fool.” Thrust upon.
(In Olivia’s speaking to Cesario, it is at this point that s/he becomes “thou” from “you”)
Olivia: “Take away the fool” – Feste proves her a fool, and he’s not altogether wrong. Also, “I’m as mad as [Malvolio], if sad and merry madness equal be!” She’s scattered by a strong wind – she’s been thrust upon. Thoroughly.
Sir Toby: also called a fool by Feste – a drunken man (which Toby very much always is) is like a fool, a madman, and a drowned man. Toby is also a madman: “He is but mad yet”, not drowned. And sparring against Malvolio is “in admirable fooling”. Olivia: he “speaks nothing but madman”. He achieves foolishness, largely in drink.
Orsino: obliquely, by Feste, a fool: “the Lady Olivia has no folly: she will keep no fool, sir, till she be married; and fools are as like husbands as pilchards are to herrings; the husband’s the bigger”. He has the reputation of being “A noble duke, in nature as in name”, but lately he’s been … distracted. He has achieved foolishness.
Antonio: Orsino – “What foolish boldness brought thee to their mercies?” And he considers himself a fool for having been taken in by Sebastian. Soldier: “The man grows mad.” Orsino: “Thy words are madness.” Thrust upon. Poor bugger.
Sebastian: Decides either he must be mad or Olivia is, and as Olivia does not appear to be it must be he. Thrust upon.
Maria: One of the only ones not the direct recipient of a crazy tag. But Malvolio includes her with Sirs Andrew and Toby, and Feste – “Are you mad, or what are you?” Including her in his general censure was not entirely fair, but that’s Malvolio. Achieved.
And for whoever might have been left out in Illyria (Fabian, perhaps, and Maria who was not singled out elsewhere), Sebastian gave one all-encompassing cry: “Are all the people mad?” Which, to him, they were.