Were I in
England now, as once I was, and had but this fish
painted, not a holiday fool there but would give a
piece of silver. There would this monster make a man. (II.ii.)

Here, Trinculo imagines how, if he were in England, he could exploit Caliban’s monstrous appearance for profit. Just before these lines, Trinculo says Caliban reminds him of a fish, and here he describes how he would use a sign with a fish painted on it to attract gullible onlookers (i.e., “holiday fools”) who would willingly part with “a piece of silver” to witness the attraction. By imagining how the subjugation of Caliban would enable him to make a profit, Trinculo echoes Prospero and his imperious logic.

“Lord,” quoth he! That a monster should be such
a natural! (III.ii.)

These words also come from Trinculo, who expresses surprise that a creature like Caliban should use a term of respect like “Lord.” In saying that Caliban is “a natural,” Trinculo makes a pun on the idea that monsters are unnatural, but he also implies that Caliban is an idiot—that is, “natural” rather than cultured. Perhaps more than Caliban’s appearance alone, the disjuncture between his speech and his appearance strikes Trinculo as monstrous. Importantly, Prospero and Miranda created this disjuncture by teaching him their language in the first place. In this sense, they authored Caliban’s monstrosity.

O, it is monstrous, monstrous:
Methought the billows spoke and told me of it;
The winds did sing it to me, and the thunder,
That deep and dreadful organ-pipe, pronounced
The name of Prosper: it did bass my trespass. (III.iii.)

Alonso utters these lines in response to illusory shapes and mysterious sounds created by Ariel. His use of the word “monstrous” here is significant primarily as an example of how the European characters in the play find nearly everything on the island to be a form of monstrosity. Whereas the use of “monstrous” with regard to Caliban functions to place his humanity in question, the use of the same word to describe the strange sights and sounds conjured by magic has a subtler effect, since it suggests that Prospero—the primary conjurer himself—may himself be monstrous.