Why does the Prince of Arragon choose the silver casket in The Merchant of Venice?
After careful deliberation in which he concludes that he is quite deserving of Portia, the Prince of Arragon chooses the silver casket.
Convinced that he deserves Portia, the Prince of Arragon goes through a line of reasoning not unlike that of the previous suitor. He rejects the gold casket because he thinks that only those shallow men who value appearances over other qualities would select the gold. Further, he rejects the lead casket as unfitting for Portia, and it is not beautiful enough for him to risk himself for it.
When he looks at the silver casket, the prince reads on it, “Who chooseth me shall get as much as he deserves” (2.9.51). Believing that he is quite deserving of Portia, the prince then selects the silver casket. However, he is wrong, as inside the silver casket is a fool's head, suggesting that the prince has been foolish to presume that he does deserve Portia. This suggestion greatly angers the prince, but he honors the pledge that he has made, which stipulates that if he loses, he will not reveal which casket he has chosen, he will not marry, and he will immediately depart.
The Prince of Arragon is the second suitor to come try for Portia's hand (the second one we see in the play, anyway), in Act 2, Scene 9. Like the Prince of Morocco, the Prince of Arragon reasons his way through the caskets. The lead is too plain, he suspects, and the gold too ostentatious; the "many" people who value appearances over reality would choose it but would be mistaken to do so.
In considering the silver casket, Arragon considers carefully, reflecting that many who are rich and powerful do not deserve to be so, while many who are poor and weak deserve more wealth and power than they can claim. After much reflection, Arragon decides he does, in fact, deserve Portia, saying:
"'Who chooseth me shall get as much as he deserves.'
I will assume desert. Give me a key for this,
And instantly unlock my fortunes here" (2.9.48-50).
Unfortunately, he unlocks a puppet instead, informing him that he has chosen incorrectly.