What reason does Antonio give for being sad in the opening scene of the play?

Literal-comprehension questions test whether a reader can separate what a character explicitly states about themselves from what other characters merely speculate or suggest on their behalf; the correct reading follows only the character's own confirmed words, not a bystander's guess.

In the opening scene of The Merchant of Venice, Antonio begins by declaring, "In sooth, I know not why I am so sad" — a plain admission that he cannot account for his own mood. Salarino and Solanio in turn guess that his ventures at sea are the cause, but Antonio answers that his fortune is not risked in any single voyage, ruling that out himself. Solanio then wonders whether he must be in love, and Antonio brushes the idea off with a curt "Fie, fie!" — no confirmation at all. The scene closes with his melancholy unexplained: every proposed cause comes from someone else and is either denied or waved aside, so the only reading the text supports is that Antonio never actually gives a reason.

Checking each proposed cause against Antonio's own words:

• his ventures at sea — raised by Salarino and Solanio, but Antonio himself denies that his fortune rests on any one voyage, so this cannot be his own stated cause.

• the sum owed to Shylock — this debt is arranged only in a later scene, once Bassanio asks Antonio to fund his courtship of Portia and the two of them approach Shylock for the loan; it does not exist yet at the moment Antonio is asked why he is sad.

• a woman who does not return his feelings — this echoes Solanio's guess that Antonio must be in love, a guess Antonio waves off with "Fie, fie!" rather than confirms.

Since every candidate cause is either raised by someone else and rejected, or belongs to a later part of the plot, the opening exchange supports only one reading: Antonio openly admits he does not know why he is sad.