Learn Italian: Se solo una sua carezza potesse cancellare tutta questa amarezza! - If only a caress of his could erase all this bitterness!

The phrase se solo (if only) expresses a strong, often unrealizable wish. When referring to a present or future wish, it triggers the imperfect subjunctive, like potesse. If it were a regret about the past, we would use the pluperfect subjunctive, such as se solo avesse potuto (if only he had been able to).

Why does the sentence use una sua carezza instead of la sua carezza?

Combining the indefinite article una with the possessive sua means a caress of his or one of his caresses. If it were la sua carezza, it would mean his caress, pointing to a single, specific one rather than any general caress from him.

Since carezza is feminine, does sua mean the person giving the caress is a woman?

Not necessarily! The possessive adjective sua takes its feminine ending to agree with the noun it modifies (carezza), regardless of the gender of the person it belongs to. Grammatically, it could mean a caress of his, hers, or yours in the formal address. The context of the story provides the translation his.

I learned that tutto is usually followed by a definite article. Why is there no article in tutta questa amarezza?