Zero Anaphora Resolution (or Zero Pronoun Resolution) is the task of identifying and resolving "empty" or "dropped" pronouns that are grammatically omitted but semantically implied — a major challenge in pro-drop languages like Chinese, Japanese, and Italian.

The Phenomenon

• English: "I went to the store. I bought milk." (Explicit).
• Japanese: "Store went. Milk bought." (Implicit/Zero Subject).
• Task: The model must realize "Milk bought" implies "[I] bought milk" based on context.

Why It Matters

• Translation: Translating Japanese to English REQUIRES restoring these dropped pronouns, otherwise output is broken grammar ("Bought milk.").
• Ambiguity: "Saw context." -> Did I see it? Did He see it? The model must infer the hidden subject.
• Difficulty: Much harder than standard coreference because there is no span to link — you must link to a "void".

Zero Anaphora Resolution is finding the ghosts — detecting and resolving the invisible pronouns that fluent speakers omit.