The canonical answer to a question is a declarative sentence which provides the bit of information left open in the question. Thus:

• The canonical answer to a polar interrogative sentence is a declarative sentence reproducing its proposition in positive or negative form, reducible to ‘yes’ or ‘no’.
• The canonical answer to a content interrogative is a declarative sentence which contains, instead of the interrogative proform, an expression providing more information than that proform, reducible to this expression.