Institutio Oratoria

Moreover every law either gives or takes away punishes or commands, forbids or permits, and involves a dispute either on its own account or on account of another law, while the question which it involves will turn either on the letter or the intention. The letter is either clear or obscure or ambiguous.

And what I say with reference to laws will apply equally to wills, agreements, contracts and every form of document; nay, it will apply even to verbal agreements. And since I have classified such cases under four questions or bases, I will deal with each in turn.