Marriage is intended to establish a lawful marital relationship. Where the woman herself is legally ineligible for marriage to the person concerned, it is not enough to say that marriage as a category is generally recognized.
Marriage to a prohibited relative: the prohibition conflicts with the very licit relationship the contract would establish; it cannot simply be analogized to a defective sale.
Marriage without witnesses: this involves separate conditions and legal consequences. It should not be treated as identical to a marriage with a prohibited partner. The subject, contract conditions, and consequences require distinct examination.