I DO' (3 letters) The wedding ritual is a traditional ceremony that includes the exchange of vows and the phrase 'I DO'. VOW is a three letter word, and 'I DO' is also a three letter phrase. The exchange of vows is a common part of the wedding ritual, in which the couple promises to love and support each other for the rest of their lives. The phrase 'I DO' is then said by the couple to signify their commitment to each other.