Again you have heard that it was said to the men of old, "You shall not swear falsely, but shall perform to the Lord what you have sworn." But I say to you, do not swear at all, either by Heaven, for it is the throne of God, nor by the Earth, for it is His footstool, or by Jerusalem, for it is the city of the Great King. And do not swear by your head, for you cannot make one hair white or black. Let what you say be "Yes," or "No;" anything more than this comes from evil.
This one should be familiar for Quakers. (And I'm not at all sure that "I affirm because I'm a Quaker!" is any better; doesn't this come down to implying "You can believe me because I'm a religious person," pretty similar in fact to what an oath is supposed to mean?)
Is there an inconsistency in this, so far as getting married? Can anyone promise such a thing? -- Or do we simply find that there's no conflict over which we'd be willing to lose this person? Should we really understand those vows to mean, "This is what we intend, and hope for!"