“A promise is a commitment to do something later, and a vow is a binding commitment to begin doing something now and to continue to do it for the duration of the vow. Some vows, or contracts, are for life; others are for limited periods of time.”

Source: Pleasure of a Dark Prince

Source: Lady Midnight

Source: The Purpose and Power of Love & Marriage

Anastasia Steele, Chapter 4, p. 75.
Fifty Shades Freed (2011)

Hudibras, Part I (1663–1664)
Context: They'll say our bus'ness, to reform
The Church and State, is but a worm;
For to subscribe, unsight, unseen,
To an unknown Church-discipline,
What is it else, but before-hand
T'engage, and after understand?
For when we swore to carry on
The present Reformation,
According to the purest mode
Of Churches best reformed abroad,
What did we else, but make a vow
To do we know not what, nor how?

Source: As You Like It

Source: Romancing Mister Bridgerton