"Another finds himself forced by necessity to borrow money. He knows that he will not be able to
repay it, but sees also that nothing will be lent to him unless he promises stoutly to repay it in a
definite time. He desires to make this promise, but he has still so much conscience as to ask
himself: 'Is it not unlawful and inconsistent with duty to get out of a difficulty in this way?' Suppose
however that he resolves to do so: then the maxim of his action would be expressed thus: 'When I
think myself in want of money, I will borrow money and promise to repay it, although I know that I
never can do so.' Now this principle of self-love or of one's own advantage may perhaps be
consistent with my whole future welfare; but the question now is, 'Is it right?' I change then the
suggestion of self-love into a universal law, and state the question thus: 'How would it be if my
maxim were a universal law?' Then I see at once that it could never hold as a universal law of
nature, but would necessarily contradict itself. For supposing it to be a universal law that everyone
when he thinks himself in a difficulty should be able to promise whatever he pleases, with the
purpose of not keeping his promise, the promise itself would become impossible, as well as the
end that one might have in view in it, since no one would consider that anything was promised to
him, but would ridicule all such statements as vain pretences."
(Quoted from the Fundamental Principles of the Metaphysic of Morals,
as translated by T.K. Abbott)