A slippery slope

"There is an infinite distance between God’s prohibition of murder and your speculative permission of the crime; but between that [speculative] permission and the practice the distance is very small indeed. . . . .  what is allowable in speculation is also so in practice. . . . .  Such is the wonderful growth attained by the doctrine of probability in general, as well as by every probable opinion in particular, in the course of time.  Attend . . . to what [the Jesuit Escobar] says [(i.e. came eventually openly to admit)]:  'I cannot see how it can be that an action which seems allowable in speculation should not be so likewise in practice; because what may be done in practice depends on what is found to be lawful in speculation, and the things differ from each other only as cause and effect.  Speculation is that which determines to action.  Whence it follows that opinions probable in speculation may be followed with a safe conscience in practice. . . .'
     "Verily, fathers, your friend Escobar reasons uncommonly well sometimes; and, in point of fact, there is such a close connection between speculation and practice, that when the former has once taken root, you have no difficulty in permitting the latter, without any [further] disguise."

     Blaise Pascal, Provincial letters no. 13, trans. M’Crie (GBWW, 1st ed. (1952), vol. 33, p. 103) =pp. 31-32 in tom. 6 of the 1904-1914 critical edition of the Œuvres edited by Brunschvicg, and pp. 728-729 in tom. 1 of the 1998 Pleiade edition of the Œuvres edited by Le Guern.