... moral certainty is certainty which is sufficient to regulate our behaviour, or which measures up to the certainty we have on matters relating to the conduct of life which we never normally doubt, though we know that it is possible, absolutely speaking, that they may be false.
René Descartes (1596–1650), French philosopher, mathematician. A translation of the first sentence of the French version. Principles of Philosophy, pt. IV, sect. 205, from Selected Philosophical Writings, trans. by John Cottingham, et al..