Put a philosopher in a cage of small bars of thin iron suspended at the top of the towers of Notre Dame de Paris, he will see for obvious reasons that it is impossible for him to fall, and yet (unless he is used to the roofer's trade) he will not be able to keep the vision of that height from frightening and and astonishing him....There are some who cannot even bear the thought of it. Set a plank between those two towers, of a size such as is needed for us to walk on it: there is no philosophical wisdom of such firmness as to give us the courage to walk on it as we would do if it was on the ground.
[Montaigne, Essays II, ch. 12 (Ariew and Grene trans. p. 155)]
Put the world's greatest philosopher on a plank hanging over a precipice, but wider than it needs to be. Although his reason will convince him of his safety, his imagination will prevail. Many could not bear the thought of it without getting pale and sweating.
[Pascal, Pensées, S78/L44 (Ariew, tr., p. 13)]
To illustrate this by a familiar instance, let us consider the case of a man, who, being hung out from a high tower in a cage of iron cannot forbear trembling, when he surveys the precipice below him, tho' he knows himself to be perfectly secure from falling, by his experience of the solidity of the iron, which supports him; and tho' the ideas of fall and descent, and harm and death, be deriv'd solely from custom and experience. The same custom goes beyond the instances, from which it is deriv'd, and to which it perfectly corresponds; and influences his ideas of such objects as are in some respect resembling, but fall not precisely under the same rule. The circumstances of depth and descent strike so strongly upon him, that their influence can-not be destroy'd by the contrary circumstances of support and solidity, which ought to give him a perfect security. His imagination runs away with its object, and excites a passion proportion'd to it. That passion returns back upon the imagination and inlivens the idea; which lively idea has a new influence on the passion, and in its turn augments its force and violence; and both his fancy and affections, thus mutually supporting each other, cause the whole to have a very great influence upon him.
[Hume, Treatise 1.3.13.10]
