You can create favorable circumstances for a person to do something but cannot force him or her to do it. This metaphor was already being used in the twelfth century, when horses were a principal mode of transport, and appeared in John Heywood’s proverb collection of 1546. Several eighteenth- and nineteenth-century writers rang changes on it, mainly by increasing the second “you” to a large number. Samuel Johnson wrote “twenty cannot make him drink” (1763); Anthony Trollope made it “a thousand” (1857). In the twentieth century, keen-witted Dorothy Parker, in a speech before the American Horticultural Society, quipped, “You can lead a whore to culture but you can’t make her think.”