A little over a century ago, De Tocqueville ended the first volume of Democracy in America with the flashing paragraph which identified two rising nations destined to become transcendent centers of power. The prescience of that ending was matched by the closing sentence of the second volume: “The nations of our time cannot prevent the conditions of men from becoming equal, but it depends upon themselves whether the principle of equality is to lead them to servitude or freedom, to knowledge or barbarism, to prosperity or wretchedness.” This sentence is more than a frame of the age, even to the hour. It hints at a theory of history; it is a clue to the relation of trends and choices.

Each major trend, holding such momentous alternatives, is itself the cumulative outcome of choices. The main alternatives, likewise, result from the interaction of fresh ideas with tradition, available resources, and potential techniques. Each new choice sets in motion its limited train of consequences, to be worked out in a succession of adaptive changes. In this restricted sense, man is intermittently the captive of his own discoveries. But spontaneity survives amid the accommodating changes launched by earlier acts of creation. Recurrently, as well as originally and fundamentally, ideas are the determinants.