The conception of God and nature and of the relation of man to both provided the 18th- century philosophers with their faith in the worth and dignity of the individual man and the efficacy of human reason. The 18th century was the moment in history when men experienced the first flush and freshness of the idea that man is master of his own fate the moment in history, also, when this emancipating idea, not yet brought to the harsh test of experience, could be accepted with unclouded optimism. Never had the nature seemed less mysterious, more simply constructed, more open and visible and eager to yield its secrets to common-sense questions. Never had the nature of man seemed less perverse, or the intelligence and will of men more pliable (yielding) to rational persuasion. Never had social and political evils seemed so wholly the result of ignorance and superstition, or so easily corrected by the spread of knowledge and the construction of social institutions on a rational plan. The first task of political science was to discover the natural rights of man, the second to devise the form. of government best suited to secure them. And for accomplishing this high task, for creating and maintaining a society founded on justice and equality, the essential freedom was freedom of the mind. The initial words of this passage, 'the conception of God and nature', refer certainly to ______ .