The History of Western Philosophy by Bertrand Russell

Humanity left childhood and entered the troubled but productive world when it started to criticize its own certainties and weigh the worthiness of its most secure beliefs. Thus began that "Long Debate" on the nature of truth, the scale of real values, the life one should aspire to live, the character of justice, the sources of law, the terms of civic and political life—the good, the better, the best.