Certainty is not what it used to be. Our ancestors had the certainty of their gods, myths and rituals, then of one God, his purposes and the orderliness of all that he had created. The Enlightenment promised a world freed from the lore of the past by the power of human reason; the industrial age a world endlessly made better by the unstoppable force of Progress. Few such absolute certainties survive in the twenty-first century and yet, it seems, we cannot resist the urge to cling on to the old ones, or to fabricate new ones.Why is this so? Certainty, that thing of indefinite approximation pieces together answers from an original and sometimes startling mix of sources - ranging from religious and philosophical texts to memoir, fiction and popular science. We would live better with ourselves and with each other, it concludes, if more of us could learn to tolerate 'being in uncertainties'.