This article seeks to clarify the meaning of conscience and to exhibit its role in the philosophy of Hobbes. The author compares Hobbes's philosophy to Locke's doctrine. Instead of the usual contrast of Hobbes, the enemy to the claims of conscience, and Locke, the defender of the rights of conscience, he shows that Hobbes found a place for conscience within the law—the rights of defendants to a jury of their choice, and the rights of jurors to a verdict according to their conscience—whereas Locke found a place for conscience outside the law, in the judgment of revolutionaries when a revolution is justifiable or successful. In elaborating Hobbes's views of trial by jury, the author suggests that the best forensic metaphor for conscience is a juror (rather than the more usual ones of a witness, a judge or a legislator). Conscience is subjective certainty, dangerous outside an institutional setting, but indispensable for decisions not based on demonstrable knowledge, such as a juror's verdict beyond reasonable doubt.