It is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence. - W. K. Clifford - this forthright assertion of mathematician and educator W. K. Clifford (1845-1879) in his famous essay The Ethics of Belief drew an immediate response from Victorian-era critics, who took issue with his reasoned and brilliantly presented attack on beliefs not founded on fair inquiry . An advocate of evolutionary theory, Clifford recognised that working hypotheses and assumptions are necessary for belief formation and that testing and assessing one’s beliefs in light of new evidence strengthens those worthy of being held. The Ethics of Belief is presented here in complete form, along with an insightful biographical introduction by editor Timothy J. Madigan. Also included are four other noteworthy essays by Clifford: On the Aims and Instruments of Scientific Thought , Right and Wrong , The Ethics of Religion , and The Influence upon Morality of a Decline in Religious Belief .