Starting from the hedonistic doctrine of Epicurus, that puts (moderate) pleasure seeking and bodily and emotional pain avoidance as the bases of good life, the pleasure/pain dualism has always been a central theme in philosophical and then scientific thought. In the classical utilitarian theory of Bentham, where pleasure and pain are explicitly said to be the governors of human thoughts and actions, the utility of somethi ng is measured by the happiness or pleasure it produces and the unhappiness or pain it avoids.