%A Michel Cabanac %A Remi A. Cabanac %A Harold T. Hammel %T The Fifth Influence %X This article is a theoretical consideration on the role of sensory pleasure and mental joy as optimizers of behavior. It ends with an axiomatic proposal. When they compare the human body to its environment, Philosophers recognise the cosmos as the Large Infinite, and the atomic particles as the Small Infinite. The human brain reaches such a degree of complexity that it may be considered as a third infinite in the universe, a Complex Infinite. It follows that any force capable of moving such an infinite deserves a place among the forces of the universe. Physicists have recognized four forces, the gravitational, the electromagnetic, the weak, and the strong nuclear force. Forces are defined in four dimentions (reversible or not in time) and it is postulated that these forces are valid and applicable everywhere. Pleasure and displeasure, the affective axis of consciousness, can move the infinitely complex into action and no human brain can avoid the trend to maximize its pleasure. Therefore, we suggest, axiomatically, that the affective capability of consciousness operates in a way similar to the four forces of the Physics, i.e. influences the behavior of conscious agents in a way similar to the way the four forces influence masses and particles. However, since a mental phenomenon is dimensioneless we propose to call the affective capability of consciousness the fifth influence rather than the fifth force. %D 1999 %I ISSS, CD-ROM %P 1-10 %L cogprints183