153. The explanation of the cause of evil by a particular principle, _per principium maleficum_, is of the same nature. Evil needs no such explanation, any more than do cold and darkness: there is neither _primum frigidum_ nor principle of darkness. Evil itself comes only from privation; the positive enters therein only by concomitance, as the active enters by concomitance into cold. We see that water in freezing is capable of breaking a gun-barrel wherein it is confined; and yet cold is a certain privation of force, it only comes from the diminution of a movement which separates the particles of fluids. When this separating motion becomes weakened in the water by the cold, the particles of compressed air concealed in the water collect; and, becoming larger, they become more capable of acting outwards through their buoyancy. The resistance which the surfaces of the proportions of air meet in the water, and which opposes the force exerted by these portions towards dilation, is far less, and consequently the effect of the air greater, in large air-bubbles than in small, even though these small bubbles combined should form as great a mass as the large. For the resistances, that is, the surfaces, increase by the _square_, and the forces, that is, the contents or the volumes of the spheres of compressed air, increase by the _cube_, of their diameters. Thus it is _by accident_ that privation involves action and force. I have already shown how privation is enough to cause error and malice, and [220] how God is prompted to permit them, despite that there be no malignity in him. Evil comes from privation; the positive and action spring from it by accident, as force springs from cold. 154. The statement that M. Bayle attributes to the Paulicians, p. 2323, is not conclusive, to wit, that free will must come from two principles, to the end that it may have power to turn towards good and towards evil: for, being simple in itself, it should rather have come from a neutral principle if this argument held good. But free will tends towards good, and if it meets with evil it is by accident, for the reason that this evil is concealed beneath the good, and masked, as it were. These words which Ovid ascribes to Medea, _Video meliora proboque,_ _Deteriora sequor_, imply that the morally good is mastered by the agreeably good, which makes more impression on souls when they are disturbed by the passions.