Whatever be the reason for which a brain in love bends its love companion with a larger power of influence, the tyrant, too, undergoes the influence of the victim. Two thoughts cannot impunely be enclosed in the same atmosphere, they cannot follow the orbit of the same planetary system. The one gives much, and the other gives little; the one receives more than it gives, the other gives more than it receives; but they both alter and exchange influences and energies. This is a consequence of the most elementary laws of physics: two loves and two brains are two systems of forces; and, however powerful one may be in comparison with the other, they both must undergo, in their contacts, a molecular modification of their movements. To the direct influence of love add the automatic power of imitation, the tyranny of habit, the epicurism of the compromise of ideas and of conscience, and many other minor causes, and you will see how inexorably thought must change when we think in two. Not all intellectual phenomena undergo the influence of love in equal measure, but those feel it most who by contacts and origins are nearer to the energies of sentiment or are interwoven with them, constituting binary bodies, composed of affection and thought. Religion and morality are more easily modified than esthetic tastes, and these change more frequently than philosophical theories or the method of study. There is a certain architecture in our brains that constitutes their framework and can be destroyed only by death or insanity. Against it love is powerless; furthermore, certain intellectual antitheses between a man and a woman are enough to render love impossible, even when the sympathy of forms and a certain community of affections violently rouse the sovereign of sentiments.