# Treatise of Human Nature/Book 2: Of the passions/Part 3/Section 4

SECTION IV.
Of the causes of the violent passions.
There is not in philosophy a subject of more nice speculation than this of the different causes and effects of the calm and violent passions. 'Tis evident passions influence not the will in proportion to their violence, or the disorder they occasion in the temper; but on the contrary, that when a ​passion has once become a settled principle of action, and is the predominant inclination of the soul, it commonly produces no longer any sensible agitation. As repeated custom and its own force have made every thing yield to it, it directs the actions and conduct without that opposition and emotion, which so naturally attend every momentary gust of passion. We must, therefore, distinguish betwixt a calm and a weak passion; betwixt a violent and a strong one. But notwithstanding this, 'tis certain, that when we wou'd govern a man, and push him to any action, 'twill commonly be better policy to work upon the violent than the calm passions, and rather take him by his inclination, than what is vulgarly call'd his reason. We ought to place the object in such particular situations as are proper to encrease the violence of the passion. For we may observe, that all depends upon the situation of the object, and that a variation in this particular will be able to change the calm and the violent passions into each other. Both these kinds of passions pursue good, and avoid evil; and both of them are encreas'd or diminish'd by the encrease or diminution of the good or evil. But herein lies the difference betwixt them: The same good, when near, will cause a violent passion, which, when remote, produces only a calm one. As this subject belongs very properly to the present question conceding the will, we shall here examine it to the bottom, and shall consider some of those circumstances and situations of objects, which render a passion either calm or violent.
'Tis a remarkable property of human nature, that any emotion, which attends a passion, is easily converted into it, tho' in their natures they be originally different from, and even contrary to each other. 'Tis true; in order to make a perfect union among passions, there is always requir'd a double relation of impressions and ideas; nor is one relation sufficient for that purpose. But tho' this be confirm'd by undoubted experience, we must understand it with its proper limitations, and must regard the double ​relation, as requisite only to make one passion produce another. When two passions are already produc'd by their separate causes, and are both present in the mind, they readily mingle and unite, tho' they have but one relation, and sometimes without any. The predominant passion swallows up the inferior, and converts it into itself. The spirits, when once excited, easily receive a change in their direction; and 'tis natural to imagine this change will come from the prevailing affection. The connexion is in many respects closer betwixt any two passions, than betwixt any passion and indifference.
When a person is once heartily in love, the little faults and caprice of his mistress, the jealousies and quarrels, to which that commerce is so subject; however unpleasant and related to anger and hatred; are yet found to give additional force to the prevailing passion. 'Tis a common artifice of politicians, when they wou'd affect any person very much by a matter of fact, of which they intend to inform him, first to excite his curiosity; delay as long as possible the satisfying it; and by that means raise his anxiety and impatience to the utmost, before they give him a full insight into the business. They know that his curiosity will precipitate him into the passion they design to raise, and assist the object in its influence on the mind. A soldier advancing to the battle, is naturally inspir'd with courage and confidence, when he thinks on his friends and fellow-soldiers; and is struck with fear and terror, when he reflects on the enemy. Whatever new emotion, therefore, proceeds from the former naturally encreases the courage; as the same emotion, proceeding from the latter, augments the fear; by the relation of ideas, and the conversion of the inferior emotion into the predominant. Hence it is that in martial discipline, the uniformity and lustre of our habit, the regularity of our figures and motions, with all the pomp and majesty of war, encourage ourselves and allies; while the same objects in the enemy strike terror into us, tho' agreeable and beautiful in themselves.
​Since passions, however independent, are naturally transfus'd into each other, if they are both present at the same time; it follows, that when good or evil is plac'd in such a situation, as to cause any particular emotion, beside its direct passion of desire or aversion, that latter passion must acquire new force and violence.
This happens, among other cases, whenever any object excites contrary passions. For 'tis observable that an opposition of passions commonly causes a new emotion in the spirits, and produces more disorder, than the concurrence of any two affections of equal force. This new emotion is easily converted into the predominant passion, and en creases its violence, beyond the pitch it wou'd have arriv'd at had it met with no opposition. Hence we naturally desire what is forbid, and take a pleasure in performing actions, merely because they are unlawful. The notion of duty, when opposite to the passions, is seldom able to overcome them; and when it fails of that effect, is apt rather to encrease them, by producing an opposition in our motives and principles.
The same effect follows whether the opposition arises from internal motives or external obstacles. The passion commonly acquires new force and violence in both cases. The efforts, which the mind makes to surmount the obstacle, excite the spirits and inliven the passion.
Uncertainty has the same influence as opposition. The agitation of the thought; the quick turns it makes from one view to another; the variety of passions, which succeed each other, according to the different views: All these produce an agitation in the mind, and transfuse themselves into the predominant passion.
There is not in my opinion any other natural cause, why security diminishes the passions, than because it removes that uncertainty, which encreases them. The mind, when left to itself, immediately languishes; and in order to preserve its ardour, must be every moment supported by a new flow of ​ passion. For the same reason, despair, tho' contrary to security, has a like influence.
'Tis certain nothing more powerfully animates any affection, than to conceal some part of its object by throwing it into a kind of shade, which at the same time that it shews enough to pre-possess us in favour of the object, leaves still some work for the imagination. Besides that obscurity is always attended with a kind of uncertainty; the effort, which the fancy makes to compleat the idea, rouzes the spirits, and gives an additional force to the passion.
As despair and security, tho' contrary to each other, produce the same effects; so absence is observ'd to have contrary effects, and in different circumstances either encreases or diminishes our affections. The Duc de la Rochefoucault has very well observ'd, that absence destroys weak passions, but encreases strong; as the wind extinguishes a candle, but blows up a fire. Long absence naturally weakens our idea, and diminishes the passion: But where the idea is so strong and lively as to support itself, the uneasiness, arising from absence, encreases the passion, and gives it new force and violence.