Ver. 31. Superior beings, &c.] To give this second argument its full force, he illustrates it, from ver. 30 to 43, by the noblest example that ever was in science, the incomparable Newton, who, although he penetrated so far beyond others into the works of God, yet could go no further in the knowledge of his own nature than the generality of his fellows. Of which the poet assigns this very just and adequate reason,—in all other sciences the understanding is unchecked and uncontrolled by any opposite principle; but in the science of man, the passions overturn as fast as reason can build up.
Ver. 43. Trace science then, &c.] The conclusion, therefore, from the whole is, from ver. 42 to 53, that as on the one hand, we should persist in the study of nature, so, on the other, in order to arrive at science, we should proceed in the simplicity of truth; and then the produce, though small, will yet be real.
Ver. 53. Two principles, &c.] The poet having shown the difficulty which attends the study of man, proceeds to remove it, by laying before us the elements or true principles of this science, in an account of the origin, use, and end of the passions; which, in my opinion, contains the truest, clearest, shortest, and consequently the best system of ethics that is anywhere to be met with. He begins, from ver. 52 to 59, with pointing out the two grand principles in human nature, self-love and reason. Describes their general nature: the first sets man upon acting, the other regulates his action. However, these principles are natural, not moral; and, therefore, in themselves, neither good nor evil, but so only as they are directed. This observation is made with great judgment, in opposition to the desperate folly of those fanatics, who, as the ascetic, vainly pretend to eradicate self-love; or, as the mystic, are more successful in stifling reason; and both, on the absurd fancy of their being moral, not natural, principles.
Ver. 59. Self-love, the spring of motion, acts the soul;] The poet proceeds, from ver. 58 to 67, more minutely to mark out the distinct offices of these two principles, which offices he had before assigned only in general; and here he shows their necessity; for without self-love, as the spring, man would be unactive; and without reason as the balance, active to no purpose.
Ver. 67. Most strength the moving principle requires:] Having thus explained the ends and offices of each principle, he goes on, from ver. 66 to 79, to speak of their qualities; and shows how they are fitted to discharge those functions, and answer their respective intentions. The business of self-love being to excite to action, it is quick and impetuous; and moving instinctively, has, like attraction, its force prodigiously increased as the object approaches, and proportionably lessened as it recedes. On the contrary, reason, like the Author of attraction, is always calm and sedate, and equally preserves itself whether the object be near or far off. Hence the moving principle is made more strong, though the restraining be more quick-sighted. The consequence he draws from this is, that if we would not be carried away to our destruction, we must always keep reason upon guard.
Ver. 79. Attention, &c.] But it would be objected, that if this account be true, human life would be most miserable; and even in the wisest, a perpetual conflict between reason and the passions. To this, therefore, the poet replies, from ver. 78 to 81, first, that Providence has so graciously contrived, that even in the voluntary exercise of reason, as in the mechanic motion of a limb, habit makes what was at first done with pain, easy and natural. And secondly, that the experience gained by the long exercise of reason, goes a great way towards eluding the force of self-love. Now the attending to reason, as here recommended, will gain us this habit and experience. Hence it appears, that our station, in which reason is to be kept constantly upon guard, is not so uneasy a one as may be at first imagined.
Ver. 81. Let subtle schoolmen, &c.] From this description of self-love and reason, it follows, as the poet observes, from ver. 80 to 93, that both conspire to one end, namely, human happiness, though they be not equally expert in the choice of the means; the difference being this, that the first hastily seizes every thing which has the appearance of good; the other weighs and examines whether it be indeed what it appears. This shows, as he next observes, the folly of the schoolmen, who consider them as two opposite principles, the one good and the other evil. The observation is seasonable and judicious; for this dangerous school-opinion gives great support to the Manichean or Zoroastrian error, the confutation of which was one of the author's chief ends in writing. For if there be two principles in man, a good and evil, it is natural to think him the joint product of the two Manichean Deities (the first of which contributed to his reason, the other to his passions), rather than the creature of one Individual Cause. This was Plutarch's opinion, and as we may see in him, of some of the more ancient theistical philosophers. It was of importance, therefore, to reprobate and subvert a notion that served to the support of so dangerous an error; and this the poet hath done with more force and clearness than is often to be found in whole volumes written against that heretical opinion.
Ver. 93. Modes of self-love, &c.] Having given this account of the nature of self-love in general, he comes now to anatomize it, in a discourse on the passions, which he aptly names the modes of self-love. The object of all these, he shows, from ver. 92 to 101, is good; and when under the guidance of reason, real good, either of ourselves or of another; for some goods, not being capable of division, or communication, and reason at the same time directing us to provide for ourselves, we therefore, in pursuit of these objects, sometimes aim at our own good, sometimes at the good of others. When fairly aiming at our own, the quality is called prudence; when at another's, virtue. Hence as he shows, from ver. 100 to 105, appears the folly of the stoics, who would eradicate the passions, things so necessary both to the good of the individual and of the kind. Which preposterous method of promoting virtue he therefore very reasonably reproves.
Ver. 105. The rising tempest puts in act the soul,] But as it was from observation of the evils occasioned by the passions, that the stoics thus extravagantly projected their extirpation, the poet recurs, from ver. 104 to 111, to his grand principle, so often before, and to so good purpose, insisted on, that partial ill is universal good; and shows, that though the tempest of the passions, like that of the air, may tear and ravage some few parts of nature in its passage, yet the salutary agitation produced by it preserves the whole in life and vigour. This is his first argument against the stoics, which he illustrates by a very beautiful similitude, on a hint taken from Scripture:
Nor God alone in the still calm we find;
He mounts the storm, and walks upon the wind.