It is strange that a notion so abstract as that of perfection, or a certain ideal completeness of nature, should ever have been thought one from which a system of guidance can be evolved; as it was in a general way by Plato and more distinctly by Jonathan Edwardes. Perfection is synonymous with goodness in the highest degree; and hence to define good conduct in terms of perfection, is indirectly to define good conduct in terms of itself. Naturally, therefore, it happens that the notion of perfection like the notion of goodness can be framed only in relation to ends. (§12 ¶1)

We allege imperfection of any inanimate thing, as a tool, if it lacks some part needful for effectual action, or if some part is so shaped as not to fulfil its purpose in the best manner. Perfection is alleged of a watch if it keeps exact time, however plain its case; and imperfection is alleged of it because of inaccurate time-keeping, however beautifully it is ornamented. Though we call things imperfect if we detect in them any injuries or flaws, even when these do not detract from efficiency; yet we do this because they imply that inferior workmanship, or that wear and tear, with which inefficiency is commonly joined in experience: absence of minor imperfections being habitually associated with absence of major imperfections. (§12 ¶2)

As applied to living things, the word perfection has the same meaning. The idea of perfect shape in a race-horse is derived by generalization from those observed traits of racehorses which have usually gone along with attainment of the highest speed; and the idea of perfect constitution in a race-horse similarily refers to the endurance which enables him to continue that speed for the longest time. With men, physically considered, it is the same: we are able to furnish no other test of perfection, than that of complete power in all the organs to fulfil their respective functions. That our conception of perfect balance among the internal parts, and of perfect proportion among the external parts, originates thus, is made clear by observing that imperfection of any viscus, as lungs, heart, or liver, is ascribed for no other reason than inability to meet in full the demands which the activities of the organism make on it; and on observing that the conception of insufficient size, or of too great size, in a limb, is derived from accumulated experiences respecting that ratio among the limbs which furthers in the highest degree the performance of all needful actions. (§12 ¶3)

And of perfection in mental nature we have no other measure. If imperfection of memory, of judgment, of temper, is alleged, it is alleged because of inadequacy to the requirements of life; and to imagine a perfect balance of the intellectual powers and of the emotions, is to imagine that proportion among them which ensures an entire discharge of each and every obligation as the occasion calls for it. (§12 ¶4)

So that the perfection of man considered as an agent, means the being constituted for effecting complete adjustment of acts to ends of every kind. And since, as shown above, the complete adjustment of acts to ends is that which both secures and constitutes the life that is most evolved, alike in breadth and length; while, as also shown, the justification for whatever increases life is the reception from life of mere happiness than misery; it follows that conduciveness to happiness is the ultimate test of perfection in a man’s nature. To be fully convinced of this it needs but to observe how the proposition looks when inverted. It needs but to suppose that every approach towards perfection involved greater misery to self, or others, or both, to show by opposition that approach to perfection really means approach to that which secures greater happiness. (§12 ¶5)