Objection 1. It seems that the essence of goodness does not consist in mode, species and order. For goodness and being differ logically. But mode, species and order seem to belong to the nature of being, for it is written: "Thou hast ordered all things in measure, and number, and weight" (Wisdom 11:21). And to these three can be reduced species, mode and order, as Augustine says (Gen. ad lit. iv, 3): "Measure fixes the mode of everything, number gives it its species, and weight gives it rest and stability." Therefore the essence of goodness does not consist in mode, species and order.
Objection 2. Further, mode, species and order are themselves good. Therefore if the essence of goodness consists in mode, species and order, then every mode must have its own mode, species and order. The same would be the case with species and order in endless succession.
Objection 3. Further, evil is the privation of mode, species and order. But evil is not the total absence of goodness. Therefore the essence of goodness does not consist in mode, species and order.
Objection 4. Further, that wherein consists the essence of goodness cannot be spoken of as evil. Yet we can speak of an evil mode, species and order. Therefore the essence of goodness does not consist in mode, species and order.
Objection 5. Further, mode, species and order are caused by weight, number and measure, as appears from the quotation from Augustine. But not every good thing has weight, number and measure; for Ambrose says (Hexam. i, 9): "It is of the nature of light not to have been created in number, weight and measure." Therefore the essence of goodness does not consist in mode, species and order.
On the contrary, Augustine says (De Nat. Boni. iii): "These three--mode, species and order--as common good things, are in everything God has made; thus, where these three abound the things are very good; where they are less, the things are less good; where they do not exist at all, there can be nothing good." But this would not be unless the essence of goodness consisted in them. Therefore the essence of goodness consists in mode, species and order.
I answer that, Everything is said to be good so far as it is perfect; for in that way only is it desirable (as shown above 1, 3). Now a thing is said to be perfect if it lacks nothing according to the mode of its perfection. But since everything is what it is by its form (and since the form presupposes certain things, and from the form certain things necessarily follow), in order for a thing to be perfect and good it must have a form, together with all that precedes and follows upon that form. Now the form presupposes determination or commensuration of its principles, whether material or efficient, and this is signified by the mode: hence it is said that the measure marks the mode. But the form itself is signified by the species; for everything is placed in its species by its form. Hence the number is said to give the species, for definitions signifying species are like numbers, according to the Philosopher (Metaph. x); for as a unit added to, or taken from a number, changes its species, so a difference added to, or taken from a definition, changes its species. Further, upon the form follows an inclination to the end, or to an action, or something of the sort; for everything, in so far as it is in act, acts and tends towards that which is in accordance with its form; and this belongs to weight and order. Hence the essence of goodness, so far as it consists in perfection, consists also in mode, species and order.
Reply to Objection 1. These three only follow upon being, so far as it is perfect, and according to this perfection is it good.
Reply to Objection 2. Mode, species and order are said to be good, and to be beings, not as though they themselves were subsistences, but because it is through them that other things are both beings and good. Hence they have no need of other things whereby they are good: for they are spoken of as good, not as though formally constituted so by something else, but as formally constituting others good: thus whiteness is not said to be a being as though it were by anything else; but because, by it, something else has accidental being, as an object that is white.
Reply to Objection 3. Every being is due to some form. Hence, according to every being of a thing is its mode, species, order. Thus, a man has a mode, species and order as he is white, virtuous, learned and so on; according to everything predicated of him. But evil deprives a thing of some sort of being, as blindness deprives us of that being which is sight; yet it does not destroy every mode, species and order, but only such as follow upon the being of sight.
Reply to Objection 4. Augustine says (De Nat. Boni. xxiii), "Every mode, as mode, is good" (and the same can be said of species and order). "But an evil mode, species and order are so called as being less than they ought to be, or as not belonging to that which they ought to belong. Therefore they are called evil, because they are out of place and incongruous."
Reply to Objection 5. The nature of light is spoken of as being without number, weight and measure, not absolutely, but in comparison with corporeal things, because the power of light extends to all corporeal things; inasmuch as it is an active quality of the first body that causes change, i.e. the heavens.
Source: Summa Theologica (New Advent)