Goodness and Being are the same in substance but different according to our mode of conception; for Goodness implies the notion of desirability, whereas Being is necessarily not bound up with anything of that kind. Nevertheless, as everything is good and perfect according to its actuality, a thing is good in proportion to its measure of being, which is actuality, and hence Goodness and Being are substantially the same. Being, however, is prior to Goodness in our conception of them, because a thing is knowable accordingly as it is actual; and, therefore, since Being is the proper object of the intellect, it falls under knowledge, and is thus prior to Goodness.
Every being, as such, is good, for being is actuality, which is a perfection, and this again is desirable and good in our idea of it, and hence everything is good; and good is a final cause because it is desirable. What is desirable is a final cause for the reason because that which is first in the cause itself comes last in the thing which is caused; thus fire gives heat before it produces the nature of fire in its effect, although heat in the fire produces the substantial form. Hence in the process of causation we find, first, good, and the end which moves the efficient cause; secondly, the act of the efficient cause to the form; thirdly, there comes the form; and hence the contrary must be the case in the effect caused; for first is the form which makes it a being; secondly, the effective power which makes it perfect in being, because each thing is perfect accordingly as it can produce its likeness; thirdly, comes the idea of goodness which makes a thing perfect.
The idea of Good is expressed in Mode, Species, and Order. The form makes everything what it is, and this presupposes antecedent and consequent principles, as, for instance, determination to one form or commensuration of its principles, whether material or efficient; and this is signified by mode; hence it is said that measure fixes the mode. The species is signified in the form because each thing is constituted in a species by the form, and tendency to the end or to action follows from the form. Further, each thing acts so far as it is in actuality and tends to that which belongs to it according to its form; and this belongs to order. Hence the idea of Good implying perfection consists in mode, species, and order. So Good is properly divided -into the useful, the just and the delectable. That which is desirable and terminates the movement of desire as the means whereby it tends to something else, is called useful; that which is desired as an end so as to entirely terminate desire and is desired for its own sake, is called just; and that which, being desired for its own sake, terminates desire by rest in the desired thing, is called delectable. Good is thus properly divided into these three.
- text taken from Compendium of the Summa Theologica of Saint Thomas Aquinas, by Bishop Berardus Bongiovanni