1 Commentary on Luke, Book IV, chap. 5. Patrologia Latina, 15, col. 1693.

Chapter 1

Why Are There Three Partsof the Summa?

Saint Thomass Introduction (ST, I, 1, 1)In order to establish a scientific procedure for theology, SaintThomas was always careful to proceed from the more to theless common, from causes to the caused, and from the moreknown to the less known. Therefore, in the very first andintroductory question, he considers the science itself, explain-ing its necessity, dignity, specification, and mode of proceed-ing. Second, he considers the object of this science, discussingthe various matters with which the science is concerned andthe order among them, an order needed just because they arevarious and diverse. As for the formal object, no ordering isneeded, since it is one. The formal object of any science is thatwhich orders, not that which is ordered. But it was necessaryfor him first to treat the science itself and then its object, sincebeginners in any science must first be taught the usefulnessand worth of that science before disputes about particularmatters can be treated.

Division of the Material Object of TheologyHaving discussed in the prefatory question the science

itself of theology, Thomas sets out to plumb the depths of theobject to be explained. This is to set out upon the deep, asAmbrose explains1 when discussing Christs words to Peter,

10 Book One: The Three Parts of the Summa and Their Treatises

2 Second Prayer for Easter. Patrologia Latina, 36, col. 626.3 Prologue to the Exposition of Boethiuss On the Trinity.

Put out into the deep, and lower your nets for a catch.(Luke 5, 4) The object of theology is profoundly deep, for it isGod himself, God as God, in all the fullness of his being, thatis, not just this or that attribute, for example, wisdom or jus-tice, but the very essence and formality of deity along with allhis attributes, for God is an infinite ocean of being, as SaintGregory of Nazianzus put it.2

Given an object so deep and profound, Thomas firstdivides it into two aspects: its being and its causality, and fit-tingly enough, since activity follows on being. As SaintThomas remarks elsewhere:3 Although knowledge of thecreated effects of God comes before knowledge of God for thenatural theologian, for the theologian, consideration of theCreator takes precedence over the consideration of crea-tures. Although the principal theological concern is Godsbeing, the theologian spends more time discussing God ascausing and the things caused by him, since in this life weknow God through the mirror of creatures and the darknessof his effects.

The treatment of God as causing, as the cause of creatures,fittingly excludes two of the four kinds of cause, namely,material and formal (in the sense of informing and constitut-ing a nature). The material cause is excluded because it isbased on potentiality, which is repugnant to the pure act Godis; the formal or informing cause is excluded because itimplies dependence and inferiority, either to the whole it con-stitutes (the whole is greater than its part) or to the subject inwhich it inheres. Since God is the most perfect being, andpure act, he is inferior to nothing, nor does he depend on any-thing. As for the other two causes, namely, the efficient andfinal, Saint Thomas considers three modes of causing whichprovide a division of the whole theological order.

First, God is an efficient cause, insofar as he produces,conserves, and governs things.

Second, God as final cause, not just the universal end of

CHAPTER 1: WHY ARE THERE THREE PARTS OF THE SUMMA? 11

all creatures something Saint Thomas treats briefly when heconsiders the way things proceed from God (See First Part,q. 44) but much more importantly as he is the particular endof the rational creature, by whom he is attainable and forwhom he is an object of joy through acts of intellect and will.Thus it is that creatures not only proceed from God but returnto him from whom they have come. But the rational creaturefell from his proper dignity by sin and became like irrationalcreatures in not returning to God, stuck in the enjoyment ofcreated goods and turned away from God. Man living inwealth and not understanding, is like unto the beasts thatperish. (Psalm 48, 21)

That is why in a third way God causes and acts as repair-ing the effects of sin which turned man from his ultimate end,something only God can do. Just as to be separated from thefirst efficient cause is annihilation, which only God can pre-vent, who sustains all things by the word of his power, soto turn from the ultimate end, which is to sin, is somethingonly God, who cleanses us from our sins, can repair. Thesetwo are opportunely conjoined by the Apostle when he saysof the Son of God, by whom also he made the world; whobeing the brightness of his glory and the image of his sub-stance, and upholding all things by the word of his power,has effected mans purgation from sin . . . (Hebrews 1, 3) Hisefficient causality is signified by upholding all things andhis role as redeemer by has effected mans purgation fromsin.

So it is that Saint Thomas, by this threefold considerationof God as cause, namely as effective principle (Part One), asfinalizing happiness (Part Two), and as redeeming Savior(Part Three), divides the whole Summa theologiae. (This is clearfrom the second question of the First Part.) Thus from Godconsidered in himself and in his being, we pass to God as effi-cient and redemptive cause, in order to come back to him asthe object of happiness after the glorious resurrection. So it isthat the golden circle of theology is closed.