This article will attempt to determine the formal object of Sacred Theology and to unify and order the seemingly disparate accounts of the same given by St. Thomas: the formal object is the light of divine revelation (ST Ia,q.1, a.3), God (ST Ia, q.1, a.7), and things that are immaterial in such a way as to never exist in matter (In Boetium De Trinitate, q.5, a.4).

In q.1, a.3 of the Summa Theologiae, the Angelic Doctor teaches that the unity of a habit (science, in this case) comes from the formal account of its object:

Est enim unitas potentiae et habitus consideranda secundum obiectum, non quidem materialiter, sed secundum rationem formalem obiecti, puta homo, asinus et lapis conveniunt in una formali ratione colorati, quod est obiectum visus.

He goes on to specify that the unity of sacred theology comes from the one formal object of things able to be revealed:

Quia igitur sacra Scriptura considerat aliqua secundum quod sunt divinitus revelata, secundum quod dictum est, omnia quaecumque sunt divinitus revelabilia, communicant in una ratione formali obiecti huius scientiae.

So far, so good. When discussing the subject of the science, however, although he uses the same language of formal object (in fact, he uses the very same example from sight), he names God, not revealable things, as the formal object:

Sic enim se habet subiectum ad scientiam, sicut obiectum ad potentiam vel habitum. Proprie autem illud assignatur obiectum alicuius potentiae vel habitus, sub cuius ratione omnia referuntur ad potentiam vel habitum, sicut homo et lapis referuntur ad visum inquantum sunt colorata, unde coloratum est proprium obiectum visus. Omnia autem pertractantur in sacra doctrina sub ratione dei, vel quia sunt ipse deus; vel quia habent ordinem ad deum, ut ad principium et finem. Unde sequitur quod deus vere sit subiectum huius scientiae.

Finally, in his commentary on Boetius' De Trinitate, (in which St. Thomas uses the formal object as a principle of division), he distinguishes the science of Theology generically from Physics and Mathematics by its remotion from matter and motion:

Quaedam vero speculabilia sunt, quae non dependent a materia secundum esse, quia sine materia esse possunt, sive numquam sint in materia, sicut deus et Angelus, sive in quibusdam sint in materia et in quibusdam non, ut substantia, qualitas, ens, potentia, actus, unum et multa et huiusmodi. De quibus omnibus est theologia, id est scientia divina…

He later distinguishes Sacred Theology from Metaphysics by further specifying the kinds of immateriality involved in each:

Sic ergo theologia sive scientia divina est duplex. Una, in qua considerantur res divinae non tamquam subiectum scientiae, sed tamquam principia subiecti, et talis est theologia, quam philosophi prosequuntur, quae alio nomine metaphysica dicitur. Alia vero, quae ipsas res divinas considerat propter se ipsas ut subiectum scientiae et haec est theologia, quae in sacra Scriptura traditur. Utraque autem est de his quae sunt separata a materia et motu secundum esse, sed diversimode, secundum quod dupliciter potest esse aliquid a materia et motu separatum secundum esse. Uno modo sic, quod de ratione ipsius rei, quae separata dicitur, sit quod nullo modo in materia et motu esse possit, sicut deus et Angeli dicuntur a materia et motu separati. Alio modo sic, quod non sit de ratione eius quod sit in materia et motu, sed possit esse sine materia et motu, quamvis quandoque inveniatur in materia et motu. Et sic ens et substantia et potentia et actus sunt separata a materia et motu, quia secundum esse a materia et motu non dependent, sicut mathematica dependebant, quae numquam nisi in materia esse possunt, quamvis sine materia sensibili possint intelligi. Theologia ergo philosophica determinat de separatis secundo modo sicut de subiectis, de separatis autem primo modo sicut de principiis subiecti. Theologia vero sacrae Scripturae tractat de separatis primo modo sicut de subiectis, quamvis in ea tractentur aliqua quae sunt in materia et motu, secundum quod requirit rerum divinarum manifestatio.

Note, however, that the account of the specific object of Sacred Theology in this text is not the light of divine revelation as it was in the Summa; instead, it is immateriality of the sort that cannot exist in matter. Notice, also, that in this text St. Thomas determines the subject of each species of theology: Sacred Theology studies the first principle in itself and principally, while Metaphysics studies the first principle only in relation to created being.

First, concerning the distinction of the subject and object of Sacred Theology presented in the Summa, it should be noted that the object of any habit can be said materially or formally. St. Thomas makes this distinction explicit in the quote from Ia q.1, a.3 given above. The material object is considered under an account that only accidentally relates the thing to the power. In the example given by St. Thomas, it is only accidental that what is seen is a man or a rock. The formal object, on the other hand, is exactly the reason why it is grasped by a certain power, as things are seen precisely because they are colored.

Given this distinction between formal and material objects, however, it still remains to see why St. Thomas gives different accounts of the "object" and "subject" of Sacred Theology, since both accounts seem to be aiming at the formal object. It must be said, then, that the formal object of a habit itself is two-fold. For one could say that things are visible because they are colored; but it is also true to say that they are visible because they are illuminated. The color is what we see, the terminus of our action of seeing; but the light is that in which we see, not accidentally. The habit of sight is only fully specified by saying that its formal object is illuminated color. Color is an example of what is called by the scholastic tradition the formale obiectum quod, while light exemplifies the formale obiectum quo, or sub quo.¹

By extension, the formal object of sciences will also be two-fold. The formal object quo of a science is the light, so to speak, in which the science views its object quod. The light proper to science is immateriality, which is why St. Thomas divides the sciences in his commentary on Boetius' De Trinitate according to different degrees of remotion from matter and motion. This light determines a principle subject, or object quod, about which the science treats, and to which all other things treated by the science are referred, whether it be mobile being in Physics, for example, or quantity in Mathematics. For, given a certain mode of understanding, there will be a corresponding grade of being whose mode of existence is properly the cause of why the intellect can consider things under that light.

Therefore, when St. Thomas gives the principle of unity of Sacred Theology in Ia q.1, a.3, he is giving the obiectum quo. For Sacred Theology studies everything in the light of Divine Revelation: this is the mode in which all its truths are seen. In article 7, however, he is giving the obiectum quod. For what is principally revealable is God Himself, and all other things treated in the science are related to Him. God is what terminates and is attained by the habit of this science.

But what about the apparent discrepancy between the accounts of the object quo in the Summa and In Boetium De Trinitate? It should be noted that in the Division and Method, St. Thomas is working from the "top down". That is, he is making a general division of sciences, starting with the highest genera. On the contrary, in the Summa, he is asking whether the science is one, that is, whether it is indivisible, or an infima species of science. Therefore, there is no necessity that the formal object quo given in one work match the account given in the other work. In fact, the account given in the Division and Method, that is, under the light of immateriality of the sort that never exists in matter, seems to be applicable to Sacred Theology as held by us, by the blessed, and even (allowing analogy of the word "science") by God Himself. The light of revelation, however, is only applicable to Sacred Theology as held by us, making it an infima species and absolutely one science. Note especially that the subject, that is, the object quod of Sacred Theology is the same for the genus of Sacred Theology, or for the species of Sacred Theology as held by us: namely, God, or the first principle of things considered in Himself. This is further evidence that the most proper principle of dividing the sciences is by the object quo, as is done in the Division and Method.
____________________
1. See, for instance, Billuart in his Summa Sancti Thomae: "Nota: objectum, seu ut loquitur S. Thomas, subjectum, considerationis scilicet et non inhaesionis, duplex distinguitur in omni potentia vel habitu, nimirum materiale et formale. Objectum materiale est id quod a potentia vel habitu attingitur quidem, non tamen ratione sui sed ratione alterius. Objectum formale est id quod a potentia vel habitu attingitur ratione sui et ratione cujus caetera attinguntur. In objecto formale duplex ratio debet distingui: ratio quae, et est ipsa res quae attingitur, et dicitur objectum formale quod: et ratio qua seu sub qua, et est id quo mediante ratio quae attingitur: et dicitur objectum formale quo seu sub quo; ita ut ex hac duplici ratione quae et qua integretur objectum formale, quod est specificativum potentiae vel habitus. Sit exemplum in potentia visiva; objectum ejus materiale est corpus; formale quod, color; formale quo, lux; formale specificativum coloratum lucidum."

See also Cajetan in his commentary on the Summa: "III. Ad evidentiam huius rationis, nota duplicem esse rationem formalem objecti in scientia: alteram obiecti ut res, alteram obiecti ut obiectum; vel alteram ut quae alteram ut sub qua. Ratia formalis obiecti ut res, seu quae, est ratio rei obiectae quae primo terminat actum illius habitus, et ex qua fluunt passiones illius subiecti, et quae est medium in prima demonstratione; ut entitas in metiphysica, quantitas in mathematica, et mobilitas in naturali. Ratio autem formalis obiecti ut obiectum, vel sub qua, est immaterialitas talis, seu talis modus abstrahendi et definiendi: puta sine omni materia in metaphysica, cum materia intelligibili tantum in mathematica, et cum materia sensibili, non tamen hac, in naturali."