I. Although the knowledge of God is one and simple intrinsically no less than his essence, yet it can be considered in different ways extrinsically as to the objects. But it is commonly distinguished by theologians into the knowledge of simple intelligence (or natural and indefinite) and the knowledge of vision (or free and definite). The former is the knowledge of things merely possible and is therefore called indefinite because nothing on either hand is determined concerning them by God. The latter is the knowledge of future things and is called definite because future things are determined by the sure will of God. Hence they mutually differ: (1) in object because the natural knowledge is occupied with possible things, but the free about future things; (2) in foundation because the natural is founded on the omnipotence of God, but the free depends upon his will and decree by which things pass from a state of possibility to a state of futurition; (3) in order because the natural precedes the decree, but the free follows it because it beholds things future; now they are not future except by the decree.
Proof that no such middle knowledge can be granted.
IX. The reasons are: (1) Natural and free knowledge embrace all knowable things and entities and are not to be multiplied unnecessarily. There is nothing in the nature of things which is not possible or future; nor can future conditional things constitute a third order. For they are such either from a condition only possible or powerful, yet never to take place, or from a condition certainly future and decreed. In the former manner, they do not recede from the nature of possible things and belong to natural knowledge; in the latter, they are future and decreed by God and come under the free knowledge.
X. (2) Things not true cannot be foreknown as true. Now conditional future things are not true apart from the determination of the divine will; for example, the Sidonians would have repented if the powers had been supplied to them, for they would have been indifferently disposed in their nature to repent or not to repent, those powers being given; therefore from some other source ought to come the truth that they would repent, those powers being posited, if it is at all true. But no cause of this thing can be imagined except the will of God. There was nothing from eternity which could be the cause of the determination of a thing indifferent to either part except the will of God; not his essence or knowledge, for neither can operate ad extra separated from the will. Therefore, as no effect can be understood as future (whether absolutely or hypothetically) without the divine decree (because no creature can be in the world without the divine causality), so no future conditional thing can be knowable before the decree.
XI. (3) If all the acts of the created will fall under the divine providence so that none are independent and indeterminate, no middle knowledge can be granted (which is supposed to have for its object the free determination of the will, depending upon no superior cause). Now that there is such a subjection of the created will is evident from the dependence between the first cause and second causes, between the Creator and creatures. Nor can it suffice to save that dependence that the will may be said to be created and its liberty given by God for it would not cease to be the principle of its own determination, if its acts did not depend upon some decree. It would not be indeed the first being, but yet it would be the first operator (nor any more the second, but the first cause because if it depended in being upon God, it would not depend upon him in operation).
XII. (4) No uncertain knowledge should be ascribed to God. The middle knowledge can have no certainty because it is occupied about an uncertain and contingent object (viz., the indifference [adiaphorian] of the will). I ask, therefore, whence can God certainly know what will or will not take place? For either this can be done from the nature of the things themselves when he regards them (either in their causes or in themselves) as free acts in a created will (which pleases Bellarmine)—but how can an uncertain thing afford foundation to certain knowledge—or this can be done from the infinity of divine knowledge, which certainly foreknows in what direction moral persuasion will incline the will (otherwise free) to the opposite (which Vasquez and Suarez hold); but how could infirmity of knowledge change the nature of things and see a thing as certainly to take place which is contingent? Again knowledge either makes the event certain or foresees it as certain. If it makes it so, how can it foreknow it as such; where then is the indifference of the will? If it foresees it as certain, how could the foresight of an uncertain and indifferent thing be itself certain? Or from the eternal existence of things by which they are said to be present to God (as others prefer); but since they could have no real being from eternity (but only an intentional), they cannot be said to have existed from eternity otherwise than by reason of the decree in which they obtain their futurition. Since, therefore, the certain necessity of the event cannot be founded on the contingent connection of the ends or on the knowledge which recognizes but does not make the thing, it follows that it is only from the efficacious decree of the connector. Thomas Aquinas says most satisfactorily, “He who knows an effect contingent in its own cause only and not in some superior cause certainly determining it, has only a conjectural knowledge concerning it; since from an indifferent cause as far as it is indifferent, a determinate act cannot flow; and for the same reason from a contingent antecedent, as far as it is contingent, a necessary conclusion cannot flow before the decree of the divine will” (ST, I, Q. 14, Art. 13, p. 83).
XIII. (5) This middle knowledge takes away the dominion of God over free acts because according to it the acts of the will are supposed to be antecedent to the decree and therefore have their futurition not from God, but from itself. Indeed God would seem rather to depend upon the creature while he could decree or dispose nothing, unless a determination of the human will were posited which God would see in such a connection of things. Nor ought the reply to be made that the dominion of God is not therefore taken away because he can remove that connection or some circumstance of it; for example, in the foreknowledge by which God knew that Peter would deny Christ if placed in a certain condition, God could hinder him from denying Christ by taking away some foreseen circumstance (for instance, the fear of death) or by adding greater light in the intellect and a greater inclination in the will to confession, and the like. For it is not sufficient for the support of the dominion of God that he could hinder Peter from denying Christ, for he might have deprived Peter of life before the apprehension of Christ (but this would be to have dominion over the life of Peter, not over his free will); but it is requisite that the free acts of Peter, of denying or not denying Christ, should depend upon him (which is denied on the supposition of this knowledge). In fine, if God can take away one foreseen circumstance, he can therefore change the event of the thing: if he can by a decree change the event of a thing, therefore it also pertains to the decree to procure it; for he who hinders the event by a removal of some circumstance ought to cause it by supplying the circumstances.
XIV. (6) On the supposition of such a knowledge, a reason for predestination can be assigned out of God besides his purpose and good pleasure (eudokian) because the foreseen consent of the will of Jacob placed in such circumstances would be at least the condition without which God could not predestine to salvation Jacob rather than Esau. But no reason for that election can be derived from Paul except the purpose (eudokian) of God: “For the children being not yet born, neither having done any good or evil” not on account of a foreseen good use of free will through middle knowledge, but “that the purpose of God according to election might stand, not of works, but of him that calleth; it was said, the elder shall serve the younger” (Rom. 9:11, 12*). Nor should it be said that this condition is assigned on the part of God who has the knowledge, not of men; for although it is God who foreknows, yet the object which he foreknows is maintained to be the good use of free will foreseen before the decree, so that the reason of the decree is put not in God, but in man. Thus grace might with greater propriety be called the servant of the human inclination than the mistress, and the companion than the cause, making God depend upon man rather than man upon God.
—Francis Turretin, Institutes of Elenctic Theology, ed. James T. Dennison Jr., trans. George Musgrave Giger, 3 vol. (Phillipsburg, NJ: P&R Publishing, 1992–1997), 1.212–16.