Molina’s doctrine is called scientia media, or middle knowledge, because it stands in the middle of the two traditional categories of divine epistemology as handed down by Aquinas, natural and free knowledge. It shares characteristics of each and, in the logical order of the divine deliberative process regarding creation, it follows natural knowledge but precedes free knowledge.
Natural knowledge is that part of God’s knowledge which He knows by His very nature or essence, and since His essence is necessary, so is that which is known through it. That is, the content of natural knowledge includes all metaphysically necessary truths. For example, the statement, “All bachelors are unmarried” is both necessary and part of natural knowledge. Other examples include other tautologies, mathematical certainties (e.g., 1+1=2), and all possibilities (since all possibilities are necessarily so). Natural knowledge can therefore be thought of as including a virtually infinite number of propositions of the form, It is possible that p, as well as a number of propositions of the form, It is the case that p. Thus, natural knowledge, properly conceived, is that part of God’s knowledge which could not have been different from what it is. It follows from this fact that the content of God’s natural knowledge is independent of His will; God has no control over the truth of the propositions He knows by natural knowledge. Consider, for example, the mathematical truth, 1+1=2. No matter what God wills, it will always be true that the concepts represented by the symbols 1, 2, +, and =, when arranged in a formulaic expression, one plus one equals two. It is important to note that, because natural knowledge is independent from God’s will and, to some extent, places limits upon the kinds of things God can do, natural knowledge informs(ed) God’s decision(s) regarding His creative work. This also means that natural knowledge is prevolitional.
Free knowledge is that part of God’s knowledge which He knows by His knowledge of His own will, both His desires and what He will, in fact, do. The content of this knowledge is made up of truths which refer to what actually exists (or has existed, or will exist). For example, the statement, “John Laing exists,” although certainly true, is dependent upon God’s choice to create me (or, more properly, to actualize a world where I am brought about), and hence, is part of God’s free knowledge. Free knowledge can therefore be thought of as including a number of propositions of the form, It is the case that p (Note that propositions of the forms, It was the case that p, and It will be the case that p, can be reduced to a proposition which refers to the present). Since free knowledge comes from God’s creative act of will, two things follow. First, the content of that knowledge is contingent; it could have been different from what it, in fact, is. That is, free knowledge includes only metaphysically contingent truths, or truths that could have been prevented by God if He chose to create different situations, different creatures, or to not create at all. Second, free knowledge is postvolitional; it is dependent upon God’s will.
As previously noted, middle knowledge is so named because it comes between natural and free knowledge in God’s deliberations regarding the creative process. According to the theory, middle knowledge is like natural knowledge in that it is prevolitional, or prior to God’s choice to create. This, of course, also means that the content of middle knowledge is true independent of God’s will and therefore, He has no control over it. Yet, it is not the same as natural knowledge because, like free knowledge, its content is contingent. The doctrine of middle knowledge proposes that God has knowledge of metaphysically necessary states of affairs via natural knowledge, of what He intends to do via free knowledge, and in addition, of what free creatures would do if they were instantiated (via middle knowledge). Thus, the content of middle knowledge is made up of truths which refer to what would be the case if various states of affairs were to obtain. For example, the statement, “If John Laing were given the opportunity to write an article on middle knowledge for the Internet Encyclopedia of Philosophy, he would freely do so,” although true, is certainly not necessarily so. I could easily have refrained from writing, if I were so inclined (or too busy, etc.). Likewise, its truth does not seem to be dependent upon God’s will in the same way that “John Laing exists” is. Even if God chose to not create me, the statement regarding my writing the article could still be true. In fact, its truth does not seem to be dependent upon God’s will at all, but rather upon my will. One of the basic assumptions of the doctrine of middle knowledge outlined above is that God cannot will a creature to freely choose anything. Thus, the content of middle knowledge can be thought of as including a virtually infinite number of propositions of the form, If person, P, were in situation, S, then P would freely perform action, A (or P(S®A)).
The theory of middle knowledge presents a picture of divine omniscience which includes not only knowledge of the past, present and future, but also knowledge of conditional future contingents (propositions which refer to how free creatures will choose in various circumstances), counterfactuals (propositions which refer to how things would actually be if circumstances were different than they are or will be), and counterfactuals of creaturely freedom (propositions which refer to what a free creature would have chosen (freely) to do if things had been different). This knowledge, together with natural knowledge, informs God’s decision about what He will do with reference to creation.
One of the most useful concepts for the explanation and evaluation of middle knowledge is that of possible worlds. The basic belief that things could have been different is commonly described as belief in many possible worlds. Each complete set of possible states of affairs (or way things could be) is a possible world, and although there is an extremely large number of possible worlds, it is not infinite (some states of affairs are impossible), and only one is actual (the way things are).
In the contemporary discussion of possible worlds, two concepts have proven particularly instructive: actualization and similarity. In popular piety, it is not unusual to refer to God creating the world. However, in possible worlds semantics, this is seen as semantically improper. Instead, God’s creative activity should be referred to as creating the heavens and the Earth, but actualizing a particular possible world (since possible states of affairs do not have a beginning, which the language of creation implies). According to the doctrine of Molinism, God can actualize a world where His will is brought about by the free decisions of creatures, but in order to make this claim, contemporary Molinists have had to distinguish between strong and weak actualization. Strong actualization refers to the efforts of a being when it causally determines the occurrence of an event (e.g., God causes something to happen), while weak actualization refers to the contribution of a being to the occurrence of an event by placement of a free creature in circumstances in which he will freely cause the event. Weak actualization has proven to be a powerful tool for understanding the relationship between God’s providence and human freedom. However, it must be noted that it implies that there may be some states of affairs that God cannot weakly actualize, which leads to the further conclusion that there may be some possible worlds that God cannot actualize.
A more controversial aspect of modern Molinism has been the use of possible worlds in determining the truth of counterfactuals. According to possible worlds semantics, a counterfactual is true in the actual world if it is true in the possible (but not actual) world that is most similar to the actual world. Not all Molinists have accepted this approach, noting the difficulty in determining comparative similarity among possible worlds.-http://www.iep.utm.edu/middlekn/#SSH3b.iii
