necessitas consequentis (necessity of the consequent): this is absolute necessity that refers to the opera ad intra.
Practical value of these distinctions: it allows the theologian to intelligently and without confusion speak of both necessary and free acts. Our acts are necessary in the sense that Providence is not subject to change. But our acts are not absolutely necessary, since God was not bound to decree such.
In short, freedom can be determined because freedom is not absolute (Asselt, 162-163).
Necessity of the Consequent, Consequence
The necessity of the consequent is the necessity of a proposition behind the “then” in an if…then statement. The necessity of the consequence is the consequence itself. Ie, the implicative necessity. In the implicative necessity, neither the antecedent nor the consequent needs to be necessary. Only the necessity of the implicative relation counts. Take the two propositions:
(1) If I marry Marian, then Marian is my wife.
(2) It is necessary that Marian is my wife (if I marry her).
In proposition (1) it is contingent that I marry Marian. I did not have to do so. Only the implication between the antecedent and consequent is necessary. In proposition 2 it is the result of the conditional proposition that is necessary.
Proposition 1 does not imply proposition 2. Therefore, in an argument of implicative relation of necessity, both the antecedent and consequent can be contingent and not necessary. According to the Reformed scholastics, the necessity of the consequence corresponds with absolute necessity and the necessity of the consequent with hypothetical necessity. In this distinction, the Reformed scholastics combat the charge that the divine decree destroys the contingency and freedom of the world. Therefore, necessity and contingency are compatible and not contradictory.
Most important in this distinction is that it depends on God’s will ad extra. If the decision of the divine will is directed to contingent objects ad extra, then God’s will is contingent, too. In other words, God contingently wills all that is contingent. Created reality, therefore, is the contingent manifestation of divine freedom and does not necessarily emanate from God’s essence. For if this were the case, all things would coincide fundamentally with God’s essence, and the actual world would be eternal (198-199).