Professor Scott Oliphint on a reformed perspective of free will:
... the event of the sin of Adam, for example, was an event that happened by way of the necessity of the consequence. God knows eternally that Adam will go wrong with respect to the forbidden fruit. His knowledge of Adam's action is infallible; the event itself is (hypothetically) necessary. Necessarily, once God decrees that it will happen, it will happen.
But that does not change the fact that Adam's decision to eat from the forbidden tree is a decision done by "a previous judgment of the reason and spontaneously." It is not coerced (in that there is nothing extrinsically forcing Adam's hand), and it is not against Adam's will (in that there is nothing intrinsically violating Adam's ability to choose for or against eating the forbidden fruit). Thus, the predetermination of God (by the virtue of the necessity of the consequence) and the freedom of man (by virtue of Adam's ability to choose among the options given) are not in competition with each other, nor does one violate the other. Rather, both are executed according to the providence of God, in which the application of God's decree includes the free decision of Adam to eat the forbidden fruit. Just as with the person of Christ, now with God's knowledge of human decision, God brings together both the divine (decree) and the human (free decision) under one unifying entity, providence, such that the two seeming incompatible properties are made compatible by his sovereign design and plan.
(Oliphint, K. Scott. Reasons [for Faith]: Philosophy in the Service of Theology. Phillipsburg, NJ: P&R Pub., 2006. Print. emphasis mine)