. . . consider for a moment two persons, one with a serious smoking habit and the other without. Imagine the two walking together outdoors, away from the sight and smell of cigarettes. It may well be the case that in this setting there would not be anything present at that moment that would give rise in the heart of either person to a strongest inclination to smoke a cigarette. But if the two of them walked past an outdoor café where some people were smoking, just the sight and smell might elicit from the nature of the smoker a strongest inclination to light up a cigarette, whereas that same sight and smell might elicit from the nature of the nonsmoker a strongest inclination to walk quickly past the café and away from the smoke. In other words, what explains the choices each made is how their natures responded to the factors presented to them. Those factors do not cause the choices made, for notice that the factors were identical for the smoker and nonsmoker, yet the choices made by each were opposite in kind from one another. Nor would controlling the factors cause the choices made, because whether someone had “planted” smokers at that outdoor café or not would not affect the opposite choices of each in response. Rather, the causes of the respective choices were the two different natures of the respective individuals, each in response to the factors presented them, resulting in choices reflective of the natures of each person. The fact is, we act according to our natures, and what various factors in differing situations do is to elicit in each case the strongest inclination that our natures want in light of what factors are present. Perhaps we should think of God regulating the factors of a situation, then, as “occasioning” a particular choice to be made, rather than causing a particular choice to be made. Because God knows the natures of each person perfectly, he knows how those natures will respond to particular sets of factors presented to them. Thus, without causing a person to do evil, he nonetheless controls the evil they do. He controls whether evil is done, what evil is done, and in any and every case he could prevent the evil from being done. But in no case does he cause the evil to be done. In this way God maintains meticulous control over evil while his moral creatures alone are the agents who do evil, and they alone bear moral responsibility for the evil they freely do. 
1. Bruce Ware, "A Modified Calvinist Doctrine of God" in Perspectives on the Doctrine of God (B&H, 2008), pp. 118-119.