One of the things that gets trotted out when someone argues that faith and reason are compatible is that many contributions to science or philosophy have been made by individuals who were religious. If faith and reason are incompatible, it is claimed, how can so many scientists and philosophers in history have been Christian (or Jewish, or Muslim, or...). But this quick argument--some philosophers are Christians therefore Christianity is reasonable, Q.E.D.--moves a little too quickly. Instead we need to ask questions about what role the idea of God plays in some particular thinker's philosophical system to assess whether his faith can be seen as truly consistent with his intellectual contribution: is the idea of God required for the system to be coherent? That is, is God a fundamental concept? Is the idea of God consistent with the rest of the system, but superfluous? Is the idea of God inconsistent with it? Because if God isn't required for, or consistent with, the wider system of thought, then it might be that all we really learn about the relationship of faith to reason from a religious philosopher is that people are capable of operating in spite of quite a lot of cognitive dissonance. One way to proceed with investigating the supposed compatibility of faith and reason would be to look at thinkers who were personally religious and see what role God plays in their systems. What kind of world do we get if we start with the assumption that God exists and work from there? In this post, I'll look at the very bizarre but apparently internally consistent system that Leibniz built on some standard assumptions about God.
The variety of theistic philosophers is pretty wide, ranging from thinkers who believe in God but whose systems don't depend on the idea (ex., Locke), to thinkers who base some isolated aspect or abstract goal of their projects on God (ex., Kant), to thinkers that hinge everything on the existence of a divine being. Leibniz falls into the third category. His whole philosophical system hangs on two assumptions that he shared with nearly every religious person who has ever lived: that God made the world and that God is perfect.
Leibniz held the very controversial doctrine that the actual world is in fact the best of all possible worlds. This view seems obviously false, but it falls out from the combination of his two assumptions. First Leibniz argues plausibly that if God is perfect then he will always act in the most perfect fashion, both metaphysically and morally (Discourse §1). The gist here is that in every case God acts in the best way that is possible. Since God is perfect, we have to assume that the world is as perfect as it could have been, otherwise God would have acted in an imperfect manner at one point or another. But God cannot act in a less than perfect manner without being himself imperfect (§3). Therefore this is the best possible world.
The laws of nature are taken by Leibniz to express the overall divine will of God in constructing the world in the best possible way. But while God designs the world through laws, we have to leave conceptual room for God to directly intervene in the world as well. Leibniz therefore divides the laws of nature into general maxims and subordinate maxims (§6). The general maxims are beyond our comprehension, so we only understand nature through the subordinate maxims, which can make nature look disorderly when the miraculous occurs (§16). Miracles may violate a subordinate maxim, but they can never violate a general maxim; even God’s extraordinary actions are consistent with the overall universal order he has created (§6). The laws of nature with which we are familiar, then, as subordinate maxims are not entirely exceptionless; if the suspension of a subordinate maxim is necessary to ensure that the course of events follows the general maxim, then such a suspension should be expected.
Another consequence of the idea of God creating the best possible world is that God must have foreordained (or at least must have foreknowledge of) everything that is going to occur; every individual thing or substance (including people) has its path laid out in advance, ensuring that God's perfect plan can be executed. Leibniz claimed that each individual substance (he called them "monads") must contain an internal principle of change (Monadology §11) because they are not affected by anything in the outside world besides God's intentions regarding what happens to them. This internal principle contains everything that will ever happen to the individual substance (Discourse §13). This notion is dependent on the idea of God in the sense that everything that will ever happen in the world must fulfill God’s design for the most perfect possible world. This means that the internal principle of the individual substance or monad must entail that every change it undergoes is in accordance with the general will of God.
Because Leibniz thought monads or substances could not be changed by external substances (other than God, of course), he had to explain the apparent interaction between body and soul. This was accomplished by appeal to God’s design in creating the world. God established at the time of creation a “pre-established harmony” that co-ordinates the actions of a soul and its body, even though souls act according final causes and bodies act according to efficient causation (Monadology §78, 79).
The existence and goodness of God and his creation also contribute to Leibniz’s solution of the problem of free will and determinism as well. In the context of theology, an obvious problem for Leibniz is that if the internal principle of a substance (or a soul) has determined its actions, then God, who created it, must be responsible for those actions ultimately.
In solving this problem, Leibniz differentiates between God’s antecedent will and his consequent will, which can be seen as the moral corollaries of the notions of general and subordinate maxims effective in the natural world. The antecedent will of God evaluates each possible good separately and desires its actualization. The consequent will of God is the total will, balancing all the conflicting goods of the antecedent will (Theodicy §22). God wills the good antecedently and the best consequently (§23). God permits sin, but does not approve of it (§24). God permits sin only to the extent that his consequent will requires it to fulfill the “rule of the best” (i.e., to bring about the best possible world) (§25). The will is exempt from constraint and from necessity (§34).
This does not mean that there is nothing that prompts us to choose, just that no necessity prevents our choosing otherwise (§35). While it is the case that the truth of future contingents is certain (§36) this does not mean that they are necessary. Necessity should be narrowly construed as logical necessity (§37). Even God’s foreknowledge does not make the future necessary (§38). This ability to act freely (in accordance with the internal principle) is not constrained by God’s foreknowledge (§42); God’s foreknowledge is simply based on the decisions that individual wills will make in the actual world God chose (because of its superiority) out of the infinitely many possible worlds. But God does not choose antecedently for any soul to sin. He merely chose as the best world (based on his consequent will) one in which some individuals would sin of their own accord.
So, what's wrong with Leibniz's view? Well, nothing, except there is absolutely no evidence for any of it--where is the proof that we're monads for whom events simply unfold according to an internal principle? Where is the evidence that there are deeper laws of nature that can explain so-called miracles in an orderly way? Is this really the best of all possible worlds? Even worse, if Leibniz's worldview were correct, how would we know? What does Leibniz give us to make empirical sense of the notion that bodies and souls have been pre-harmonized so as to fool us into thinking that they interact when they do not? Leibniz constructed an elaborate metaphysics derived in an orderly, logical fashion from some seemingly standard attributes of God, and wound up with a whole weird system of the world that bears so little resemblance to reality as we know it that it becomes difficult to even evaluate. At its best, it's a bizarre and complicated structure that is totally devoid of testable parts, as with the notion of preexisting harmony of the material and immaterial worlds. At its worst, it's so implausible that it ought to be dismissed out of hand, as in the notion that this is the best of all possible worlds.
Leibniz may be an extreme case, and one whose philosophy is more of an historical intellectual curiosity (there aren't many contemporary Leibnizians), but he's a terrific example of what happens when you try to start with concepts about God and deduce the world from them. You get a world unlike the one that really is.