I have been searching the 'Net and various databases such as JSTOR without success for a good article on deus ex machina objections in philosophy. What exactly is a deus ex machina (DEM)? When one taxes a theory or an explanatory posit with DEM, what exactly is one alleging? How does a DEM differ from a legitimate philosophical explanation that invokes divine or some other non-naturalistic agency? Since it is presumably the case that not every recourse to divine agency in philosophical theories is a DEM, what exactly distinguishes legitimate recourse to divine agency from DEM? Herewith, some preliminary exploratory notes on deus ex machina.
1. Deus ex machina is Latin for 'God out of a machine.' Let us begin by making a distinction between DEM objections in literary criticism and in philosophy. A DEM objection can be brought against a play or a novel if the behavior of a character is not "necessary or probable" (as Aristotle puts it at Poetics 1454a37) given the way the character has already been depicted, or if an incident is not a "necessary or probable" consequence of earlier incidents. From a literary-critical point of view, then, a playwright or a novelist can be taxed with a DEM if he allows something to irrupt into the scene from outside it which doesn't fit with the characters and action so far depicted. As I understand it, the literal meaning of 'DEM' comes from the lowering of a god via stage machinery into the setting of an ancient Greek play. See, for example, Plato, Cratylus 425d where Plato has Socrates speak of "the tragic poets who, in any perplexity have their gods waiting in the air . . . ." If any novelist or playwright is reading this, he is invited to supply some examples of DEM and explain what is wrong with them.
2. My interest, however, is less literary and aesthetic than philosophical. In the context of philosophical and perhaps also scientific explanations, a DEM objection would be to the effect that illegitimate recourse has been had to an explanatory posit that belongs to an order radically other than the order of the explananda. I put it so abstractly because I want to leave open the possibility of DEM objections to explanations that invoke agents or powers other than God. We now consider two putative examples of DEM. The first is Leibniz's recourse to God in his solution of the mind-body problem and in his theory of causation generally, and the second is Malebranche's invocation of God for a similar purpose. What is particularly interesting is that Leibniz accuses Malebranche of deus ex machina, but does not consider himself liable to the same objection.
3. Leibniz, Psychophysical Parallelism, and Pre-Established Harmony. There are reasons to believe that psychophysical interaction is impossible. Indeed, Leibniz has reasons for denying intersubstantial causal influx quite generally, even between two material substances. And there are reasons to believe that (i) there are both mental events and physical events as modifications of mental and physical substances respectively and that (ii) these events are mutually irreducible. Suppose you accept both sets of reasons. And suppose you want to explain the apparent law-like correlation and covariation of mental and physical events, e.g., how a desire for a cup of coffee, which is mental, is correlated with the physical events that eventuate in your bringing a cup of coffee to your lips. Or, proceeding in the other direction, you want an explanation of why a hammer blow to a finger causes pain. Given that psychophysical interaction is impossible and that there are mutually irreducible mental and physical events, how explain the 'constant conjunction' of the two sorts of event?
One might be tempted by a theory along the lines of Leibniz's pre-established harmony. Roughly, on such a theory there is no intersubstantial causal interaction: the states of one substance cannot act upon the states of another. But there is intrasubstantial causation: the states of a substance cause later states of the same substance. So physical events in a body are caused by earlier physical events in the same body, and mental events in a mind are caused by earlier mental events in the same mind. Mental-physical correlation is explained in terms of pre-established harmony: "each created substance is programmed at creation such that all its natural states and actions are carried out in conformity with all the natural states and actions of every other created substance."(link) The explanation thus invokes God as the agent who establishes the harmony when he creates finite substances.
A standard analogy for the parallelism is in terms of two perfectly synchronized clocks. Whenever clock A shows 12, clock B strikes 12. There is an Humean 'constant conjunction' of striking and showing, but no showing causes a striking if 'causes' means produces or brings into existence. What accounts for the constant conjunction is the pre-synchronization by an agent external to the two clocks. Similarly with all apparent causal interactions: there are in reality no intersubstantial causal interactions, given the windowlessness of Leibnizian monads, but there are law-like correlations which constitute causation a phenomenon bene fundata. But these law-like correlations are grounded in the harmony among the internal states of the monads established when God first created the entire system of finite monads.
4. Now here is my question: Can one dismiss this Leibnizian scheme by saying it is a deus ex machina? Note that on Leibniz's scheme God plays an explanatory role not only with respect to the mind-body problem, but also with respect to the phenomenon of secondary or natural causation in general. For without the monadic harmony pre-established by God when he created the system of finite monads, there would be no law-like regularity such as constitutes causation in the phenomenal world.
Is the Leibnizian proposal a Deus ex machina or a legitimate form of philosophical explanation? The logically prior question is: What exactly is a DEM? I can think of five answers.
Answer One: Any appeal to a supernatural agent in a theory of natural phenomena is a DEM. On this latitudinarian understanding of DEM, any reference to God in a theory of causation or a theory of truth or a theory of objective value would be a DEM. If this is what is meant by a DEM, then of course Leibnizian parallelism is a DEM. But surely this understanding of DEM is entirely too broad and ought to be rejected. For it allows that any explanation of anything that invokes God is a DEM. But then the problem is not that Leibniz brings God into the theory of mind and body, or the theory of secondary causes, but that he invokes God to explain the existence of things. To give a cosmological argument for the existence of God would be to commit a DEM. So we can safely set aside Answer One.
Answer Two: An appeal to a supernatural agent in a theory of natural phenomena is a DEM if and only if no independent reasons are given for the existence of the supernatural agent. This is a much better answer. But then one will not be able to tax Leibniz with a DEM since he gives various arguments for the existence of God. The same goes for other philosophers such as Descartes and Berkeley who 'put God to work' in their systems.
But this second answer seems to have a flaw. Why would the reasons for the supernatural agent have to be independent, i.e., independent of the job the agent is supposed to do? Suppose the appeal to a divine agent takes the form of an inference to the best or the only possible explanation of the natural explananda. Then the appeal to the divine agent would be rationally justified despite the fact that the agent is posited to do a specific job. Accordingly, Leibnizian pre-established harmony could be interpreted as an argument for God as the best explanation of the phenomena of natural causation.
Answer Three: An appeal to a supernatural agent in a theory of natural phenomena is a DEM iff no reasons are supplied for the existence of the divine agent. This is an improvement over Answer Two, but a problem remains. Suppose a philosopher gives arguments for the existence of God, and then puts God to work in the phenomenal world. If the work he does involves the violation of natural laws, then his workings here below are miraculous in one sense of the term and for this reason philosophically objectionable. So we advance to
Answer Four: An appeal to a supernatural agent in a th eory of natural phenomena is a DEM if and only if EITHER no reasons are supplied for the existence of the divine agent, OR the working of the agent violates natural laws. But in Malebranche's system, neither disjunct is satisfied, and yet Leibniz accuses Malebranche of DEM. For Malebranche there is only one genuine cause and that is God, the causa prima. All so-called secondary causes are but occasions for the exercise of divine causality. Thus the occurrence of event e1 is not what makes e2 occur; God creates e1 and then e2 in such a way as to satisfy the Humean requirements of temporal precedence of cause over effect; spatiotemporal contiguity of cause and effect, and constant conjunction, which is the notion that whenever events of the first type occur they are contiguously succeeded by events of the second type. On this scheme, no causal power is exercised except divine causal power, which involves God in every causal transaction in the natural world. Leibniz objects that this is a DEM because it makes of each cause a miracle. (See Kenneth Clatterbaugh, The Causation Debate in Modern Philosophy, 1637-1739, p. 122.)
But it is not a miracle in the sense of the violation of a natural law. It is a miracle in the sense that the work that should be done by a finite substance is being done by God. A miracle for Leibniz need not be an unusual event; an event that surpasses the power of a natural substance can also be a miracle. Thus Malebranche's denial of causal efficacy to finite substances makes God's involvement in nature miraculous, which amounts to saying that the appeal to God is a DEM.
Answer Five: An appeal to a supernatural agent in a theory of natural phenomena is a DEM iff EITHER no reasons are supplied for the existence of the divine agent, OR the working of the agent violates natural laws, OR the agent's intervention in nature is miraculous in the sense in that it takes over a job that ought to be done by a natural entity. But if this answer be adopted, then Leibniz himself can be accused of DEM!