Humean, All Too Humean

I intended this post to be a bit of reflection on agent causation and free will, but I was led in a more fundamental direction after concluding with Timothy o’Connor that an account of agent causation really depends on the impossibility of a Humean account of causation. This is a rather simple thesis that can be summed up as follows: agent causation (AC) takes as fundamental that causes really do necessitate their effects – let’s call this Real Causality (RC). Humean-ism (H) fundamentally denies that causes necessitate their effects. Therefore, the first step towards an account and defense of agent causation ought to begin with a look at the metaphysics of causation – more specifically, why we shouldn’t take H to be the case.

Tim Maudlin in his excellent volume ‘The Metaphysics Within Physics’ maps out H by way of two doctrines derived from a reading of David Lewis:

‘Doctrine 1 (Separability): The complete physical state of the world is determined by (supervenes on) the intrinsic physical state of each spacetime point (or each pointlike object) and the spatio-temporal relations between those points.’

‘Doctrine 2 (Physical Statism): All facts about the world, including modal and nomological facts, are determined by its physical state alone.’ (p. 51)

Maudlin then takes these ideas to task, drawing arguments against Doctrine 1 from quantum physics. Classical physics was indeed separable – the physical state of the universe is, more or less, determined by spatio-temporal relations, dispositions and properties in space and time. Maudlin spends a fair amount of time doing some pretty fancy math and comes to the conclusion that given quantum theory as a part of a true description of the world (which is a separate but related contention – Maudlin isn’t trying for an instrumentalist or consciousness-based interpretation of quantum theory here), separability cannot be sustained. He arrives here by an exposition of particle systems, spin states and entagled states, which is rather technical.

Doctrine 2 Maudlin takes to be indefensible as well, and I’ll quote him at length here:

‘It matters not whether one starts with Newton, who, in the Principia, simply announces his three laws of motion after giving the definitions of various terms, or whether one turns directly to any contemporary textbook on quantum theory, which will treat, e.g., the Schrodinger equation as a fundamental dynamical principle. Physicists seek laws, announce laws, and use laws, but they do not even attempt to analyze them in terms of the total physical state of the universe or anything else…Unlike reductive analyses of possibility, causality, and chance, reductive analyses of laws are not endorsed by scientific practice.

Indeed, scientific practice seems to preclude such an analysis. As we have seen, physical possibility is easily understood in terms of models of the laws of physics. Let us suppose (and how can one deny it) that every model of a set of laws is a possible way for a world governed by those laws to be. Then we can ask: can two different sets of laws have models with the same physical state? Indeed they can. Minkowski space-time, the space time of Special Relativity, is a model of the field equations of General Relativity (in particular, it is a vacuum solution). So an empty Minkowski space-time is one way the world could be if it is governed by the laws of General Relativity. But is Minkowski space-time a model only of the General Relativity laws? Of course not! One could, for example, postulate that Special Relativity is the complete and accurate account of space-time structure, and produce another theory of gravitation, which would still have the vacuum Minkowski space-time as a model. So under the assumption that no possible world can be governed both by the laws of General Relativity and by a rival theory of gravity, the total physical state of the world cannot always determine the laws. The only way out is either to assert that empty Minkowski space-time must be governed by both sets of laws, since it is a model of both, or (a more likely move) that it can be governed by neither set of laws, since neither is the simplest account of space-time structure adequate to the model (the simplest account is just Special Relativity). But how can one maintain that the General Relativistic laws cannot obtain in a world that is a model of the laws, and hence allowed by them? The necessity of distinguishing the physical possibilities (i.e. the ways the world could be given that a set of laws obtains in the world) from the models of the laws signals a momentous shift from philosophical analyses that follow scientific practice to analyses that dictate it.’ (p. 67-68)

There is no shortage of less physics-based reasons to not be a Humean, however. One might point out that Hume’s conclusions have force only if his empiricism is accepted, and there are many good reasons why that shouldn’t be accepted – modern philosophy is, in fact, partly composed of such rejections (Reid, Sellars, and the rejection of the positivists make up part of this history. The positivists, who claimed that non-analytic statements or statements that go beyond empirical justification are meaningless, are left in a position which doesn’t exactly aid one in the search for the laws of nature. Nor are things such as quarks and their flavors logical constructions out of sense-data). This isn’t to say that a wholesale rejection of Hume is called for – his observation that causation is not empirical is absolutely correct, though not his further conclusion that it doesn’t exist at all, since causation is very real though metaphysical category. But if the foundation for Humean-ism, which is a strict empiricism, isn’t sound, then we have far less reason to accept Humean-ism.

Given this all-too-cursory look at why we might not want to be Humean, what exactly follows? Concerning agent causation, we are left with a good bit of space with which to work, now that the shackles of Humean causation have been loosed – we are free to develop an account of agency and freedom in which agents are real causes of events.


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