In an earlier post, I began to write about John Hawthorne and Daniel Nolan’s analysis of teleological causation. (Eric has written about related topics too.) My aim there was primarily to summarize H&N’s analysis. Here I have some critical thoughts—I have only been thinking about this for a couple of weeks, so my opinions are far from final. H&N ask two questions: Is teleology coherent? Is teleology consistent with contemporary physics? Can it be added on? In my opinion, their analysis demonstrates coherence. (That's not a very high bar, but they clear it with ease.) I am less clear about consistency with physics.
Let’s start by considering the motion of a single particle. (I’ll consider ensembles of particles in a further post.) H&N distinguish three types of process (all more fully described in my earlier post): mechanical (for simplicity’s sake, Newtonian), retrotemporally mechanical (like Newton’s, but moving backward in time), and teleological or goal-directed. Since Newtonian trajectories are reversible—the temporal reversal of a trajectory is possible if the trajectory is possible—the paths of single particles do not distinguish between the first two options. If they are consistent with Newtonian mechanics, they are also consistent with time-reversed Newtonian mechanics. (See Eric Winsberg's comments on my earlier post.)
Now, Hawthorne and Nolan open the door to two ways of distinguishing goal-direction or teleological causation from both mechanical and retro-mechanical causation at the level of single particles.
In his preface to an edition of Galileo’s Dialogue on Two World Systems, Einstein noted that Aristotle’s universe is not isotropic; it has a privileged point. Galileo took an important step toward making the universe spatiotemporally uniform, when he realized that it was untenable to special points in space. Einstein’s own Theory of Relativity took further steps toward spatiotemporal uniformity first by treating all inertial frames of reference as equally valid, and then by treating certain alternative geometrical frameworks as equally valid.
Einstein’s observations highlight one way that teleology contradicts modern physics.H&N write:
Perhaps some contemporary trends in physics are as well served by teleological interpretations as any other. Systems of laws dominated by “principles of least action”, for example, seem to lend themselves to descriptions of systems primarily in terms of what they tend towards, or what they “aim at.”
In an otherwise brilliant article, this strikes me as glib. First, principles of least action are compatible with time-reversibility; teleology is not. Second, these principles do not contradict isotropy; teleology does. Of course, the suggestion might be that we should abandon temporal symmetry and isotropy, but this would be a substantive move, not just an “interpretation.”
I don’t mean this as a “gotcha”: it's possible that H&N meant this paragraph to be taken aporetically. But it is good to note that they are not shy about hinting at the possibility of revising modern physics, as when they talk about “anti-atomistic construals of the laws of thermodynamics.” My point is that any “teleological interpretation” of the principle of least action has substantive and far-reaching consequences for the basic principles of physics. They are not just "interpretations" as many distinguished theoreticians (including Ludwig von Bertalanffy, if I am not mistaken) have alleged. It's important to distinguish interpretations of physics from add-ons if we are to make progress towards clarifying what teleology might be.
H&N suggest another way to distinguish mechanical and teleological approaches by formulating frameworks for teleological dynamics. Consider a heavy particle removed from the centre of the universe. If released, this particle will begin to move toward the centre because it exists for the sake of resting at the centre. The question is: what path will it take to get there? This is a question that teleological dynamics ought to answer. The test of teleological dynamics is in how it handles interfering causes. What will the particle do if it meets an obstacle on its way to the centre?
Now, we know what mechanics tells us. A particle will come to rest if it arrives at a local topological minimum, or low spot, without the momentum that will carry it out. What about teleological dynamics? If it makes precisely the same predictions, teleology is dispensable. Why add it to mechanics if it yields no new predictions? Here is the kind of prediction one might expect a teleologist to add.
A teleologically guided particle will, to achieve its goal, overcome certain obstacles: under certain circumstances (stated), a particle will "swerve" to avoid what is in its way.
The capacity to come at a goal in different ways depending on circumstances is a definite indication of goal-directedness. And it would contradict mechanics.
In short, the teleological theorist is in a hard spot: either s/he must contradict modern physics or s/he must phase herself out of relevance. At the level of single particles, then, H&N have little wiggle room. Teleological dynamics had better contradict mechanics; otherwise, we have no reason to take it on board. Does teleology fare better with larger systems? I’ll deal with that question in a further post.