The latter subject is the focus of some of his latest blog posts, and also something about which Rob and I recently had an exchange In , I argue that while Aristotelianism can in principle be reconciled with either the A- or the B-theory of time, the A-theory is by far the more natural view to take, and the presentist version of the A-theory especially. Rob disagrees, and argues that Aristotelian metaphysics is equally compatible with either theory or with some third, intermediate theory. We hash this out in some depth in the ACPQ exchange, and Rob repeats some of his main theses in the recent blog posts. Here I’ll reiterate some of my own misgivings about his position. the American Catholic Philosophical Quarterly.
The B-theory of time holds that past, present, and future things and events are all equally real, and that temporal passage and the now or present are illusory. The A-theory, by contrast, takes temporal passage and the now or present to be real. The presentist version of the A-theory also holds that, where time is concerned, only present things and events are real. (A presentist could allow that there are also things that exist altogether outside of time, either eternally or aeviternally.) The “growing block” version of the A-theory holds that present and past events are real. The “moving spotlight” version of the A-theory allows that past and future events are as real as present ones.
One of the issues that arises in the ACPQ exchange is whether the B-theory can accommodate notions of change and efficient causation robust enough for an Aristotelian. I argue that it cannot. Change and efficient causation, on an Aristotelian account, entail the actualization of potentiality. But it seems that on a B-theory, since all past, present, and future things and events are equally real, everything is actual, and there is no real potentiality. Hence there is no real efficient causation or change. The theory collapses into an essentially Parmenidean position, at least with respect to time and change.
Rob’s response to this is to suggest that a B-theorist could affirm both actuality and potentiality by speaking of relative actualities and potentialities. Consider a banana that is green at time t1, yellow at time t2, and brown at time t3. True, the B-theory holds that from an absolute point of view, times t1, t2, and t3 are equally real, and that the greenness, yellowness, and brownness of the banana are all equally actual. Nevertheless, relative to t1, only the greenness is actual and the yellowness and brownness are merely potential; relative to t2, the greenness is no longer actual but the yellowness is actual, and the brownness remains potential; and so on. Rob develops this proposal in his ACPQ article and briefly summarizes it in his recent blog posts.
But I don’t think this works. Here’s one problem with it. Suppose someone suggested that time was nothing more than a spatial dimension. I reject this view, and Rob wants to avoid it too. One problem with it is that it also seems incompatible with the existence of real potentialities in the world. If past, present, and future events are equally real in exactly the same way that the spatially separated hot and cold ends of a fireplace poker are (to borrow a famous example from McTaggart), then it seems that they are equally actual, just as the hot and cold ends of the poker are equally actual. There is no real potentiality in a spatialized conception of time, and thus no real change – and thus, really, no time either.
But suppose our imagined spatializer of time defended his view by saying that there is potentiality of at least a relative sort on his conception of time. Suppose he appealed to the poker analogy, and suggested that we could say that relative to the left side of the poker, the poker was actually cold but potentially hot, whereas relative to the right side, it was actually hot and potentially cold. Suppose he suggested that there was therefore a kind of “change” in the poker from left to right. And suppose he suggested that a similar kind of relative actuality and potentiality could be attributed to things and events at his spatialized points of time, and that a similar kind of change could therefore be attributed to them too.
In my view this would be clearly fallacious, involving little more than a pun on the word “change.” (See Aristotle’s Revenge for detailed criticism of spatialized conceptions of time.) I imagine Rob might agree, since, as I say, he too wants to avoid spatializing time, or at least denies that the B-theory need be interpreted as spatializing it. But I fail to see how Rob’s notion of relative actuality and potentiality captures real potentiality, and thus real change, any more than my imagined spatializer of time does.
Here’s another way of thinking about the problem. How does talk about relative actuality and potentiality capture real change or efficient causation any more than if we were to describe the objects and events of a fictional story as “relatively actual” (that is, relative to the story) even if they are from an absolute point of view merely potential (since the story is fictional)? We need to know what it is, specifically, about Rob’s conception of the relation between the banana’s being green at t1 and yellow at t2 that makes the transition from the one to the other any more a case of real change involving real causation than the events of a fictional story are.
In short, talk of “relative actuality” and “relative potentiality” by itself doesn’t seem sufficient to do the job Rob needs it to do. For we could use such language to describe an entirely spatialized conception of time, and yet it wouldn’t really give us genuine potentiality. Or we could use it to describe an entirely fictional world, and yet it wouldn’t give us genuine actuality. The notion of being “relatively” actual or potential seems – by itself, with no further elaboration – too thin to do the needed metaphysical work. (I criticize Rob’s position in more detail in the ACPQ paper.)