A little bit of metaphysics can go a long way. This is a direct sequel to the previous post in this series.
There are objects in the world. We seem committed to saying that these objects have natures (of some kind), on pain of being able to say nothing about them. If there are natures that have some causality beyond bare regularity of succession, then there is something other than regularity in virtue of which things exhibit regularity, namely, the natures. However, if there is nothing to these natures beyond regularity of succession, the world begins crashing down around our ears (so to speak); they cannot do what they need to do. For one of the things a theory of natures must do is ground simultaneous causation. Whether one wishes to call it causation in a proper sense or not, it is clear that there are cases of simultaneous causation which require there to be some kind of causation that goes beyond regularity of succession. My computer monitor is currently caused to remain several feet above the floor by the desk (due to the desk's nature). This causation involves no regularity of succession, because it is not intrinsically successive. It's not the case that something is happening and then (as a distinct successor-event) the monitor is motionless several feet above the floor. Rather, the natural properties of the desk are what keep the monitor several feet above the floor while the monitor is above the floor. If, suddenly, the monitor were to fall through the desk to the floor, we could easily recognize that the properties of the desk had in some way, for whatever reason, changed. Clearly, then, there must be something to the nature of the desk beyond mere regularity of succession; and, whether we consider this to be a fundamental or a derivative form of causation, it is causal (beyond mere regularity of succession) in some way. It is clear then, that we have a positive reasons, of some sort, for denying the second thesis of RRTC. There is something causal about the world that explains regularity, and is not merely explained by it. If a bowling ball is on a mattress, it makes a dent; this denting of the mattress is not mere regularity of succession, because the ball's denting the mattress is not a distinct event from the ball's being of such-and-such nature while placed in such-and-such relation to a mattress of such-and-such properties. We see a crystal, and analyze it into its molecules; the properties and interactions of the molecules, as they exist in this crystal right now, are causing the crystal to have the structure it does. The natures in cases like this are contributing more to explanation than we can analyze into regularities alone.
Any plausibility that RRTC has depends crucially on RRTC's ability to deliver the world we actually experience. But the more one looks at the world as we actually experience it, the more obvious this truth becomes: our notion of the nature of an object (pick any object you wish) is a notion that is richer than RRTC can provide. A sign of this is just how rich our causal language (pick any natural language you wish) is. Another sign is that we never, in practical life, bank on there being nothing but regularity to causation. We suppose that there is more to the world than mere regularity; and what we suppose is that there are natures to things that cannot be wholly analyzed into resemblances among regularities of succession. In other words: we suppose there are reasons for regularities. We find positive grounds in experience for thinking this supposition right (as in cases of simultaneous causation), such that only it can actually do justice to the world as we experience it; we also find that acting and reasoning on this supposition (in prediction, retrodiction, application) shows it to be continually confirmed. Even the slightest bit of working with one's hands or interacting with the world gives ample evidence that RRTC cannot be right.
From this it is clear how one can answer the argument that was proposed in favor of RRTC; for there are many experiences of the world that cannot adequately be accounted for by RRTC. The only way to make our experience of the world seem in conformity with RRTC is to take experiences in isolation. If there were nothing more to my experience of the monitor on my desk than a mere glimpse, it might be reasonable to say that there is nothing more to it than a juxtaposition of colors. But when I take into account all my experiences of the monitor on my desk, and take them all together, it is clear that more is going on than can be accounted for by regularity of succession alone. There is more to the regularities than bare regularity, and my total experience of the monitor and desk gives me positive grounds for rejecting RRTC. However much one may try to play these down, they exist. The world I actually experience is not a world of mere successive stimulus and response; it is a world of structured objects capable of simultaneous interaction (however one analyzes this) and ordered dispositions and indispositions.
This goes not only for external objects like bodies; it goes also for the mind as well. It is entirely true that many of the regularities involved in my control over my body are completely mysterious to me; they are not transparent to experience. It is also clear, however, that there is more to my mental interaction to my body than successive events exhibiting regularity. My intentionally sitting still, for instance, cannot seriously be analyzed into succession of intention (as prior event) + sitting (as posterior event). However one may choose to analyze it, intentionally doing something cannot be analyzed in this way; but this is the only way in which RRTC can analyze it. What is clear for the mind's control of the body is even more clear for the mind's self-control. Even a basic puzzling over the answer to a problem provides grounds for thinking that there is more to the mind than RRTC suggests. And our interactions with other persons involve much the same reasoning. Even if RRTC could manage an analysis of these things as we actually experience them, such an analysis would have no advantages at all (and a number of disadvantages, such as complexity) over the more straightforward analysis that denies RRTC.
It should noted (and has been suggested briefly by a number of things already said) that it is not actually enough for the supporter of RRTC to argue that we don't actually experience a causal factor (beyond mere regularity of succession) in our experience of the world. The supporter of RRTC must argue as well that there are no positive grounds in our experience favoring the supposition of such causal factors over RRTC. Such a claim, however, is manifestly false, particularly when we go beyond carefully regimented and limited singular experiences and take into account our complete experience of the world. RRTC is simply not well disposed to explaining the world as we actually experience it.