5.5 Analysis of generative sequences

Because generative sequences of derivative dispositions appear in a wide variety of contexts in both physics and psychology, let us formulate some concepts for the manner of their general operation. The first general idea is that ‘multiple generative levels’ are a sequence in which A ‘generates’ or ‘produces’ new forms of B using the present form of B as a precondition. We say that B derives from A as its manifestation. Then B generates C in the same way. This sequence may perhaps continue until an end Z, say, where the only activity is ‘selection’.

This rough scheme does not tell us, however, how A, B, etc might be changed as a result of the operation. Presumably this occurs often, as, for example, in naive quantum theory, when a wave function is changed after it generates a particular measurement outcome. It would be good to consider the philosophy for a general scheme to explain the (apparently mysterious) logic of the ‘reduction of the wave packet’. Let us extract some guidelines from our example derivative dispositions listed previously. To do this, we will need to distinguish the concepts of principal from instrumental and occasional causes.

5.5.1 Principal, Instrumental and Occasional causes

Davidson (1967) argues that causality is a two-place relation between individual events. Thus causal relations are not just implications from the description of the first event to that of the second event but are something more real. The reality of causality, however, does not automatically include such components as dispositions and propensities, although Steiner (1986) wants to extend Davidson’s ideas in this direction. Here, I want to allow both dispositions and previous events to be causes, although in different senses.

I recommend that distinctions be made between all of the following:

• the ‘principal cause’: that disposition which operates,
• the ‘occasional cause’: that circumstance that selects which disposition operates,
• the ‘instrumental cause’: the origin of the occasional cause, which is therefore another cause by means of which the principal cause operates.

All three kinds of causes appear to be necessary for any event in nature. For example, when a stone is let fall: the principal cause is the earth’s gravitational attraction, the occasional cause is our act of letting go, and the instrumental cause is the muscle movements in our finger releasing the stone. Its hitting the ground is thus caused by our letting go but only as an instrumental and then occasional cause. Many common uses of ‘cause’ (including that of Davidson (1967)) refer to occasional causes rather than principal causes, as it is only in this occasional sense that events can be said to be causes. Previous events cannot be efficacious causes, Emmet (1984) points out, in the sense of producing or giving rise to their effects, since events per se are not powers, but clearly they do make some difference when they happen. This is because events are the changes in powers, but change itself is not a power but rather the property of powers. The instrumental cause is a genuine causal contributor, and it may be said to set the stage by making suitable conditions (namely, the occasional cause) for selecting the operation of the principal cause.

I acknowledge that using the phrase ‘occasional cause’ brings in a certain amount of philosophical debate, but I see essentially the same questions occurring in many situations. We need some generic concept to refer to the circumstances, conditions, or occasions that must obtain in order for a disposition to manifest itself.

5.5.2 Causal sequences in physics

Consider now an electron of fixed charge and mass moving in an electrostatic potential according to classical electrostatics. At a given place x, the derivative of the potential V(x) gives the force, and the force gives the acceleration which in turn changes the velocity of the electron, and it moves to a new place. In our framework of derivative dispositions, we see that the potential is one disposition which generates another, namely the force. It does so according to the place of the electron. The electrostatic potential is therefore the principal cause of the force, and the place of the electron is the occasional cause. A place or any other spatiotemporal property by itself is never an efficacious cause, but it can be said to be the circumstance by means of which the potential generates the force. When we include magnetism and radiation, such properties will include velocities and accelerations.

Note that we never have forces causing potentials to exist where they did not before, nor do we have places causing forces to occur where they did not already exist. Let us generalize by surmising a set of generative levels {Potential Force Places}, such that the principal causation is always in the direction of the arrow, and the only ‘backward’ causation is by selection with an occasional cause. The only feedback ‘back up the sequence’ is with the conditional aspect of certain occasions. The specific operation of prior dispositions does not happen continually or indiscriminately. Operations of dispositions need to be selected from among all those that are possible, and thus there is an essential role for ‘particular occasions’ as preconditions.

Consider also the quantum mechanical evolution of a system from some initial time, such that it is subject to measurement selections at various later times. The quantum mechanical story is as follows. The initial quantum wave function is evolved according to the Schrödinger equation by a Hamiltonian operator up to the time of the first measurement. Any particular measurement implies a set of possible outcomes, and after the measurement, the wave function is changed immediately to one of those outcomes. The probability of each particular outcome is determined by Born’s law, namely that the probability is the square modulus of the overlap of the initial wave function with the possible resulting wave functions. The system then evolves according to the Schrödinger equation up to the time of the following measurement.

Seen in terms of derivative dispositions, the Hamiltonian is the disposition to evolve an initial state to new times, generating a new wave function according to the Schrödinger equation which contains that Hamiltonian operator. The new wave function is itself another disposition, namely a propensity to produce measurement outcomes with the various probabilities given by Born’s law. The final results are the discrete selection events at the times of measurement. These discrete events have only the minimal causal powers as they influence the future evolutions of the wave function. In that sense, they are just the ‘occasional causes’ according to which other dispositions may operate. The principal dispositions are first the Hamiltonian operator that starts the whole process and then the wave functions considered as fields of propensity for different selection events.

Summarizing the quantum mechanical case, we see that here again, the principal causes act forwards down a set of multiple generative levels whose range of actions at any time is selected from all those presently possible, as constrained by past events. Those events thereby become occasional causes. Because the wave functions before a measurement event are the cause of that event, those wave functions are the instrumental cause of the new wave functions after the measurement.

5.5.3 Conditional Forward Causation

We may generalize that all the principal causation is ‘down’ the sequence of multiple generative levels , and that the only effect back up the sequence is the way principal causes depend on previous events or occasions to select their range of operation. Let us adopt as universal this asymmetric relationship between multiple generative levels: dispositions act forwards in a way conditional on certain things already existing at the later levels. This is a simple initial hypothesis, and we will have to observe whether all dispositions taken as existing in nature can be interpreted as following this pattern.

We may therefore surmise that A, the first in the sequence, is the ‘deepest underlying principle’, ‘source’, or ‘power’ that is fixed through all the subsequent changes to B, C, etc. Conditional Forward Causation, the pattern we saw from physics, would imply that changes to B come from subsequent operations of A, and not from C, D,.. acting in reverse up the chain. We surmise, rather, that the subsequent operations of A are now conditioned on the results in B, C, D, etc. The operations of A are therefore the principal causes, whereas the dependence of those operations on the previous state of B is via instrumental causation, and the dependence on the results in C, D,... is via occasional causation. I suggest that this is a universal pattern for the operation of a class of dispositions in nature, namely those that do not follow from the rearrangement of parts of an aggregate object.

The terminology suggests that only forward causation occurs, so, for example, gravity affects objects on earth, but objects on earth do not affect gravity. Certainly that is the principal direction of causation. But note also the conditional or occasional part of the scheme, which describes how subsequent effects may yet have some effects on principal causes. How this works in mental stages will be discussed in Chapter 22, and its operation concerning gravity will be discussed in Section 24.5.