Power Mereology: Structural Powers versus Substantial Powers

Anna Marmodoro

Powers, and Only Powers

Ontologies are developed to explain phenomena in the world, rather than as inventories of what there is the world: it is therefore plausible to assume as an ontology’s guiding principle that one should countenance only entities that can make a causal difference to the world.1 Only they can have explanatory value; the inert ones appear to have none. This is the spirit of the so-called Eleatic Principle articulated by Plato and still influential in current metaphysics, that what exists is what can make a difference to the causal profile of the world, by bringing about or undergoing change.2 This principle is my point of reference in developing the neo-Aristotelian system that I call Power Structuralism. The principle says that what is real is what is powerful. I take what is powerful to be what can act causally upon something else or be acted upon, as well as what drives activity simpliciter. Thus, a causal power can exercise both in interactions with other powers, and in non-interactive activity.3

There are two ways one can proceed from here in developing one’s ontology further: either assume objects and show them to be powerful; or assume powers and show how objects consist of them. Power Structuralism follows the second path; the present paper aims to show how objects are built out of powers. My ontology has instances of physical powers as its building blocks: power tropes (e.g., an electric charge here and now) from which everything else is composed or derived. Such building blocks are the sparse fundamental properties in nature, as defined by David Lewis (e.g., mass, spin, charge); only that on my view—but not on Lewis’s—they are powers, essentially defined by the type of change (namely, interactions or noninteractive activities) that they or their possessors can bring about in the world.4 So, for instance, I take an electron to be composed of the power tropes mass, spin and charge; mass, spin and charge are the building blocks that make up the electron; they characterise the electron as its properties, and enable it to behave causally as it does in its environment.5 But the electron is not reducible to its compresent mass, spin and charge. These powers are not simply compresent in the electron; they are structured in relation to one another and, as I will argue, they furthermore compose into a single entity, the electron. The electron is the composition of the structured mass, spin and charge.6 (I will introduce the metaphysics underpinning this type of composition in section 4 below.)

The exercise of a power’s causal efficacy (i.e., the activation of a power as a non-interactive activity, or in changing something other than itself) is the ‘agential’ aspect of powers that the Eleatic Principle captures: powers are doers (even if, in some cases, the doings are simply activities, or even sufferings). For instance, the repulsive power of an electron is exercised when repelling another electron (while the electron is at once also repelled by the other electron, and hence is an agent as a sufferer as well as a doer). Since the electron need not be repelling or being repelled all the time (at least we can imagine it so, in thought experiments), we can think of the electron’s repelling powers as being, in some cases, activated and, in other cases, in potentiality. Generalising, what is characteristic of (interactive) powers such as the repulsive power of an electron is that they may or may not be activated. Herein lies an issue that has been much debated in the metaphysics of powers. What is a power in potentiality? More generally, what is potentiality?

With other metaphysicians (from Aristotle onward), I hold that powers in potentiality are real. They are not empirically detectable, because detection is interaction of a kind, and hence we detect only activated powers.7 On the other hand, powers in potentiality explain probabilities of interactive behaviour and change; in particular, they explain the readiness for certain kinds of interaction between elementary entities, and so they explain regularities of interactions we observe.

Having stated my own stance (for which I will argue in section 2), I turn now to set out some existing concerns in the literature regarding the existence of powers in potentiality. Two issues are under discussion. If powers in potentiality are admitted in the ontology, and powers are assumed to be the building blocks of all there is, could it be the case that the most elemental stratum of reality consists only of powers in potentiality? Must there be exercising (i.e. activated) powers at the fundamental level?8 One could attempt to construct an a priori argument for the conclusion that there need to be exercising powers at the fundamental level. I will not do so; my concern here is not that to argue there could not be worlds of mere potentiality, but to examine the range of actuality at the fundamental level of reality in our world.

Power ontologists by and large define the exercise or manifestation of a power as a relation between powers—one power in potentiality manifests by being replaced by another power in potentiality. But they thereby commit to worlds of mere potentiality, through and through, as David Armstrong famously objected. The argument is known in the literature as the Always Packing and Never Travelling Argument.9 Armstrong formulates it thus:

Given purely dispositionalist accounts of properties, particulars would seem to be always re-packing their bags as they change properties, yet never taking a journey from potency to act.

(Armstrong (1997: 80))

This argument raises difficulties for views on which the activation of a power in potentiality is merely an instantaneous ‘jump’ to its manifestation, which is another power in potentiality.10 On such views, when manifesting, a power is replaced by another power, which is also in potentiality. Worlds such as the ones to which Armstrong’s argument refers do include powers that manifest; but manifesting does not make them actual. They never go from potency to act; not because nothing happens in such worlds (since the powers do manifest), but because a power’s manifestation is an instantaneous transition to another power in potentiality. In a sense, powers here exercise by going out of existence. I submit that it is this conception of the manifestation of powers that commits one to a network of powers in potentiality only, where nothing is ever actual. This is precisely the complaint that Armstrong’s argument voices.

By contrast, Power Structuralism attempts to pay justice to the (intuitively compelling) thought that a power’s activation is the exercise of its powerfulness. Since actuality is the exercise of a power in Power Structuralism, it is numerically the same power that is first in potentiality and then manifests. This is a metaphysically novel position. It is a different conception of manifestation and of power from the existing ones in the literature, where potentiality and manifestation are different powers causally related. The causal relation, being contingent, gives rise to epistemological problems for the cognition of potentiality through the manifestation. These problems can be avoided if potentiality and manifestation are one individual.11 The oneness of potentiality and manifestation, as we will see below, also addresses the actuality problem raised by Armstrong.12 The idea is that powers endure transition from potentiality to activation—to being exercised. What, then, is it, on this account, for a power to be activated by being exercised? Is manifesting a property of a power; or a temporal phase of the power; or a state of the power? At the present stage of my research, I am not in the position to commit. I see two ways of analysing the metaphysical status of potentiality and manifestation, respectively. On the one hand, one can think of a power in potentiality and then manifesting as being metaphysically like an object at rest and then moving; on the other, a power being in potentiality or manifesting can be thought of as being metaphysically on a par with what in process ontologies is for a process to be processual, or what in particulate ontologies is for a particular to be particular.13

My thought is that a power may exist in potentiality and come to be activated; the power in potentiality and the activated one are numerically one. Powers can endure being exercised; they may also endure various types of alteration by being exercised, as, for example, their strength may increase or diminish, e.g., the strength of the electric charge of a discharging capacitor diminishes. Some powers may endure repeated manifestations, as, for instance, the repelling power of an electron.14 To understand how a power endures transitioning from potentiality to exercise it is helpful to recall that instantiated powers are tropes of physical powerfulness; they are real within nature, even if in potentiality. The physical presence of power tropes is the key characteristic that guides my account of how powers endure exercise, alteration and repetition.15 Power tropes in potentiality are physically present in the world; this is their reality. When they manifest, they produce change and we can detect them, leading to their knowability.

I hold that powers are physical entities, but also that what is physical is not essentially empirically detectable. This thought clashes with a common pre-theoretical assumption, that the physical is in principle empirically perceptible, even if not available for us to perceive in particular circumstances (as, e.g., ultraviolet rays are) or ever. If this assumption were correct, then one could not posit that a power in potentiality is a physical entity, because powers in potentiality are, as such, not detectable even in principle. On this line of thinking, then, a power in potentiality and its activation could not be numerically the same power, as I claim they are, because this would amount to a category mistake: a power in potentiality would become physical by being activated. I deny the pre-theoretical assumption as unjustified. There is physical continuity between the potential and the activated power, and between what is in principle non-detectable and what is detected. So a power in potentiality does exist because, when active, it can interact; the potential and the activated are one and the same power.

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