The Challenge from Modern Science
The manner of characterising interactions between powerful particulars as involving a unidirectional exertion of influence by an Agent on a Patient, which results in a change in the Patient, goes back to Aristotle. One of the main points of this book is to point out that this characterisation is arguably incompatible with what modern science treats as an established fact, notably that all interactions are thoroughly reciprocal (Bunge 1979; Ingthorsson 2002, 2007). The fact that interactions are reciprocal is understood in the natural sciences to mean that there are no unidirectional actions, i.e. no instances of one object acting on another while not itself being equally acted upon by the other object (see, for instance, Resnick, Halliday, & Krane 2002: 83).
To be sure, the term ‘reciprocity’ occurs frequently in the contemporary literature on powers—it could even be described as a core concept in modern powers-based accounts—but it is then used with a very different meaning than in the context of natural science. The difference is that most powers-based accounts depict powers as reciprocal even though the influence exerted between two objects goes only from the one to the other. The term ‘reciprocal’ is here only an admission of the fact that at least two powers have to be involved, and that both contribute to the production of the outcome of the interaction. An example would be that the heat of the fire and the ability of a hand to be heated both contribute to the end result of a hot hand. This is the basis of distinguishing between an active power, i.e. the power of an object to influence another object, and a passive power, i.e. the power to be influenced by another object. It is also the basis for distinguishing between Agents and Patients, i.e. objects possessing active and passive powers, respectively. However, according to modern physics, no object acts on another object without being acted upon by the other in return (i) in the same way, (ii) to the same magnitude, and (iii) at the same time. If this is right, we no longer have any objective criterion to distinguish between an Agent and a Patient. Furthermore, if there are no unidirectional actions and the active/passive and Agent/Patient distinctions are mistaken then all notions deriving from or influenced by the idea of unidirectional actions also risk being false by the same measure. This flaw, although serious, is not fatal to the powerful particulars view. In previous work I have sketched a modified powerful particulars view that accommodates the reciprocity of interactions (Ingthorsson 2002, 2007). Indeed, as I will show in Chapter 4, the modification serves to strengthen the powerful particulars view. And, as I have already mentioned, it allows us to understand constitution and persistence of compound entities as causal phenomena, and reconcile (at least to some degree), substance and process ontologies.