The ontology of dispositions

 The motivation for analysing the ontology of dispositions is to understand partial causes and objective chance. It is objective chance that is the stronger interest here, motivated by wanting to understand the behaviour of basic entities at the inorganic ontic level. That is, entities that fall within the remit of quantum physics.

 Dispositional properties, as described by Anjum and Mumford [1], will be used to clarify how there can be properties of quantum entities that cause quantifiable property values to appear and influence other objects. This will develop into a dispositional understanding of probabilities in quantum mechanics.

While it is easy to appreciate dispositional properties intuitively it can be harder to make the concept precise enough to be useful in constructing a scientific theory. To help the following definitions will be used: 

Definition 1

A disposition is a property (such as solubility, fragility, elasticity) whose actualisation entails that the thing which has the property would change, or bring about some change, under certain conditions. 

Definition 2

A dispositional power is a physically existing dispositional property of an entity. 

In everyday use to say that some object is soluble is to say that it would dissolve if put in some liquid. To say that something is fragile is to say that it would break if, for instance, dropped in suitable circumstances; to say that something is elastic is to say that it would stretch when pulled. The fragility (solubility, elasticity) is a disposition; the breaking (dissolving, stretching) is the actualisation of the disposition. These examples are intuitively uncontroversial, but position and momentum are not classical dispositional properties of a particle. Results such as that of Kochen and Specker [2] show that the quantum situation is more subtle than dispositional properties such as solubility and elasticity because they demonstrate a contradiction in assuming that it is possible to assign simultaneously values to all observable properties in all states. Their result, although called a paradox in their paper, indicates the need for an ontology that deals with this more subtle reality. 

There is still ongoing debate about the nature of dispositions and key elements of this debate are outlined in Mumford [3]. However, the application in physics makes the ontology of causal powers the more attractive interpretation of the nature of dispositions [4].  These powers exist and can be independent of an observer. 

With the motivation to provide an objective interpretation of chance in quantum mechanics Popper [5], [6] took a significant step towards a theory of dispositional properties. He took the position that quantum mechanics is a statistical description of the behaviour of physical entitles and introduced dispositional properties through his propensity interpretation of probability:

 ...waves (even those of the second quantization) are mathematical representations of propensities, or of dispositional properties, of the physical situation (such as the experimental set-up), interpretable as propensities of the particles to take up certain states. 

Popper proposed that the wave aspect of quantum mechanics determines the tendency of the particles to assume specific states under certain conditions but with the strength of this disposition given by a probably. However, Popper developed his thinking prior to the demonstration that it is impossible, in general, to assign intrinsic values to all observable properties in all states and he did not completely develop the ontological consequences. Popper remained committed to a physics in which particles have properties that take values as in classical physics but that the quantum theory provides a statistical description of that reality.  

It is proposed here that properties of a physical entity need not all take values simultaneously for them to be physically existing properties. Dispositional properties are properties that govern how the entity tends to appear in various contexts. For example, a separate physical system may be of the form that couples to an electron's spin in a specific direction and instantiate a value for it. That would be how the electron spin appears to that system. 

In the dispositional theory developed in this blog there are properties, objective causal powers, and in addition the probabilistic appearance of the properties as property values.  The concepts required to clarify what is meant by `to exist' and `to have a property' are set out in "Why critical ontology?" and Fields of Sense. 

Dispositional properties cannot themselves appear in a Field of Sense, but their effects can.  This is the point where the modification of the Field of Sense ontology is used that recognises that there are properties of objects that affect appearances but do not themselves appear. This modification means that Fields of Sense do not provide a complete ontology, contrary to what seems to be proposed by Markus Gabriel.

A dispositional property such as fragility appears if the fragile object breaks, on falling from a table, for example. This is how it appears in a domestic Field of Sense. The fragile object, for example a porcelain cup, exits and appears in the domestic scene even if it does not break. It also has properties that are not dispositional for example it has a mass. So, an object can have non-dispositional properties that pin it down in a context. The electron has the properties of charge and (rest) mass that pins it down in the physical universe in which it has, as will be explained elsewhere, dispositional spin, position, and momentum. 

So, the position taken on the ontology of dispositions is:

• Physical objects have at least one property that appears or causes a value to appear in some Field of Sense. 
• Dispositional powers cause property values to appear in Fields of Sense.
• Physical dispositions are properties of some physical objects.

[1] Rani Lill Anjum and Stephen Mumford. What Tends to Be. The Philosophy of Dispositional Modality. Routledge, 2018.

[2] Simon Kochen and Ernst P. Specker. The Problem of Hidden Variables in Quantum Mechanics. In: J. Math. & Mech. 17 (1967), p. 59.

[3] Stephen Mumford. Routledge Encyclopedia of Philosophy. Dispositions. 2011.

[4] Rani Lill Anjum and Stephen Mumford. Causation in Science and the Methods of Scientific Discovery. Oxford University Press, 2018.

[5] Karl R. Popper. Quantum Mechanics without 'The Observer'. In: Quantum Theory a

nd Reality. Ed. by Mario Bunge. New York: Springer-Verlag, 1967, p. 32.

[6] Karl R. Popper. Quantum Theory and the Schism in Physics. Unwin Hyrnan Ltd, 1982.

[7] Markus Gabriel. Fields of Sense. A New Realist Ontology. Edinburgh University, 2015.