Are Qualities Observable?

Nelson Goodman gives a very eloquent statement of what used to be the received view about properties, notably that only qualities are observable and thus knowable, and consequently ontologically basic because they can easily be thought of as intrinsic and fundamental properties of objects:

Besides the observable properties it exhibits and the actual processes it undergoes, a thing is full of threats and promises. The dispositions or capacities of a thing—its flexibility, its inflammability, its solubility— are no less important to us than its overt behaviour, but they strike us by comparison as rather ethereal. And so we are moved to inquire whether we can bring them down to earth; whether, that is, we can explain disposition-terms without any reference to occult powers.


Once powers are accepted as epistemically dependent on qualities and can only be characterised in terms of changes in the observable qualities, it invites the thought that they are also ontologically dependent and therefore properties that cannot be fundamental.

However, problems have emerged in this popular view to the degree that a survey of the literature reveals an array of conflicting statements:

(i) qualities are observable and thus knowable (Goodman 1954: 40), (ii) qualities are unobservable and in principle unknowable (Lewis 2007; Sparber 2009: 141-2), (iii) qualities are needed to make sense of powers (Ellis & Lierse 1994; Armstrong 1997; Ellis 2010), and (iv) we can only make sense of qualities in contrast to powers, as properties that do not have a dispositional essence (Armstrong 2005; Bird 2007#: Ch. 4.1). What is going on?

The reason for this confusion, I believe, is that‘observable’ means different things in different conceptual frameworks. Qualities may come across as observable if we take our unit of analysis to be our everyday lived experience, in particular if the focus is on the explanation of statements in natural languages, and naively understand whatever appears in our awareness as ‘what we see’. Also, if we endorse direct realism and assume that in perception we are directly acquainted with the object itself; that it is not mediated by phenomenal qualities. But if we believe conscious experience is a product of the senses in response to a stimulation by external objects, there is a problem. The problem can be formulated as a combination of what George Sparber calls the argument from humility and the argument from quidditism (Sparber 2009: 141-9), which work against MAP and in favour of fundamental powers.

It is important to note that I make no effort to prove indirect realism. I am merely pointing out consequences of holding certain views in an attempt to elucidate a framework in which it is possible to think of properties as both qualities and powers. I don’t aim to prove that everyone must think of them that way. However, I also believe that to point out such consequences has considerable force in the controversy I am addressing, because most of those engaged in the issue do accept some form of indirect realism. If you, dear reader, are an indirect realist, you have reason to pay attention.

Returning to the arguments Sparber identifies, if experience is produced by the senses in response to external stimuli, then powers are the only natural properties that can stimulate the senses to give rise to experiences. We now have two ways to argue for the same conclusion, first, from humility:

The argument from humility. If phenomenal qualities represent the properties that gave rise to them, then the only kind of properties represented in experience are powers. If the only properties we can know are those represented in perception, the only properties we can know are powers.

The argument aims to show that neo-Humeans, in so far as they accept indirect realism, put the cart before the horse; it is the concept of causally inert quality that is a theoretical posit whose nature cannot be known, which is inferred from observable powers. Alternatively, that neo-Humeans are assuming that natural qualities of external physical objects resemble the phenomenal qualities they are acquainted with in perception, only to realise they cannot explain how such qualities affect the senses. In this light, an ontology of powers appears to have an advantage, at least from an indirect realist perspective. Indeed, Lewis accepts the force of the argument and endorses Humean humility; he admits that the nature of the properties that make up the mosaic of local matters of fact cannot even in principle be known (Lewis 2007).

Second, from quidditism:

The argument from quidditism. If phenomenal qualities do not represent the powers that immediately gave rise to them, but instead the qualities that ground the power that can affect the senses, then the contingency of the connection between the causally inert qualities and the powers they ground means we cannot know whether the phenomenal quality that is the product of the exercise of powers correctly represents the quality.

The conclusion really is that the nature of neither qualities nor powers can be known.

Now, given this result, one may wonder why the notion of pure quality still has such a strong hold on the philosophical community. I think it is because the argument from observability isn’t the only reason qualities are found to be ontologically fundamental. There is an a priori argument that appeals to everyone, but it works its magic implicitly because the philosophical community seem oblivious of the influence it exerts.

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