Tuesday 2 November 2021

Is Direct Perception Plausible? The Case for Affordances-as-Dispositions

The first post in this series laid out the rules for what makes a theory of perception direct or indirect. In order to avoid having to require organisms to somehow figure out behaviourally relevant properties (indirect perception), direct perception requires that such properties are out there already, ready and able to be detected. Such properties are a bit weird - by definition, they must be properties of objects that include some reference to the organism doing the detecting (specifically, they are impredicative properties). 

The second post laid out some reasons to think that such circularly defined properties are legitimate options for the physical world. Properties like this are required by the mathematics of the quantum scale; and so, while a bit weird, are possible. Organisms don't work with quantum properties, though, so if they only happen at that scale, this doesn't help a theory of direct perception. The key to making impredicative properties work is measurement. At the quantum scale, all properties are uncertain until measurement collapses the uncertainty of the thing measured. At the ecological scale, properties aren't uncertain in this way, but which properties are 'primary' still depends on the measurement device; to a polar planimeter, for example, the higher order property 'area' is simple and lower order properties such as 'length' must be figured out. The reverse is true of a ruler. 

We have a set of pieces now. Impredicativity requires measurement to affect which properties are immediately available to the measurer, this is possible at the ecological scale, and with the right measurement device higher-order properties can be immediately available. This establishes an in-principle case in favour of direct perception as an option. Next, if we can identify the higher-order form of behaviourally relevant properties, we will identify what kind of measurement device is required for these to be directly available. 

The main ecological hypothesis is that higher-order behaviourally relevant properties, which we call affordances, take the form of dispositional properties. This post will walk through how this works and how it fulfils what's required to support direct perception.

(As many of you know, not everyone is happy with the dispositional ontology, and propose instead that affordances are relations. I am not going to lay out the parallel case for how this ontology fulfils the requirements I have been laying out, for the simple reason that I do not think it can do any such thing and I have yet to see any successful attempt to make it work. I talk about this in this paper, currently still living in review limbo.)


Dispositions are higher order properties of physical objects that define something that the object is disposed to do, under the right conditions; something that is possible, although not currently happening. They are composed of lower order properties placed in some relation to each other, but it's the higher order disposition this arrangement makes that then acts as a property that can interact with other properties. In particular, the higher-order disposition defines a complementary higher-order disposition; when both are present, the dispositions manifest (i.e. become actual, rather than simply possible).

Take the disposition of salt to be dissolved in water. This disposition is constituted by the fact that salt is made of ions arranged in a strong but breakable lattice. If the positive ions are pulled one way and the negative ions are pulled in another, the lattice will come apart; the salt will dissolve. Notice that this dispositional property is inherently complemented by another dispositional property, namely the ability to pull the charged ions in different directions. Water has this property; water molecules have positive and negative ends and can pull hard enough to disrupt the lattice.

Dispositions are a little weird, but the weirdness is exactly the kind of weirdness we've been looking for. Specifically, they have the kind of circularity that is the hallmark of impredicativity. The disposition of salt to be dissolved is implemented by the material properties of the salt, but it is a property that is at the same time defined by the disposition of water to dissolve salt. You cannot simply predicate 'will dissolve' to salt, because salt will only dissolve under certain specific circumstances. The full physical account of this property requires reference to the complementary dispositional property of a solvent, and the conditions required to bring them together in a way that allows the disposition to become actual. 

Affordances and Dispositions

The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill....an affordance is neither an objective property nor a subjective property; or it is both if you like. An affordance cuts across the dichotomy of subjective-objective and helps us to understand its inadequacy. It is equally a fact of the environment and a fact of behavior. It is both physical and psychical, yet neither. An affordance points both ways, to the environment and to the observer.
Gibson, 1979, pg. 119
Gibson's definition gets accused of being vague and annoying, but immediately resonates with the facts about dispositions.  Dispositions don't sit comfortably within the objective-subjective analysis of properties, but are perfectly real, suggesting that analysis is inadequate. They are equally facts of the thing that has the disposition, and the thing that has the complementary dispostion. Dispositions also point both ways - if you characterise the disposition of salt to dissolve, you also characterise what is required of a solvent to make that disposition occur (this is how new solvents get invented!).

Affordances and Effectivities as Dispositions

So we seem to have a good match; dispositions are perfectly real properties, and they implement everything required to make them the kind of circularly defined things behaviourally relevant properties need to be. We have a viable ontology for things like affordances to be real. 

The specific ecological form of the dispositional analysis goes as follows. Objects in the physical environment are disposed to be acted on by an organism in some ways and not others. Those dispositions are higher-order properties of the object constituted by a particular arrangement of currently present material properties of the object, and we call these affordances. At the same time, organisms are disposed to be able to act on objects in some ways and not others. These dispositions are higher-order properties of the organism, constituted by a particular arrangement of currently present material properties of the organism, and we call these effectivities. Affordances and effectivities are just complementary dispositions, but we name them differently to keep track of them in our analysis, because it will matter which one we are talking about at any given time. 

When an organism encounters an object, one way it can do so is by bringing its effectivities into suitable contact with the object affordances. When it encounters an object this way, the affordance picked out by the effectivity is the 'simple' property, in the way area is simple to a planimeter and the way the disposition of salt to dissolve is simple to water. The effectivity and the affordance come together and their dispositions (to act on, and be acted on) are made actual; we have a behaviour. 


We are doing well in our bid to show that direct perception is, at least plausible, but we aren't all the way there yet. So far, we've shown that higher-order, impredicative properties are allowed, and that at the ecological scale the ones we need are called dispositions. While weird, they are perfectly legitimate properties and they are weird in just the ways we need. Affordances and effectivities, considered as dispositions, give us an ontology for describing the world in behaviourally relevant terms that can present themselves as properties, with no need to figure them out. 

We have one last hurdle to cross, however, and it's a doozy. I slid by it above - affordance dispositions and effectivity dispositions are legitimate ways to describe world and organism properties, but they only go from 'possibilities' to 'actualities' if the two can be brought 'into suitable contact' with each other. For things like salt and water, that suitable contact is physical contact; a glass of water next to a salt shaker does not count as the two being in suitable contact for the salt to dissolve. Organisms are almost never in physical contact with their environments; the only things touching me that way right now are my clothes, my chair, a small piece of floor and my keyboard. But I can behave with respect to affordances that are more distant; for the ecological account of how this works to work, we need to explain what 'suitable contact' means for affordances and effectivities. 

We need a theory of information. That's next.

1 comment:

  1. This was a very interesting read. Thank you for sharing your knowledge. You look worried about it not being well written, but I think you made a novice like me understand it.

    Regarding this issue, a doubt comes to my mind. Could it be said that dispositions are "hidden" properties of objects and that relational properties refer to emergent properties (what emerges from two (complementary) dispositions being in suitable contact?

    Thank you for reading my message.