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Affordances are a pretty neat idea in the ecological psychology literature – they are used to explain how an actor’s behavior is modified by its environment. For example, a bear might find a good night’s sleep in a cave that a squirrel would be restless in. That same cave might be perfect for the squirrel to find food in, while the bear might have to venture outside to find a meal.

Using the work of [Chemero 2003], affordances can be said to be predicated on two things: environmental features and actor abilities.

Environmental features are to states of affairs what properties are to objects – both entail some kind of attribution. The difference is that while a property is tied to a particular thing, a feature is just attributed to a whole state of affairs (or environment) at once. For example, “it’s bright outside” attributes brightness to nothing in particular, just the whole outdoor scene.

Actor abilities are held by Chemero to be ‘functional properties’, as opposed to dispositions. The difference here is that functional properties can malfunction even in ideal circumstances (you can trip over yourself on a perfectly good sidewalk) while dispositions are guaranteed to manifest when properly triggered.

I prefer a different take on dispositions that relaxes the necessity of manifestation given a proper trigger, but Chemero’s heart is in the right place – actor abilities can’t be blatantly deterministic. If manifestation was readily deducible, animals would be understood more as robots than as free agents. And heck, we might all be deterministic robots running off highly complex algorithms at the end of the day. But until that time comes, it’s better to expect a bit of manifestation failure in our actors’ abilities.

Suppose that Stan, sitting in the downstairs kitchen of his house, wants to go upstairs. How can we represent and explain that the staircase is a solution to his problem?

Following Chemero, we have a staircase in the kitchen with six-inch risers. We also have Stan, who is capable of climbing stairs of this standard height. Our theory of stairclimbing only takes riser-height into consideration, so Stan can theoretically get upstairs.

In terms of representation, the first floor, staircase, second floor, and their spatial connections constitute a state of affairs. This state of affairs has the feature of a path between the first and second floors via the staircase. Stan has the ability to climb stairs when the riser height is less than one foot. All together, we can say that the house affords Stan the ability to go upstairs.

In casual symbols, we have a path from the first to second floor through a staircase with 6″ risers:

(instance-of :first-floor Floor)
(instance-of :second-floor Floor)
(instance-of :staircase Staircase)
(feature (path [:first-floor :staircase :second-floor]))
(riser-height :staircase (inches 6))

Moreover, we have a theory that an actor can move between two adjacent path elements if both elements afford movement. The adjacency of path elements can be inferred from the formal structure of the path vector indicated with square brackets.

(=> (and (adjacent-path-elements ?x ?y)
         (located-in ?a ?x)
         (affords ?x Movement ?a)
         (affords ?y Movement ?a))
   (ability ?a (move-to ?y)))

From this it’s straightforward to show that movement along a path of properly-afforded elements is both transitive and symmetric.

We have two supplementary theories about movement: floors always afford movement, and staircases afford movement if they can be climbed.

(=> (instanceOf ?x Floor)
    (affords ?x Movement ?a))
(=> (and (instanceOf ?x Staircase) (ability ?a (climb ?x)))
    (affords ?x Movement ?a))

Apart from the house, we have Stan on the first floor and his ability to climb normal stairs:

(located-in :stan :first-floor)
(has-property :stan :a)
(=> (and (has-property ?x :a)
         (instanceOf ?s Staircase)
         (riser-height ?s ?h)
         (< ?h (inches 12)))
    (ability ?x (climb ?s)))

So we can deduce that Stan can climb the staircase:

(ability :stan (climb :staircase))

And thus that Stan can move from the first to the second floor:

(ability :stan (move-to :second-floor))

Chemero’s theory has a nice structure to it, as it forces us to think about our situation in terms of abilities and actions. The feature thing is also nice, as it relieves us from predicating the path of a particular gerrymandered object.

However, this representation needs some work. The disposition stuff needs to be cleaned up, for one. It’s also not clear that the logic used above is appropriate – in many cases, logical descriptions can accidently cover up important ontological commitments or confusions. For example, the move-to clause in

(ability :stan (move-to :second-floor))

isn’t truth-functional, which means that the whole sentence isn’t from the normal predicate calculus.  So there’s work for next time.

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Imagine a big two-story house with 10 bedrooms, 8.5 bathrooms, and various specialized rooms (such as libraries, map rooms, dining rooms, and dens).  Oddly, there’s only one staircase in the whole house, connecting the den on the first floor to the library on the second.

The problem is to identify the rooms on an architectural diagram that let you go up to the second floor.  For many people, it’s sufficient to highlight the den, but consider somebody confined to a wheelchair: without a stairclimbing mechanism, the den fails to afford the ability to get to the second floor.

Pushing the example, let’s assume that our actor is indeed confined to a wheelchair, and there is an elevator in the first-floor kitchen.  How specific can you get when it comes to highlighting the things that afford the ability for our actor to go upstairs?  Highlighting the whole kitchen is a bit too rough, but the elevator itself is insufficient – there’s lots of wiring, a circuit breaker in the basement, a backup generator outside, power lines running to a power station, and eventually the water flowing down the Niagra River.

Finally, let’s simplify things with a futuristic elevator that requires no wiring and generates its own power.  Clearly, this elevator plays a part in affording our actor the ability to get to the second floor.  However, the design of the kitchen is also crucial: if the pathways to the elevator were too narrow, it would be impossible to navigate a wheelchair to the elevator in the first place.  Thus, there are different parts of the kitchen that fit together in a way that enables our actor.

Affordances are interesting phenomena when describing regions, because of their actor-dependence, their causal roots, and their basis in heterogeneous regional parts.  These features distinguish affordances from their relatively simpler kin, qualities.  Recent work has shown how to draw a line on a map that justifiably delimits a region characterized by a quality such as forested or populated.  It would be helpful to extend this ability to delimit regions that can be characterized as habitable, navigable, or defensible.

I hypothesize that recent work on construing dispositions as causal predications made true by processes is sufficient to establish a theory of affordances that meshes well with current work in ecological psychology.  Moreover, I argue that this theory would be suitable for extending granular theories of quality-based region delineation to encompass regions characterized by affordances.

In the late 1970’s, the notion of an affordance was coined by J.J. Gibson to describe the manner in which an individual’s environment plays a part in explaining the possible actions an individual can take. For example, a dog can drink water in a forest cut by a stream in a manner that would be impossible for that dog in a desert. Likewise, a tall tree provides an opportunity for a man to see beyond a nearby hill, an opportunity that fades when the tree is cut down.

An affordance, according to [Chemero 2000], is an “immediate opportunity for behavior” by an organism. To put it another way, affordances are relationships between agents and their environments that have some causal impact on how the agent acts. Moreover, these affordances are part of the way that agents look at the world: when you see a flight of stairs going up, you see a way to climb to a higher floor. For ecological psychologists like Chemero and Gibson, perception is not restricted to sights, sounds, tastes, touches, and smells. Beyond sense perception, agents see the things around them as instruments to be manipulated.

To make things sound more odd to the unacquainted, affordances are neither objective nor subjective relationships. Because an affordance is a relationship between an agent and something else, and the removal of the agent removes the relationship altogether, an affordance is not an objective thing that can be studied in isolation of its subjects. If you take the animals out of a forest, the stream running through it no longer affords the possibility of taking a drink: there can’t be any drinks if there are no drinkers. However, the existence of an affordance does not soley reside in the mind of an agent – it’s not subjective in the sense of a thought or emotion. Regardless of whether you believe that a dog can drink water without a source of water nearby, the dog will still be thirsty.

The odd nature of affordances can be better understood by considering the claim in [Chemero 2001] that affordance descriptions are not predicates – no property is said to inhere in any object in the environment. When we describe a stream as affording the opportunity to take a drink, we can’t merely stop with a formal representation that looks like

(affords-taking-a-drink   the-stream   that-dog)

Part of the reason is that it’s not just the stream itself as an object that affords drinking for the dog. The edge of the stream, for example, can’t be a five-foot cliff that would frustrate the dog’s efforts. The stream can’t be crawling with crocodiles, nor can it be frozen over. There are lots of features in the environment that together determine whether or not the dog can quench its thirst – the stream is only a convenient target for predication, not an accurate one.

Unsurprisingly, placement matters when it comes to possible activities. Some actions possible in a New Jersey motel are impossible on the surface of the moon. Thus, a principled way of describing affordances is needed that does representational justice to place and environment while avoiding the bog of fanciful what-ifs (heights, crocodiles, and ice).