affordances as dispositional propertiesMarch 2, 2007
We have been trying to define some rules how affordances should be described. One of the ideas was to use the operation verb, subject noun (with some of its properties), artifact noun (with some of its properties) as part of the description.
The philosophical paper by Scarantino goes much deeper adding ideas about not totally closed list of background circumstances, certainity or probability, goal and event as part of affordance descriptions.
I am not sure it will make the rule-definitions simpler in our case and should we try to apply his ideas, but at least we must be aware of what we are going to leave out.
Affordance properties ought not be treated by default as a homogenous block by theories of perception. They inherit from their constitutive relations with kinds of doings and kinds of happenings a number of distinguishing properties that are potentially relevant to establish whether they are perceivable, and, if they are, how they are perceived.
Gibson did not define phenomenology, but indicated the Gestalt psychologists Kurt Lewin and Kurt Koffka as representatives of a relational approach he wanted to improve upon. Lewin (1935) and Koffka (1935) described objects in the environment in terms of what organisms can do with them. For instance, Koffka ascribed to a postbox the relational property of having a ‘‘letter-mailing’’ demand character.
However, Gibson took phenomenologists to assume that the demand character is ‘‘bestowed
upon [the postbox] in experience, and bestowed upon it by a need of the observer’’ (Gibson 1979, 138). Instead, he wanted to define affordances so as to be able to say that the postbox is letter-mailing-with-able relative to an organism O independently of whether or not it is perceptually experienced as such, and independently of whether or not, once perceived, it is attended to by O (this will be contingent upon O’s needs). As he put it, ‘‘an affordance is not bestowed upon an object by a need of an observer and his act of perceiving it’’ ( Gibson 1979, 139). What bestows affordances upon items in the environment, Gibson suggested, are a set of real, or objective, or physical properties of the affordance bearer and the organism that are relevant to make a specific behavioral activity possible (e.g., grasping, catching, being eaten by).
Some puzzling remarks Gibson made about the ontological status of affordances:
An important fact about the affordances of the environment is that they are in a sense objective, real, and physical, unlike values and meanings, which are often supposed to be subjective, phenomenal and mental. But, actually, 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 (Gibson 1979, 129).
What Gibson wanted to say here, I take it, is that affordances are not subjective in the sense that they are bestowed upon the world in virtue of an actual or potential perceptual experience of a subject. According to the view I propose, the sense in which affordances are also objective is the sense in which a disposition in good standing has a basis constituted by objective properties.
Philosophical controversies flourish concerning what properties are, and what makes them dispositional.
To clarify the meaning of properties is to clarify the semantics of the predicates (if any) expressing them.
I follow Stephen Mumford (1998) in thinking that a predicate is dispositional or categorical depending on the way in which its ascription entails subjunctive conditionals.
Let us take two paradigmatic examples from the classes we want to distinguish, namely, fragility and triangularity.
The ascription ‘‘X is fragile’’ entails the subjunctive conditional ‘‘if X were (suitably) hit, then X would break,’’ and the ascription ‘‘X is triangular ’’ entails the subjunctive conditional ‘‘if X’s sides were (suitably) counted, the result would be three.’’
What Mumford (1998, 77) indicates as the fundamental ground of difference is that the entailment is by conceptual necessity in the case of fragility, but not in the case of triangularity. Roughly speaking, the idea is that the subjunctive conditional captures what being fragile means, whereas it does not capture what being triangular means (although is captures something that necessarily follows from what being triangular means).
The triangularity example was introduced by Mellor (1974).
I adopt from Elizabeth Prior (1985) the idea that dispositional predicates are best thought of as incomplete predicates. In the case of classic dispositions such as fragility, solubility, flammability, and so on, she suggests that the completer is a set of background circumstances C.
In other words, a bearer X is or is not fragile, or soluble, or inflammable not simpliciter, but given C. For example, the very same object X may be, say, fragile given a background temperature of 170 o C, and not fragile given a background temperature of 30 o C.
To clarify the semantics of an affordance ascription of the general form ‘‘X has affordance property A (at time t relative to an organism O in circumstances C)’’ is to fill in placeholders in a subjunctive conditional conditional that is entailed by the affordance ascription by conceptual necessity.
Such a conditional conditional has the following general form: At time t, if background circumstances C were the case, then (if a set of triggering circumstances T were the case, then a manifestation M involving X and O would be the case with probability p).
The idea that affordances are dispositions has already been explored by members of the Gibsonian movement, most notably Turvey et al. (1981) and Turvey (1992). The main problem with such contributions is that they introduce the idea that affordances and abilities are complementary and dispositional, but fail to explain what kinds of dispositions they are. The clarification of the semantics of dispositional predicates demands making explicit the subjunctive conditionals associated with them.
Under this view, affordance predicates are time-indexed incomplete predicates, whose completer is a set of background circumstances referring to an organism at a time in a set of environmental circumstances.
Two insights concerning C have to be kept in mind from the literature on dispositions.
The first is that the background circumstances C under which a disposition is possessed cannot be listed exhaustively, because they consist of an indefinitely large set. In fact, there is always some condition c that could be added to a specified set C such that, given C and c, any object X would no longer possess any given disposition.
The second is that the list of background circumstances C cannot be left entirely open ended, because there is presumably always some set C such that, given C, almost any object X would possess almost any disposition.
How should set C be accounted for then?
What concerns affordance predicates, we should rely on a tacit understanding of C as the set of normal ecological circumstances.
The trademark feature of affordances is that their manifestation is always constituted by an event in which the affordance-bearer X and the organism O are both involved.
I distinguish between two classes of affordances, namely, goal affordances (their manifestation is a doing) and happening affordances (their manifestation is a happening).
What makes an organism-involving event a doing rather than a happening is how the manifestation is related to the triggering circumstances. In the philosophy of action, the doing/happening distinction is commonly cashed out in terms of the distinction between events that respectively are and are not intentional under some description (Davidson 1980, 61). In other words, actions are typically understood as events triggered by an intention,
and such that there is a description of the event under which the intention is fulfilled (in the right way).
Roughly speaking, doings are events triggered by the selection of a goal, and such that there is a description of the event under which the goal is achieved (in the right way).
If it is true that, given background circumstances C, an organism O can at t engage in an event that qualifies as a doing or a happening M and involves X, then X is at t an affordance-bearer with manifestation M relative to O in circumstances C.
This being the case, an important determinant of what counts as an affordance property is how we interpret the modal force of O can at t.
I distinguish between surefire affordances (i.e., affordances such that the manifestation follows the triggering circumstances with certainty), and probabilistic affordances (i.e., affordances such that the manifestation follows the triggering circumstances with some positive probability p less than 1).
Sitability is now for me a candidate surefire goal affordance, and catch-ability and ride-with-ability are now for me probabilistic goal affordances of different degrees of reliability.