B15. PERSONS Finally we arrive at people. The theories of Part C are intended to some extent to apply to other kinds of agents than just people, such as robots and organizations, and some aspects of the cognitive theories, such as goals, plans, and beliefs, we would expect to find in any cognitive agent in some form. But many aspects are idiosyncratic to people -- accidents of evolution, in a sense. For example, there is probably no reason a robot or an organization should be thought of as having emotions. In Part C, when we are talking about aspects of cognition that apply to all cognitive agents, we will call the agent simply an "agent". When we are talking about particularities of people, we will condition the axioms on the relevant arguments being persons. A person is a kind of agent. (forall (p) (if (person p)(agent p))) (1) A person is also a kind of physical object. (forall (p) (if (person p)(physobj p))) (2) A person has a body and a mind. (forall (p) (3) (if (person p) (exists (b m)(and (body b p)(mind m p))))) In this axiom, b is person p's body, and m is p's mind. We won't restrict p to being a person, since animals have bodies and other cognitive agents can be viewed as having minds. All we need to know of the mind right now is that it is a composite entity. (forall (m p) (4) (if (mind m p) (compositeEntity m))) Thus, we can talk about entities external to the mind. A body is a physical object. (forall (b p) (if (body b p)(physobj b))) (5) A body is a composite entity whose components are body parts. In fact, it is a spatial system, since all the body parts are physical objects. (forall (b p) (6) (if (body b p) (and (spatialSystem b) (exists (s) (and (componentsOf s b) (forall (x) (iff (member x s)(bodyPart x p)))))))) A person p has a set of body parts, namely, the components of the body. (forall (p s) (7) (iff (bodyPartsOf s p) (exists (b) (and (person p)(body b p)(componentsOf s b))))) We won't explicate what the various body parts are. This would be a job for commonsense anatomy. But there are two distinguished subsets of body parts that are significant to our concerns -- sense organs and body parts that can be directly and voluntarily controlled. A person is capable of perception and action, and both of these require interaction between the body and the mind. These two subsets of body parts are what mediate perception and action. For now, we will simply posit a predicate "perceive", which is a relation between an agent and an entity or eventuality external to the mind. (forall (a x m) (8) (if (and (perceive a x)(mind m a)) (and (agent a)(externalTo x m)))) Ultimately, we will want to say how perception tracks reality. But this involves interaction with belief, inference, and action, and will be dealt with in Part C. Something being near a person is an enabling condition for perceiving it. (forall (p x e2) (9) (if (perceive' e2 p x) (exists (e1) (and (near' e1 x p)(enable e1 e2))))) In Chapter B14 we defined "near" in terms of the Hi region of a scale based on distance. Hi regions are related to functionality, and frequently perception is the relevant function. Something is near because it is near enough to perceive. The sense organs are a subset of the body parts. (forall (p x) (10) (if (and (person p)(bodyPartsOf s1 p)) (exists (s2) (and (subset s2 s1) (forall (o) (iff (member o s2)(senseOrgan o p))))))) It follows that sense organs are body parts. (forall (o p) (11) (if (senseOrgan o p)(bodyPart o p))) When something is perceived, there is a sense organ whose "intact-ness" enables the perception. (forall (p x e2) (12) (if (and (person p)(perceive' e2 p x)(Rexist e2)) (exists (o e1) (and (senseOrgan o p)(intact' e1 o)(enable e1 e2))))) The predicate "intact" will be explicated in Chapter C?? on goals, in the discussion of functionality. Another subset of body parts can be directly controlled by a person's will. That is, the person's willing an event is the direct cause of the motion of the body part. (forall (p s1) (13) (if (and (person p)(bodyPartsOf s1 p)) (exists (s2) (and (subset s2 s1) (forall (x) (if (member x s2) (exists (e1 e2 y z) (and (move' e2 x y z)(will' e1 p e2) (dcause e1 e2))))))))) In this axiom, s1 is the set of all of person p's body parts. The set s2 is the body parts p can voluntarily control. That is, for every body part x in s2, there is an eventuality e2 in which x is moved from someplace y to another place z, and this moving is directly caused by p willing it. In a more detailed account of human physical action, we could state in axioms specific facts about what actions are voluntarily and directly controlled by a person. For example, suppose we wish to state that a person can voluntarily lift his or her arm. The axiom would be as follows: (forall (p) (14) (if (person p) (exists (e1 e2 x) (and (lift' e2 p x)(arm x p)(will' e1 p e2) (dcause e1 e2))))) By contrast, we can move our hair by shaking our head or lifting our hair with our hands, but we cannot _directly_ cause our hair to move. We will explicate the concept of "will" in Chapter C??, when we discuss how intentions are converted into actions. Predicates Introduced in This Chapter (person p): p is a person. (body b p): b is p's body. (mind m p): m is p's mind. (bodyPart x p): x is one of p's body parts. (bodyPartsOf s p): s is the set of p's body parts. (perceive a x): Agent a perceives x. (senseOrgan o p): o is one of p's sense organs. The predicates "lift" and "arm" were used strictly for illustrative purposes and will play no further role. In addition, we used but have not yet explicated the following predicates: (intact x): x is intact and able to fulfill its function. (will a e): Agent a wills event e to occur. The predicate "intact" will be explicated in Chapter C??. The predicate "will" will be further explicated in Chapter C??.