Outline of a Naturalized Externalistic Epistemology Björn Haglund

1. The Problem In the essay “Epistemology Naturalized” (Quine 1969), W. V. Quine de- scribes a fundamental problem for epistemology as that of showing that statements about the external world around us can be derived from statements about our internal sensations. And he concludes (with David Hume) that this problem is unsolvable. But a related problem might be solved by standard scientific methods! He writes: The stimulation of his sensory receptors is all the evidence anybody has had to go on, ultimately, in arriving at his picture of the world. Why not just see how this construction really proceeds? Why not

settle for psychology? (Quine 1969: 75) And he later adds: Epistemology, or something like it, simply falls into place as a chapter of psychology and hence of natural science. It studies a natural phe-

nomenon, viz., a physical human subject. (Quine 1969: 82) In effect Quine thus proposes that we replace an impossible project by a more promising one. And he is not the first one to do so. With his ‘Copernican Revolution’ Kant invented the constructivist strategy for defeating Hume’s skepticism. In the Preface to the second edition of the Critique of Pure Reason Kant explains the gist of his new idea: Hitherto it has been assumed that all our knowledge must conform to objects. But all attempts have, on this assumption, ended in failure. We must therefore make trial whether we may not have more success in the task of metaphysics, if we suppose that objects conform to our

knowledge. (Kant 1787/1929: B xvi) Like Quine Kant thus accepts the Humean conclusion that knowledge about external, mind independent, objects cannot be gained from acquaintance with subjective sensory states. But unlike Quine he thinks that the way out of this dilemma must be to regard the objects of knowledge as internal (just like the sensations that carry information about them). 226

The main novelty lies in Kant’s new conception of the empirical, physical world, about which advanced scientific knowledge is possible. That world, the sensible reality in which we live, is — according to Kant — to a large extent a product (or construction) of our own minds. It therefore seems fair to regard Kant’s way around Hume’s problem as one of internalization. Quine’s proposed way of avoiding the problem leads in the opposite direction. 2. Naturalization and Externalism Science can teach us a lot about bats, but not what it is like to be one! (Or so they say anyway.) Subjectivity or 1-st person perspectives simply do not have any place in science, which is strictly confined to 3-rd person perspectives. The gap between 1-st and 3-rd person perspectives appears as unbridgeable as that between subjective experiences and their (assumed) physical causes. Some even think that it is one and the same cleft in both cases! “Externalism” is a term with numerous and various senses, depending on in which area (like ethics, semantics, philosophy of mind etc.) it is used. The sense in which naturalized epistemology is externalistic is that it adopts a scientific and thus a 3-rd person perspective on epistemic subjects or agents. In short, a possible motivation for naturalization of epistemology might go like this: For a cognitive agent it is impossible to relate and compare his or her own internal experiences to external sources. But for us, as external observers, the agents cognitive states and their physical causes are of the same kind, and thus on the same side of the unbridgeable cleft. 3. Interaction and Correlation Let’s start with a trivial example of information transitivity. Suppose that you want to find out the temperature of your environment, and have a mercury thermometer at hand. What you do is to find out the length of the mercury pillar, which of course is not at all what you actually want to know about. But the length of the mercury pillar is correlated with the volume of the mercury, which in turn is correlated with its temperature. And the temperature of the mercury is the same as that of the environment (as soon as thermal equilibrium is reached). To find out about one thing by finding out about something else is a quite common thing to do. 227

Today some of our neighbors in space (such as the Moon, the planet Mars etc.) are explored by means of space probes. Such probes are sent to, e.g., Mars, and once landed they sound their environment. That is, they interact with their environment in a way that ensures that their states become (partially) correlated to those of their surroundings. And thanks to those correlations we, on Earth, can learn about the surface of Mars by communicating with the probe. Radio signals carry information about the states of the space probe, and those states carry information about the state of Mars. This is but another case of information transitivity, and there is of course an abundance of such cases. Interaction often leads to correlation (that may be more or less strict), and correlation underlies information transitivity. An epistemically im- portant role of interactions in the forms of perception and action is to (partially) correlate states of agent and environment. 4. Coupled Systems Interaction leads to correlation. At least under certain conditions, which will be briefly described here by means of a few elementary notions from systems theory. A system1 is an entity that in every moment of time is in a state. The set of all possible states that a system can be in is called its phase space. Given two systems A and E, we can look at the combined system A⊗E, which has A and E as parts. Regarding the phase space of A⊗E, there are two possibilities. In the first case this phase space is isomorphic to the product of A’s and E’s phase spaces. This means that any combination of states of A and E is possible in A⊗E, and A and E are thus independent.2 In the other case some combinations of states of A and E are impossible. In other words states of one system can obtain only in combination with states from a proper subset of the other systems phase space. In this case the systems are said to be coupled, and there is a correlation between their states.

1 A system can be an entity of almost any kind. Think of cognitive systems, met- eorological systems, financial systems, computer systems, mechanical systems, etc. 2 Actually this is not quite correct, since there might still obtain statistical correlations, meaning that some combinations of states are more likely than others. But we will disregard this complication for now. Also complications having to do with the time development (or system dynamics) will be disregarded here. 228

This is what makes it possible for states of one system to carry information about the other system. Suppose, e.g., that s is a state of A. To s corresponds a subset E(s) of E’s phase space. If this subset is proper, then your information about E’s state increases when you learn that A is in s. 5. Correlation and Externalistic Epistemic Theory Suppose that we have a language AL, suited to describe and make claims about the ‘agent’ A and a language EL, suited to describe and make claims about the environment E of A. Our assumption is that the truth of sentences in these languages depends only on the state of the agent A and its environment respectively. Allowing a certain idealization this assumption means that if φ is a sentence in AL, there is a set A(φ) of states of A, such that φ is true (of A) if and only if A is in one of the states in A(φ). Similarly, if ψ is a sentence in EL, we assume that ψ is true (of E) if and only if the environment E is in one of the states in E(ψ). Suppose that A is in some state s ∈ A(φ), so that φ is true (of A). Since A and its environment E are coupled systems, the constraints obtaining means that the environment must be in one of the states in E(s), and suppose further that E(s) is a subset of E(ψ) for some sentence ψ in EL. We then have that ψ is true of A’s environment E. More generally: if E(A(φ)) = ∪{E(s): s ∈ A(φ)} ⊆ E(ψ), then φ is true (of A) ⇒ ψ is true (of A’s environment) This is a sentence in a common meta language of AL and EL. If AL =

EL the same fact could also be expressed by the sentence φ → ψ . But the normal way of expressing the corresponding (type of) fact, employed in, e.g., epistemic logic, is however to enrich EL with (‘epistemic’) operators and write, for instance,

KA(ψ) → ψ 229 which, by the way, is the so called truth axiom of epistemic logic, and can be read: if A knows that ψ, then ψ.1 This way of expressing a fact (ultimately resting on a correlation between states of A and states of A’s environment) also gives a prom- inent place to the notion of (semantic) content in the theory of cognitive (or information-carrying) states. The (propositional) content of ψ is simply embedded in the content of KA(ψ), and can of course be regarded as the content of the cognitive state which constitutes A’s knowledge. And this attribution of semantic content works even if A lacks linguistic of conceptual capacities! The semantic content derives from our external descriptions of A and A’s environment. So it’s OK to say of a dog that it knows that it is raining, or even of a Mars probe that it has discovered water. 6. Some Final Comments Does a theory, according to which it is all right to say that a thermometer knows the temperature of its surroundings, really deserve to be called an epistemology? Probably not, if you think that knowledge ought to be some kind of belief state and not merely an information-carrying state. And (as was once pointed out to Quine) traditional philosophical epistemology deals with normative questions of rationality and justifica- tion, and with analysis of central epistemic concepts. Naturalization would hardly help in such matters. So even if you think that the outlines sketched above can provide a promising start, there certainly remains much to be done! One may even wonder if it is possible for a naturalized theory to provide answers to all traditional epistemological questions. For a psychologist, a linguist, a sociologist, and certainly a natural scientist, it would be natural to assume, or take for granted, that his or her theories of cognitive agents must apply to him- or herself. After all he or she is a cognitive agent! So our naturalized epistemologist might be tempted to reason as follows: I have to grant Quine and Hume that I cannot discover and study the correlation between my own subjective experiences and their external sources. (And, being a naturalist, I am certainly not inclined to try Descartes’ way out of this dilemma! Nor

1 Stanley Rosenschein has shown that all axioms of an S5-type epistemic logic can be satisfied by an automaton coupled to its environment. See, e.g., Rosenschein (1987) and Rosenschein & Kaelbling (1995). 230

Kant’s, for that matter.) But wait a minute! I can observe the relations between the states of this other cognitive agent and their external causes. And eventually arrive at a theory of such relations. And since I and this other cognitive agent are of the same kind, and live in the same type of environment, the theory applies to me as well! So there is a way to build a bridge between the internal (immanent) and the external (transcendent) realms after all! But of course there is no solution to an unsolvable problem. To use a cognitive theory to give a 3-rd person description of me (as a cognitive agent) seems quite possible. But to transform a 3-rd person description of a cognitive agent (that happens to be me) to a 1-st person description of me seems as impossible as ever. And Thomas Nagel is probably right; no scientific theory about bats can tell you what it is like to be one! References Kant, I. (1787). Critique of Pure Reason, transl. by N. Kemp Smith, London: Macmillan, 1929. Quine, W. V. (1969). “Epistemology Naturalized”, in Ontological Relativity and Other Essays, New York: Colombia University Press. Rosenschein, S. J. (1987). “Formal theories of knowledge in AI and robotics”, Research Report CSLI-87-84, CSLI/Stanford. Rosenschein, S. J., & Kaelbling, L. P. (1995). “A situated view of

representation and control”, Artificial Intelligence, 73: 149–173.