NAGEL- Teleology Revisited

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Journal of Philosophy, Inc.

Goal-Directed Processes in BiologyAuthor(s): Ernest NagelSource: The Journal of Philosophy, Vol. 74, No. 5 (May, 1977), pp. 261-279Published by: Journal of Philosophy, Inc.Stable URL: http://www.jstor.org/stable/2025745

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THE JOURNALOF PHILOSOPHYVOLUME LXXIV, NO. 5, MAY I977

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TELEOLOGY REVISITED *GOAL-DIRECTED ROCESSESN BIOLOGY

ATURALISM' is the label for a number of distinctthough relatedphilosophical doctrines;but this is notthe occasion for listing their varieties or identifyingwhat is common to them. It does seem appropriate, however, to

begin these lectures with a reminder of the sense in which JohnDewey characterized his logical theory (or theory of inquiry) as"naturalistic." He so described his theory, because in it "there isno break of continuity between operations of inquiry and bio-logical operations" as well as physical ones, and because he be-lieved he had succeeded in showing that the "rational operations[of inquiry] . .. grow out of organic activities, without being iden-tical with that from which they emerge." 1 This summary accountof Dewey's conception of naturalism is not informative about thenature of the "continuity" he sought not to breach. However, itdoes make evident that for him biological processes and biologicaltheory constitute a substantial part of the matrix in which histheory of logic has its roots. Dewey also maintained that a touch-stone of whether Darwinian ideas (as he understood them) con-cerning logical method have been properly understood and assim-ilated, is the way the much-debated problem of "design versuschance" is treated.2 The conspicuous place this problem and its

* Presented as a pair of lectures, on Teleology Revisited, at Columbia Uni-versity in the spring of 1977; the first, "Goal-directedProcesses in Biology,"on March 28; the second, "Functional Explanations in Biology," on March 31.These lectures constitute the third series of John Dewey Lectures,which wereestablishedin 1967 to honor the late John Dewey, who had been from 1905 to1930 a professorof philosophy at Columbia. The editors are pleased to havethe opportunity to publish them.'Logic: The Theory of Inquiry (New York: Holt, 1938), p. 19.

2 The Influence of Darwin on Philosophy, and Other Essays in ContemporaryThought (New York:Holt, 1910),p. 9.26i


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262 THE JOURNAL OF PHILOSOPHYtreatment occupied in his assessment of the significance of Dar-winian theory for philosophy, testifies to the importance Deweyattached to the roles teleological notions play in biological inquiry.Dewey's interest in the issues raised by the use of teleologicalconceptions, is one reason for my choice of teleology as the themeof these Dewey Lectures. However, the debt owed to piety is notthe only reason. Although the ideas associated with the term 'tel-eology' have had a long and checkered history, and teleologicallanguage continues to be viewed with suspicion by many scientistsand philosophers, its use in biology as well as in the psychologicaland social sciences is widespread. Indeed, many biologists believethat such language is indispensable for describing and explaininga large variety of important biological phenomena. But despite thevoluminous literature devoted to analyzing teleological conceptsthat has appeared in recent years at an accelerated rate, there ismuch disagreement both over the meaning of teleological state-ments and concerning the kinds of events and processes aboutwhich it is appropriate to assert them. These disagreements arenot easily resolved for a variety of reasons. But whether or notthey can be resolved at all, it can be instructive to reexamine someof them in the light of fresh evidence and new perspectives on theissues at stake; and I want in these lectures to do so, though re-stricting myself mainly to questions that are germane to biology.The recent literature sometimes breaks fresh ground; but much ofit consists of modified (and sometimes much improved) versions ofwell-known views, presentations of difficulties in older analyses, orchallenges to basic assumptions underlying customary approaches.My discussion will, in consequence, inevitably revisit much famil-iar territory, though with some different objectives than on pre-vious journeys.A commonly recognized but loosely delimited trait of biologicalorganisms, a trait that is often said to distinguish living from in-animate things, is the apparently purposive character of livingorganisms. Teleological language reflects this distinction. Althoughthere is no exhaustive set of criteria for distinguishing teleologicallocutions from those which are not, the occurrence of certain ex-pressions in statements is usually a fairly reliable criterion that thestatements are teleological. For example, the statements "The pur-pose of the liver is to secrete bile," "The function of the kidneysis to eliminate waste products from the blood," and "Peacocksspread their tail feathers in order to attract peahens," are teleo


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GOAL-DIRECTED PROCESSES IN BIOLOGY 263logical; and the occurrence in them of the expressions 'the purposeof', 'the function of', and 'in order to' is a sure indication that thisis so. However, these are not the only expressions whose occur-rence in a statement marks the latter as teleological. There are alsostatements that are generally acknowledged to be teleological, eventhough they contain no typically teleological phrase-for example,the statement "The hare sought refuge in its burrow from thepacks of pursuing hounds." But despite the absence of a formalcriterion, there is little disagreement in actual fact as to whethera given statement is teleological or not.

Teleological statements are not all of the same kind, and theycan be classified in a number of ways. One distinction that will beuseful in what follows is between "goal ascriptions" and "functionascriptions." The former state some outcome or goal toward whichcertain activities of an organism or of its parts are directed. Forexample, each of the following is a goal ascription: "The goal ofthe pecking of woodpeckers is to find larvae of insects," and "Thegoal of the activities in various animals of the sympathico-adrenalapparatus as well as of certain cells in the pancreas, is to keep theconcentration of blood sugar within relatively narrow limits." Onthe other hand, function ascriptions state what are some of theeffects of a given item or of its activities in an organism. For ex-ample, the following statement is a function ascription: "Thefunction of the valves in the heart of a vertebrate is to give direc-tion to the circulation of the blood."

Some biologists use the words 'goal' and 'function' interchange-ably, ignoring distinctions that linguistic usage recognizes-theydo so possibly because the distinctions are not relevant to the taskson which they are engaged.3 But however this may be, seeing iscustomarily said to be a function of eyes, rather than their goal;and escape from a predator is said to be the goal of a hare's flight,rather than its function. Moreover, although the end products ofcertain goal-directed processes have a function-for example, onefunction of the homeostasis of sugar concentration in the blood isprevention of convulsions-this is not always the case-for ex-ample, survival may be the goal of a hare's flight from a hound,but survival itself does not appear to have any function. Also, thelachrymal glands have a function, namely, to lubricate the exposedsurface of the eyeballs, but do not have a goal. But the mainreason for retaining the distinction is twofold: the analysis of what

5 Cf. George C. Williams, Adaptation and Natural Selection (Princeton, N.J.:University Press, 1966), pp. 8/9.


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264 THE JOURNAL OF PHILOSOPHYconstitutes goal-directed behavior is different from the analysis ofwhat counts as a function; and secondly, the structure of func-tional explanations in biology differs from the structure of expla-nations of goal-directed behavior. The present lecture will be de-voted to the discussion of goal-directed processes in biology, andthe second one to functional explanations.

IIThere are a number of alternative (but not necessarily incompat-ible) explications of the notions of goal and goal-directed pro-cesses, and I will examine three of them. Undoubtedly the mostfamiliar account of these notions takes the primary (or "core")meaning of these terms to be determined by their use in connec-tion with purposive human behavior (and perhaps also in connec-tion with the supposedly purposive behavior of the higher an-imals). Accordingly, the "goal" G of an action or process is saidto be some state of affairs intended by a human agent; the inten-tion itself is an "internal mental state" which, coupled with theinternal state of "wanting" G together with "believing" that anaction A would contribute to the realization of G, is allegedly acausal determinant of the ensuing action A. "Goal-directed" be-havior is then the action A undertaken by the agent for the sakeof achieving the goal. For convenience of reference I will call thisaccount of goals and goal-directed processes the "intentional" view.

Several features of this account should be noted. In the firstplace, though the occurrence of the action A can be explainedteleologically, the explanation is ostensibly a species of causal ex-planation. For, by hypothesis, the action is initiated because theagent desires a certain goal and also believes that the action willcontribute to its production. The causal explanation cannot berightly charged with the difficulty often raised against teleologicalexplanations, that the causal explanation assumes that a futurestate of affairs can be causally efficacious in bringing about its ownrealization. For according to that explanation, it is not the goalthat brings about the action. It is rather the agent's wanting thegoal, together with his belief that the action would contribute tothe realization of the goal, that does so.In the second place, this account is fully compatible with theusual characterizations of goal-directed behavior. For example, hu-man beings are said to be goal-directed toward some goal, evenwhen they fail to achieve it; and this is congruent with the inten-

4 Andrew Woodfield, Teleology (New York: Cambridge, 1976), p. 104.


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GOAL-DIRECTED PROCESSES IN BIOLOGY 265tional view, according to which an action is goal-directed if it isundertaken for the sake of some intended goal, whether or not thegoal is reached. Again, goal-directed behavior is said to be "plas-tic," in the sense that the goal can be reached by alternative routesand from different initial positions, the route or action that isactually adopted depending on what local circumstances prevail.But such plasticity is obviously compatible with the intentionalview of goal-directed behavior; for the alternative actions that arerecognized as possible roads to the goal, as well as the action thatis actually adopted, will depend on the beliefs the agent has in thesituation in which he finds himself concerning the available meansfor reaching the desired end.On the other hand, if the intentional view of goals is taken lit-erally, an organism can be described as goal-directed with respectto a determinate goal only if it is legitimate to ascribe intentions,desires, and beliefs to the organism. In consequence, goals andgoal-directed behavior can be correctly predicated only of humanbeings, and possibly of some higher animals. It is therefore entirelyinappropriate to use such language in connection with organismssuch as protozoa and plants which are incapable of having inten-tions and beliefs; in connection with subsystems of organisms, suchas the complex of glands and other parts of the human body, thatare involved in the homeostasis of the blood temperature; or inconnection with inanimate systems, such as a steam engine pro-vided with a governor, and other servomechanisms that are some-times described as goal-directed.To permit the ascription of goals in some of these cases as well,some proponents of the intentional view have broadened the no-tions of goal and goal-directed behavior. According to Dr. AndrewWoodfield, for example, this more inclusive notion of having agoal is an extension of the "core concept" of having a goal-thatis, the concept of an intentional object of desire-to systems pos-sessing "internal states" analogous to the internal state of wantinga goal (ibid., 164). The goal-directedness of servomechanisms, hemaintains, "consists in the fact that they behave as if they had de-sires and beliefs in virtue of the fact that they are feedback sys-tems.... [T]he 'desired' end-state is encoded in their internal struc-ture" (193). If an internal state of a machine is to be described ashaving the goal G, the internal state must not only cause the ma-chine to behave in a manner that leads to G, but it must also"represent" G. However, Woodfield continues, "[t]here are no clearrules for deciding when an internal state is sufficiently similar to


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266 THE JOURNAL OF PHILOSOPHYa desire to count as the state of 'having a goal'" (195). Nor doeshe attempt to state necessary and sufficient conditions for an inter-nal state to count as a representation of the goal. He does notthink, for example, that an electronic feedback-subsystem, whichmaintains a steady output of current in the main system, is aninternal state of the latter sufficiently similar to a desire to countas the state "having a goal." Since there appears to be no signifi-cant material difference between such a system and either physio-logical homeostats or artificial thermostats, he excludes both ofthose from the class of goal-directed systems (196).

It is a plausible claim that the primary meaning of the phrase'being goal-directed' is stated by the intentional view; and it is notunreasonable to suppose that the current more inclusive sense ofthe phrase is a "metaphorical extension" of its initial meaning. Inany case, since biological inquiry deals for the most part withmatters in which desires and beliefs do not occur, it is obvious thatwere the phrase used strictly in the sense specified by the inten-tional view, it would have no application in most parts of biology.However, if the notion of having a goal that is not intended byanyone is held to be an impossibility, the sole consequence thatthis definitional resolution would most likely have is that a newword would be coined for the steady states achieved by physiologi-cal homeostats. Moreover, it seems to me dubious that there mustbe close analogies, as Woodfield maintains, between the items in-volved in the primary sense of the term 'goal' and those involvedin its more inclusive current usage. Nor does his requirement thatthere be such analogies, help to explicate the sense of goal ascrip-tions in biology. Consider his claim that the inner state represent-ing a goal in an ostensibly goal-directed biological process-forexample, the process in which a tadpole develops into an adultfrog-must "resemble" the inner state representing a goal that ispursued in some purposive human behavior, for example, the pro-cess in which a person seeks to recover a coin that fell into acrevice. In the latter example, the inner state according to Wood-field is a complex mental state involving an intention, a desire,and a belief. But in what way does the inner state representing thegoal in the former example-an inner state which is perhaps acomplex subsystem of genetic materials in the tadpole-resemble(or is it analogous to) a desire or a belief? It is not clear that thequestion really makes sense, and in any event it is difficult to knowhow to begin making the relevant comparison. Moreover, even ifthis hurdle is jumped, and it is assumed that the goal-directed


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GOAL-DIRECTED PROCESSES IN BIOLOGY 267development of the tadpole might be analogous to the goal-di-rected efforts of human beings, the analogy could surely not beestablished by comparing the inner states themselves. What mightbe established is that there is an analogy between certain behav-ioral features of the two goal-directed processes-for example, itmight be shown that both processes are plastic, and that both per-sist in the face of obstacles provided that these are not too great.In short, whatever may be the merits of the intentional view as ananalysis of goal-directed behavior of purposive human beings, itcontributes little to the clarification of the concept as it is usedin biology.

IIIThe second account of goal-directed processes I want to examineis sometimes formulated in the language of contemporary informa-tion theory, and more specifically in terms of the notion of a"coded program." I will therefore refer to it as the "program view"of goal-directed processes.As is well known, the materials physically transmitted from par-ents to progeny in biological inheritance are chiefly the genes lo-cated in the chromosomes found in the nuclei of cells. The genesthemselves consist of various kinds of very large molecules, amongothers nucleic acid molecules called DNA. The DNA moleculeshave a ladderlike structure, and contain four kinds of nitrogenbases in addition to other chemical groupings. Triplets of thesenitrogen bases are sometimes said to be "the letters of the geneticalphabet." Provided that no mutations have occurred in the in-herited genes, the sequential order of these "letters" in the longDNA molecules is then described as the "inherited information"(sometimes as the inherited "message" or "instruction") that con-trols the replication of the molecules, the development of thefertilized eggs, as well as the patterns of activity of the deveolpedorganism. Another way of stating this important conclusion ofmolecular biology is to say that the sequential order of thosetriplets is the inherited "program" that controls or places limitsupon, but without determining exhaustively, the development andthe numerous activities of the organism possessing it.It is this notion of program that has been recently used to ex-plicate the concept of goal-directed behavior; and I will examinethe proposal of Professor Ernst Mayr to define it. He first distin-guishes between two sorts of "end-directed" processes. Those hedescribes as "teleomatic" are processes that are said to be "reg-ulated by external forces and conditions," and to achieve their


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268 THE JOURNAL OF PHILOSOPHYend-state "in a passive, automatic way." 5 The motion of a stonedropped from a tower is an example of a teleomatic process, sincethe motion is governed by the external gravitational force, and itsend state is reached in an "automatic" way when the stone comesto rest on the ground.

The second sort of "end-directed" processes are called "teleo-nomic"-the word Mayr adopts to replace the more familiar ad-jective 'teleological', because the latter has been used to cover amiscellaneous assortment of phenomena, and has connotationsmany of which he wishes to exclude. He defines a "teleonomic"process or behavior as "one which owes its goal-directedness to theoperation of a program" (98); and a "program" is tentatively de-fined as "coded or prearranged information that controls a process(or behavior) leading it toward a given end" (102). Accordingly, aprocess that has no programmed end cannot properly be desig-nated as teleonomic. However, a program must not only provide"instructions" for achieving a goal; it must also "prescribe" physio-logical homeostats for dealing with internal and external disrup-tions of processes leading to the goal (99). The examples Mayr citesof teleonomic processes in biology include (either explicitly or byimplication) the migration of birds, the development of zygotesinto adult organisms, and the meiotic process that reduces thenumber of chromosomes in the sex cells of organisms to the hap-loid number found in the gametes.Two additional features of Mayr's account of the program viewneed to be noted. In the first place, his definition of "program" isadmittedly so constructed that no chasm separates ostensibly goal-directed behaviors in organisms from those of man-made machines.For example, he counts as programmed -procedures both the re-peated tossing of dice loaded so as to favor a given pair of sidesturning uppermost, and the behavior of a clock made so as tochime on the hour (103). In the second place, he counts as pro-grams both the closed programs controlling teleonomic processesin organisms that are fully contained in the DNA molecules, andthe open programs controlling teleonomic behavior, especially inthe higher organisms, that permit the incorporation of additionalinformation acquired through learning and other experiences. Forexample, the capacity for song of the white-crowned sparrow, as

5 "Teleological and Teleonomic: A New Analysis," in R. S. Cohen and M. W.Wartofsky, eds., Methodological and Historical Essays in the Natural and SocialSciences, vol. xIv of Boston Studies in the Philosophy of Science (Boston:Reidel, 1974), p. 98.


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GOAL-DIRECTED PROCESSES IN BIOLOGY 269well as the species-specific skeleton of the song, are controlled bythe inherited program of these birds; but the population-specificregional "dialect" of the song is learned, so that in respect to thedistinctive regional features of the song the program is an openone.6 How various portions of a program come into being-whethertransmitted genetically or acquired by learning-has therefore nobearing on the question whether the program leads to a "predict-able goal." 7

As has been already noted, the concept of programmed biologi-cal processes is based on some remarkable findings of molecularbiology, and it introduces a unifying perspective on importantfeatures of goal-directed behavior. However, the relevant questionin the present context is: What does the concept of programmedaction contribute to the clarification of the notions of being a goaland being goal-directed as these are used in biology?

(a) In the first place, it is obvious that in general we do notascertain whether a process is goal-directed by examining the pro-gram that controls it. The coded information that constitutes theprogram is a complex physicochemical structure in the DNA mol-ecules located in the genes of the organism under discussion; andat present, at any rate, we do not know just what is the specificphysicochemical structure that corresponds to a given process. Wedo not know, for example, just what is the sequence of nitrogenbases in the DNA molecules that corresponds to, and is the pro-gram for, the meiotic process in cells or the singing of sparrows.Moreover, even if we did know know these correspondences, itwould be quite difficult to ascertain for a given organism what iscontained in its coded program. Accordingly, there must be someother ways of finding out than by consulting-its coded program,whether a given process is goal-directed, and if it is just what is itsgoal. There are indeed such other ways. It is at least a plausibleconjecture that an examination of these other ways is more likelyto provide effective criteria for identifying goal-directed processes,than would an inspection of coded programs.

(b) In the second place, the fact that a process is controlled bya program does not suffice to make the process a goal-directed one,unless it is made so by definition. But if such a definitional maneu-ver is not adopted, a program will correspond to a goal-directedprocess only if the program is of a special kind. For example, theknee-jerk reflex action in normal human beings, which is mani-

6E. 0. Wilson, Sociobiology (Cambridge, Mass.: Harvard, 1975), p. 157.7 Mayr, op. cit., p. 104.


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270 THE JOURNAL OF PHILOSOPHYfested when the tendon below the kneecap is tapped, is presumablycontrolled by an inherited program. However, this is not a processthat is commonly regarded as goal-directed, chiefly because (as Ithink) it lacks persistence-that is, should some internal distur-bance prevent the knee jerk from taking place, even though thepatellar tendon is tapped, the human body is not equipped withany mechanism for making appropriate compensatory responses tothose disturbances. It is thus evident that it is possible to state atleast some of the conditions a process must satisfy if it is to be agoal-directed one, in terms of the manifest features of the process.But no one has yet succeeded in stating, in terms of the compo-nents and structures of DNA molecules, what requirements a pro-gram must satisfy if it to count as one that controls a goal-directedprocess. Accordingly, if we do not have some idea of what goal-directed behavior is-an idea that, however vague it may be, isacquired and understood independently of Mayr's formal defini-tion of teleonomic processes-the formal definition will neitherconvey the idea, nor provide instructions for applying it to bio-logical phenomena, nor clarify the notion of being goal-directed.

(c) In the third place, although Mayr's distinction between closedand open programs is an important one, it is debatable whether heis correct in claiming that the origin of a program has no bearingon the question whether the program leads to a "predictable goal."For it is an empirical matter that cannot be settled a priori, whetherpredicting the goal of a process on the assumption that the processis open, is as reliable as the prediction of a goal when it is knownthat the process is closed. I do not know whether a serious study ofthis question has ever been made. It is my impression, however, thatthe available evidence favors a negative answer to this question. Onthe other hand, it is at present difficult if not impossible to ascertainby actually examining a program, as distinct from the overt processit controls, whether the program is closed or open. The distinctionis therefore of no help at present for deciding whether a given pro-cess has a predictable goal.

(d) Finally, it would be pointless to explicate the notion of beinggoal-directed, if all processes whatever were just of that sort-thatis, if processes said to be goal-directed did not differ in some identi-fiable respect from processes not so characterized. But althoughMayr sees this clearly, it is not clear that the distinction he drawsbetween teleomatic and teleonomic processes with the intent of ex-plicating that difference, attains his objective.It will be recalled that teleomatic proceses are said by Mayr to be


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GOAL-DIRECTED PROCESSES IN BIOLOGY 27I

"the simple consequences of natural laws" and are "regulated byexternal forces." However, if the earmark of a teleomatic process isits regulation by "external forces," then the process in which aradioactive substance such as uranium radiates energy is not teleo-matic. For the process is not controlled by conditions external to thesubstance. Moreover, if it can be said that this process is "pro-grammed"-despite the fact that the word would then be used,following Mayr's own practice, in a sense far more inclusive thanthat associated with the word in molecular genetics-the processmust therefore count as teleonomic. But this is contrary to what Ithink is Mayr's intent, as well as to what would be generally main-tained. One of his examples of a teleomatic process is the behaviorof a rock dropped into a well; and one of his examples of a "pro-grammed" (and presumably teleonomic) process is the behavior ofa clock built to strike on the hour. Now the rock's behavior is surelyteleomatic and not goal-directed, for it arrives at its end state "auto-matically." However, since the clock's behavior is also the conse-quence of relevant laws of nature conjoined with a number ofboundary and initial conditions, it is difficult to see why this be-havior should not also be described as teleomatic, and as reachingits recurrent end states automatically. I do not know how to escapethe conclusion that the manner in which teleomatic and teleonomicprocesses are defined, does not provide an effective way of distin-guishing between processes in biology that are goal-directed fromthose which are not. In consequence, though the program view notessome important features of goal-directed processes, it is not an ade-quate explication of the concept.

IVThe third account of goal-directed behavior I wish to examinemakes use of some of the ideas, though for the most part not thelanguage, of cybernetics, systems theory, and what is known as the"organismic" standpoint in the philosophy of biology. For reasonsthat will soon be apparent, I will refer to it as the "system-property"view of goal-directed processes.

Partial anticipations and variant expressions of some aspects ofthis view can be found in a number of writers; but until the publi-cation at mid-century of a somewhat neglected book by Gerd Som-merhoff, it had no precise systematic formulation.8 Sommerhoff'sprincipal aim was to state the general conditions a process mustsatisfy if it is to be classified as goal-directed, irrespective of the

8 AnalyticalBiology (New York:Oxford, 1950).


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GOAL-DIRECTED PROCESSES IN BIOLOGY 273of numerous muscles and the skin, all of which can release storedwater into the bloodstream; and let M be a variable, whose valuesindicate the amount of water so released. It should be noted thatthese variables are independent of (or "orthogonal" to) each other,in the sense that within certain limits the value of either variableat a given moment is compatible with any value of the other var-iable at that same moment.9 As will be seen presently, such orthog-onality of variables is an important requirement. If now a persondrinks much water, his blood does not become diluted, because thekidneys become more active (or are "adapted," in respect to the goalG, to the momentary fluctuations in the blood's water contentcaused by the drinking), and the value of K increases. On the otherhand, if the body loses much water (for example, by sweating),water is released from the muscles and skin into the blood-stream,and M increases.10

However, for the process to count as goal-directed on the system-property view, it is not sufficient that on some given occasion (oreven on several occasions) the kidneys "just happen" to eliminateexcess water from the blood and so "happen" to keep constant theconcentration of water in it. An analogous observation has to bemade about the muscles and skin. To be goal-directed, the processmust satisfy the much stronger requirement that were the bloodinundated with water to a greater or lesser extent than was actuallythe case, the activity of the kidneys or of the muscles and skin wouldhave been appropriately modified. What this amounts to is that foreach member of a sequence of possible values (within certain limits)of the water content of the blood, there is a member of the sequenceof possible values of K, such that for each pair of these correspond-ing values the goal G would be achieved-that is, for each such pair,the water content of the blood would be 90 per cent. And similarlyfor the sequence of possible values of the water content of the blood,and the sequence of possible values of the variable M. It is evidentthat the process is both plastic and persistent; and it could also beshown that the relevant variables are orthogonal. The system istherefore goal-directed. It is also evident that being goal-directed isa property of a system, in virtue of the organization of its parts.Although in this example the goal is the product of a homeostaticmechanism, and only two variables were assumed to be relevant tothe realization of the goal, the analysis can easily be generalized to

9Sommerhoff,The Logic of the Living Brain (New York:Wiley, 1974),chu. .10Walter B. Cannon, The Wisdom of the Body (New York: Norton, 1939),ch. iv.


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274 THE JOURNAL OF PHILOSOPHYcover other types of goal-directedprocesses nvolving any numberof variables.But to do so would only complicate the discussion,without adding anything of importanceto what has alreadybeensaid. Moreover,since the system-propertyiew is intended to covergoal-directedbehavior whether it is biological or inanimate, it isnot relevant in an exposition of the view to discuss either the var-ious particulargoals that may be pursuedin thoseprocesses,or themechanismsoperative in them, or the origins of the mechanisms.Goal-directedprocesses n living systemsare patently programmed,containing"instructions"or the development(amongother things)of "feed-back"ubsystems;and the origins of the programsare leftto be explained by evolutionarytheory.A number of difficultieshave allegedlybeen found in the system-propertyaccount of goal-directed ystems.But the onlyreallyseriousdifficultyin that view with which I am familiar concerns the re-quirementthat the variablesrelevant to the realization of the goalof a processmust be orthogonal,in the sense alreadystated; and Iwant to examine this difficulty.Before I do so, however, I mustbrieflyexplain why this requirementis important: in short, it isthis requirementthat servesas a formalcriterion for distinguishingprocesses hataregoal-directed romthosewhich arecommonlyheldnot to be such.An example will help to clarify this claim. When a ball at restinside a hemisphericalbowl is displaced from its equilibrium posi-tion, restoringforcescome into play that in the end bring the ballto rest at its initial position. Is this a goal-directedprocess,whosegoal is therestorationof equilibrium?Were the processso classified,every process n which someequilibriumstateis restoredwould alsohave to be designatedas goal-directed;and in consequence, he des-ignation would be applicable to well nigh all processes, o that theconcept of being goal-directedwould not be differentiating,andwould therefore be superfluous.On purely "intuitive" grounds,however, the answer to the question just raised is negative-ananswerwhich is also in accordancewith the orthogonalityrequire-ment. For the controlling variables of the ball's motion are notindependentof each other, since the restoring force is proportionalto the magnitude of the displacement force, though oppositelydirected.-1 t seems, therefore, that the question whether a processis goal-directedcan be decided on the "objective"grounds stated

"1This example is discussed in Sommerhoff,Analytical Biology, p. 99. Anelementary mathematical analysis of an analogous problem is given in JohnCox, Mechanics(New York:Cambridge, 1923), pp. 210/1.


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GOAL-DIRECTED PROCESSES IN BIOLOGY 275in the requirement, rather than on the basis of "subjective" intui-tions that often vary from person to person.

But how are we to understand the requirement that the valueof a controlling variable at a given moment is independent of thevalue of any other controlling variable at the same moment? Onpain of contradiction, this surely cannot mean that the variablesmust be orthogonal in those very circumstances in which the sys-tem actually is in the goal-directed state relative to a given goal G.As the example of the homeostasis of the water content of bloodmakes plain, a system can be in a goal-directed state only if thereare determinate relations between the relevant variables. It is justbecause such relations hold that the variables cannot be completelyindependent of each other.12 What the requirement does mean isthat, apart from those situations in which determinate relationshold between the variables because of their role in goal-directedprocesses, the known (or assumed) "laws of nature" impose no re-strictions on the simultaneous values of the variables. For example,when the so-called "Watts governor" of a steam engine is nothitched up to the engine, any speed of the engine is compatiblewith any spread of the arms of the governor; for there are noknown laws of nature according to which, in the assumed circum-stances, the spread of the arms depends on the engine speed.

However, this presupposes that there are uncontroversial criteriafor distinguishing laws of nature from laws that hold only for var-ious specialized structures; and in any case, since the answer to thequestion whether variables are orthogonal depends on what lawsof nature are assumed to be known, the notion of being goal-di-rected is also relative to that assumption. Thus, on the system-property view, the system consisting of an engine with a governoris goal-directed with respect to the goal of a certain rotation speedof the engine's driving wheel. But if the relations holding betweenthe behavior of the governor and the engine speed were includedamong the laws of nature, that system could no longer be so char-acterized. Moreover, while the behavior of the simple pendulumis not goal-directed relative to the assumptions of Newtonian me-chanics and gravitational theory, before Newton's time that be-havior might very well have counted as goal-directed.

Is this relativization a fatal flaw in the system-property view? Ido not think it is. Although the answer to the question whethera given process is goal-directed is admittedly relative, in most cases

22 Woodfield,op. cit., pp. 67-72.


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276 THE JOURNAL OF PHILOSOPHYit is relative to factual assumptions which can, at least in principle,be tested empirically. The answer is therefore not necessarily sub-jective or unfounded. Indeed, it is frequently possible to decidebeyond reasonable doubt whether the variables relevant to a givengoal are orthogonal, at any rate within the limits of certainty re-quired in a given inquiry. For example, the two variables relevantto the analysis of a woodpecker's search for insect grubs on a treelimb, are the position of the bird's bill and the position of theinsect grubs; and these variables are clearly independent in therequired sense. Moreover, it does not seem to me to be a defect inan account of goal-directed behavior that it recognizes, whetherexplicitly or by implication, that assumptions of goal-directednessmay be mistaken and need to be corrected.

VTo provide explanations for the existence of various kinds of or-ganic structures and for the occurrence of different sorts of vitalprocesses, is an ongoing task of biology. I want therefore to con-clude this lecture with a discussion of some broad issues concern-ing the nature of explanations that are often proposed for, or inconnection with, goal-directed processes in biology.

(a) On the assumption that the system-property view is correct,if only in broad outline, the concept of being goal-directed can beexplicated without employing in the analysis any specifically bio-logical notions, and in particular without using any expressionsthat have a teleological connotation. This remark should not bemisunderstood. To say that a robin is hunting for worms in orderto feed its fledglings, is indeed a teleological explanation of therobin's behavior. However, the content of that statement can alsobe rendered by the assertion that the robin's behavior is goal-directed with respect to the goal of feeding its young; and thisassertion, since it does not contain such typically teleological ex-pression as 'in order to', neither is a teleological explanation noris it formally a teleological statement. Moreover, again on the as-sumption that the system-property view is sound, the assertion canbe explicated in such a way (whether or not the explication countsas a correct "translation" of the assertion) that terms like 'goal'and 'goal-directed', which have strong teleological overtones, donot occur in the explication.

This outcome is hardly surprising. For a major objective in de-veloping the system-property view was to analyze the concepts ofbeing a goal and being goal-directed so that the analytic versionsof these concepts would contain no undefined teleological notions.


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GOAL-DIRECTED PROCESSES IN BIOLOGY 277But on the hypothesis that this objective has been attained, expla-nations of goal-directed processes in biology are in principle pos-sible, whose structure is like the structure of explanations in thephysical sciences in which teleological notions have no place.(b) In the second place, explanations that have been proposed inconnection with goal-directed processes, account for the presence ofvarious items in two different ways. One such way is the explana-tion of how the goal (or outcome) of some goal-directed process orsystem is realized, in terms of assumed capacities of the system'svarious organs, the organization of the system's component parts,and a number of laws concerning the effects produced by the ac-tivities of those parts. For example, the homeostasis of the bloodtemperature in normal human beings would be explained in justthis way, if the statement that this temperature is approximatelyconstant were shown to be a consequence of assumptions whichassert, among other matters, that the body has glands whose activ-ity increases or decreases the body's metabolic rate; that moistureis evaporated in respiration and sweating; and that there are deter-minate relations, expressible as general laws, between these activ-ities and changes in the blood's temperature.Explanations of this sort are often said to be "causal." They re-semble in structure, though not in specific content, typical expla-nations in the physical sciences. As the example just consideredsuggests, they are like the latter in accounting for the occurrenceof some phenomenon by deriving the statement of its occurrencefrom assumed laws (or general hypotheses), when these are con-joined with statements of relevant initial conditions. Putting allthis briefly, one sort of explanation is in terms of antecedent con-ditions and causal laws; and goal-directed processes, among otherthings, can in principle be explained in this way. Explanations ofthis type are not distinctive of the life sciences, they are found inall branches of inquiry, and there is nothing teleological aboutthem.A second sort of explanation is characteristic of biology andother sciences that deal with purposive behavior. These explana-tions do not account for a phenomenon in terms of antecedentconditions and the mechanisms that produce it. On the contrary,they account, or seem to account, for the occurrence of a processor of some other item in terms of certain effects these things haveon the system of which they are members, or upon some othercomponents of the system. For example, if it is taken for grantedthat deer pursued by predators often survive by fleeing, explana-


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278 THE JOURNAL OF PHILOSOPHYtions of this second sort seem to account for the existence of var-ious items upon which the survival is contingent-such as theanatomical features of deer's limbs that make swift flight possible,or the keen sense of hearing of the animal-in terms of what thoseitems contribute to the survival of deer. Unlike explanations ofthe first type, those of this second type are often said to answerthe question why some process or organic structure exists, or whyit exists at just the place and time it occupies-in the sense of theparticle 'why' that requires mention of some purpose in the answer-by stating certain consequences of the process or structure. Suchexplanations have traditionally been called "teleological"; and itis beyond serious doubt that many biologists as well as philos-ophers construe them in the way just indicated.'3

Teleological explanations are the main concern of the secondlecture, and I am postponing until then further discussion of theirstructure. However, it has been recently argued by Professor RobertCummins 14 that it is a misconception to suppose that the only wayteleological explanations can be construed is as inferences fromeffects to causes-that is, as explanations of the existence of someentity in terms of certain effects the entity has in the system ofwhich it is a component. He rejects this customary interpretationof teleological explanations and proposes an alternative to it. Byway of constructing a bridge between the discussion of goal-di-rected processes in the present lecture and the issues to be exam-ined in the second one, I will conclude with some comments onthe first part of his essay.Cummins believes that if teleological explanations are inter-

preted in the customary manner, they face insuperable difficulties.What these difficulties are will be ignored for the present, thoughthey will occupy me in the second lecture. Nevertheless, it is be-cause of that belief that he presents a different reading of suchexplanations. The heart of Cummins's argument is that while hethinks it is "legitimate" to reason from effects to causes-for ex-ample, from the evaporation of water to its atomic constitution,or from the homeostasis of blood sugar to the secretion of insulinin the pancreas-the reasoning is said to be "a species of inferenceto the best explanation." For example, "our best explanation" ofthe constant water content of blood can be said to "require" kid-neys and muscles, so that presumably we can assert the existence

13 Cf. FranciscoAyala, "Biology as an Autonomous Science,"American Scien-tist, LVI (1968): 214.14 "Functional Analysis," this JOURNAL, LXXII, 20 (Nov. 20, 1975): 741-765.


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GOAL-DIRECTED PROCESSES IN BIOLOGY 279of these organs. "But once we see what makes the reasoning legit-imate," Cummins continues, "we see immediately that inference toan explanation has been mistaken for an explanation itself. Oncethis becomes clear, it becomes equally clear that [the assumptionthat to ascribe a goal to a process is to explain the presence of theitem characterized as having that goal] has matters reversed: giventhat [homeostasis of the water content of blood] is occurring in aparticular [organism], we may legitimately infer that [kidneys are]present in that [organism] precisely because [kidneys enter] intoour best (only) explanation of [that homeostasis]" (748).

Cummins is thus replacing an interpretation of teleological ex-planations that takes them to be explanations of the second type,by an interpretation that construes them to be explanations of thefirst type-though what is explained in the former case becomes afactor in what does the explaining in the latter. But how differentis the outcome when the replacement is made, from the outcomeprior to the replacement? On the customary reading of a teleologi-cal explanation, some effect such as the homeostasis of the bloodtemperature (call it E) is explained by assuming the operation ofsome cause such as the activity of various glands (call it C). On thereading Cummins proposes, the effect E is explained by assumingsome explanatory hypothesis (call it H) which is said to "require"the cause C (that is, the activity of various glands) that presumablymust be supposed to exist if the hypothesis is accepted as correct.In both cases, the existence of some item C is postulated (onCummins's proposal via the hypothesis H), whose activity is as-sumed to be at least a partial cause of the effect. But if this is so,the difficulties allegedly facing the customary reading of teleologi-cal explanations (according to which causes are held to be infer-able from their effects) are matched by difficulties no less seriousthat face Cummins's proposed interpretation (according to whichexplanatory hypotheses are supposedly inferable from effects de-ducible from them).However reasonable Cummins's proposal may be, it does notshow that the difficulties associated with the customary reading ofteleological explanations can be outflanked, by adopting a plau-sible interpretation for them that is free of comparable problems.A more extended examination of teleological explanations andtheir difficulties is therefore unavoidable. This is one of the tasksto be attempted in the second lecture.

NAGEL- Teleology Revisited

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