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Xavier Zubiri: Science, Nature, Reality


[Originally published in Faith & Reason, Vol. VI, No. 1 (Spring, 1980)]

Over the past several centuries, a battle between science and philosophy has been waged to determine which discipline opened the mind to a true perception of reality. It seems that the philosophers have largely lost, but Thomas B. Fowler suggests below that the problem has seldom been formulated properly, and that we must reexamine the whole notion of science's relation to reality in order to fully appreciate what science can and cannot do, and what the nature of human understanding really is. Fowler proceeds by summarizing the work of the Spanish philosopher of science Xavier Zubiri (1898­), who holds doctorates in theology and philosophy, and has studied physics, mathematics, biology, and history with some of the leading minds of the 20th century. Zubiri, who was professor of the History of Philosophy at the University of Madrid, is still writing and giving private courses.

When the author was an undergraduate, he chanced upon a remarkable bit of graffiti engraved onto a student desk:

And God said.

and there was light!

Humorous as this undoubtedly is, it nonetheless points directly to a complex of profound and exceedingly important questions: What are the relations among science, nature, God, and reality?

The proverbial man in the street knows that science investigates 'nature'; indeed, we speak of 'natural science' in contrast to, say, mathematical sciences. But specifically, the following questions need to be addressed: (1) What is the conception of nature required by science? (2) What is the idea of nature for everyday purposes? (3) To what extent can the nature investigated by science be regarded as synonymous with reality? (4) If reality is not exhausted by science, then what non­scientific reality is known to us, or knowable by us? (5) Is God's relation to reality that depicted above with the Maxwell equations, or is it some other? It is this complex of problems that Xavier Zubiri has sought to unravel, basing himself on the history of philosophy and the development of science, especially physical science in the twentieth century.


With respect to the first two questions, let us consider briefly the problem of physical laws. The scientist knows that physical processes are regulated by laws which are expressible in terms of mathematics. For example, under Newtonian mechanics the distance travelled by a freely falling body is s = 1/2 at2, What does this mean? Does the body somehow 'know' that it is supposed to fall in such a way that it satisfies the differential equation d2s/dt2 = g? Or consider the case of radioactive decay. In any given time period, a certain percentage of the atoms of a radioactive material will spontaneously decay. That percentage is constant as a function of the number of remaining atoms, and is totally independent of sample size. In fact, it is a universal constant for the material, and is usually expressed in the form of the material's half­life. But how do just the right number of atoms 'know' to disintegrate in a specified time interval? How does any one atom 'know' what its neighbors are doing? Is it some sort of Leibnizian pre­established harmony?

Or take what may be the most famous example of this apparent 'knowledge' on the part of physical objects. If we assemble the usual apparatus for measuring interference of electrons, consisting of a source of coherent (i.e. in phase) electrons having a wavelength given by the deBroglie relation , a screen containing two slits, and a second screen such that the electrons from the source passing through the two slits may impinge on it, we will observe an interference pattern. The exact details are unimportant. The phenomenon of interference is well­known, and occasions no surprise. But now let the electrons be emitted one at a time. We would expect, naturally, that the pattern should disappear, since it was formed only by the phase relationships resulting from large numbers of particles emerging from the two slits. But, when the experiment is performed, the pattern remains constant, in the sense that the electrons show up at the same places they did before. How can this be? How can one single electron go through both slits and interfere with itself? Or how can it know which point on the screen to strike? Yet somehow it apparently does. Or perhaps it doesn't. Perhaps the entire way of viewing the problem, which gives rise to this paradox, needs to be discarded.

In the first place, of course, we wish to be bound by the facts of nature, such as we know them(l). That is, no one wishes to deny that bodies fall with uniform acceleration, or that radioactive materials have a definite half­life, or that interference by single electrons is demonstrable. No one will deny these facts in order to save a view of science that may be outmoded. We do not accept the domination of empirical evidence by a priori notions, as, for instance, does Hegel with his famous "So much the worse for the facts if they do not conform to the laws."(2) On the other hand, we cannot attribute intelligence to nature; in the words of Weizsacker: "Nature is not subjectively spiritual; it does not think mathematically. But it is objectively spiritual; it can be thought mathematically."(3) But does 'thought mathematically' mean that science investigates real things such as chairs, men, animals, and the like such as they are given to us in our experience of living? This attitude, apparently so self­evident and unquestionable, nonetheless gives rise to serious problems, as we have seen above. Are we compelled to assume that reality is delivered to us in science, and that science tells us what there is to know about things, while our ordinary experience of them is only an approximation to this truth? Similiarly, are we compelled to attribute our usual notions of causality to the objects physics investigates? Is it not this which has led us directly to the above paradoxes, e.g., wondering what 'caused' each atom of the radioactive material to disintegrate or not do so; or what 'caused' the electron to interfere with itself? Is the concept of nature univocal in that sense? No, according to Zubiri: is not true that the idea of nature, in the physical sense, is the idea of the nature of things simpliciter. In fact, Galileo's great work consisted in distinguishing these two ideas and attempting to give physical sense to physics. This task had been fully prepared in the ontology of Duns Scotus and Ockham, but was only realized explicitly and in mature form in the work of the Pisan thinker. For Galileo there is a radical distinction between nature in the sense of nature of things and nature in the sense of physics; and analogously, a distinction between causality as an ontological relation, and physical causality.(4)

Physical causality, for Galileo, is concerned only with variations-Hume's constant conjunction-whereas causality in the ontological sense seeks to discern the origin of the being or existence of things. This critical distinction has served well, to the degree that something which does not vary at all for the purposes of our experience has no physical meaning. An example is the famous hypothesis that the universe is characterized by some uniform rectilinear motion, which was finally put to rest by Einstein. In Zubiri's words: "Physics cannot occupy itself with the origin of things, but only with the measurement of their variation; it is not an etiology, but a dynamics."(5)

But what, then, does physics investigate? The answer is that it seeks to measure (in the most general sense) phenomena. What is a phenomenon? What does science understand by it? A phenomenon is something perfectly real which appears in the course of our experience, inasmuch as it appears; for instance rain, the falling of bodies, temperature variations, and so forth. The connection with science is immediate:

When phenomena are thus understood as real happenings, science proposes to determine when, how, and why they appear. It seeks to circumscribe with the greatest possible precision the temporal and spatial arena of their apparition, and for this it preferentially employs some type of measurement.(6)

Note carefully that every phenomenon, though it is an object of science, makes an essential allusion to an observer before which or whom it appears. Without that observer, the phenomenon would have real existence, but not an appearing: "Nature is, in this sense, a spectacle; 'spectacle of nature' is the best translation of 'scientific phenomenon'. As such, it involves inevitable reference to a spectator, real or imaginary. This reference is what makes a reality be a phenomenon."(7) So according to Zubiri, the sense of the expression 'phenomenon' is that of an aspect of nature, and hence not a thing, as it was for the Greeks, but a happening, an event. We will understand this happening only when we know its place in the course of nature, i.e. in the overall sequence of phenomena. And that we obtain by measurement. Thus the origin of modern physics is traceable to measurement of the variations of phenomena.(8)

This implies a change in our usual view of physics as knowledge of the world, because the objects of physics are no longer to be regarded from the point of view of being; that is, they are not entities in the metaphysical sense, but simple phenomena, i.e. manifestations of what already exists or is, in the same way that movement is a simple variation of what is:

The phenomena of nature are not the things of the world. Hence, concepts of mass, material, etc. which up to now have been assimilated to the idea of thing, henceforth signify something different. They correspond to different problems. Mass, for example, is nothing more than the quotient of force by acceleration, and so forth. But just as variation neither excludes nor includes causality, phenomenon neither includes nor excludes entity in the sense of thing.(9)

In short, the problem of nature, for Galileo and all of modern science, is not the traditional problem of entity and causality in the strict sense. And this immediately brings up the question of the relationship existing between phenomena and the objects of physics, since we are rejecting the notion that physics studies the things of the world simpliciter. According to Zubiri, phenomena cannot be regarded as approximations to any ideal objects of physics, but rather are themselves those very objects. Hence the words 'atom', 'electron', and so forth, lose their old meaning of absolute ideal objects and become words designating systems of phenomenological relations. Hence,

...when contemporary physics speaks of the equivalence between waves and particles, it does not imply that material things soften and become diluted in some vague and formless reality; but that this equivalence is, in fact, a purely phenomenal equivalence. The concepts of particle and wave are interpretations of observables. For this physics does not have to take leave of observables and substitute objects of thought for them. The new physics does not substitute some beings for others.(10)

Similiarly, a scientific law, expressed mathematically, no longer has the metaphysical significance of determination of some absolute reality; rather, such a law

...has no meaning other than that of being a conjunction of virtual observations; is the probability of an observation, not the real determination of a state. Or in other words, for physics the real state of something is only that in which I see it.(11)

But how does this apply to the problems we discussed above? Consider the case of the radioactive material. This material is, for the purposes of science, nothing more or less than a group of phenomenological relations, upon whose appearance we can place no a priori restrictions. Thus, the observed half­life is simply a phenomenon; given the material, after a certain time, we can measure that only half of it remains undecayed. Given one observation (the material), we will subsequently have another (half of it is gone). That is all the scientist qua scientist really cares about starting with observation x at time t1, he will observe y at time t2. Thus with the electron: we start with one set of phenomenological relations, viz. the electron source, screen, etc., and end up with a second: the interference pattern. That is all science is concerned with: the structure of the phenomenological relations in the broadest sense, including (and especially) their temporal succession.

Briefly, then, the nature with which science is concerned is that of phenomena, i.e. what appears and can be measured, and for which temporal succession can be established. The nature of our everyday experience, i.e. the things of the world, is not what science qua science investigates.


Let us now turn to the third question, viz. to what extent can the nature investigated by science be considered synonymous with reality. Zubiri summarizes the situation as follows:

During the modern era, since about 1700, man has lived so persuaded that reality is discovered to him by science that nothing seems able to make him even notice the existence of this basic persuasion. For him, there is no room for the least doubt about it. Perhaps science happens to be somewhat fragmentary and changeable; but modern man sees in these two characteristics something more than a sad human condition: he has elevated them to the category of formal structure of science, and has thus made science a constitutive approximation to reality.(12)

This enthronement of science has extremely profound consequences, for it implies that "...everything there is in reality which is accessible to man, has to be so in a way eminently scientific."(13) Zubiri attributes this rise of scientism not so much to rationalism or to any positivistic critique of knowledge, but rather to the profound conviction that has grown in Western Civilization that through science man attains the only parcel of reality which is accessible to him with certainty. There have been attempts to gauge the scope of science, ranging from a prudent 'partialism' in our conquest of reality ('only a portion of reality is accessible to us; we can never know everything about anything'), to a pragmatist symbolism ('science has nothing to do with reality, but only with human necessities; it is strictly a group of conventions useful for the manipulation of things'). Yet there is something in common: the bottom of all these attitudes lies the profound conviction that the fate of reality accessible to us depends ultimately upon the fate of science, at least in respect of intellectual apprehension. And if in fact man has any other contact with reality, it would have to be through some sort of irrational intuition.(14)

Indeed, the common belief is that science has finally provided us with a method for reaching the goal long ago set by Aristotle, viz. knowledge of the world, or reality: "But if one inquires about what should be understood by 'science', regardless of the specific reply given, emphasis is always on the science, in the singular, as a univocal effort to intellectually conquer the reality of things".(15) Zubiri notes that when, after about the year 1500, the Nuova Scienza arose and modern thought began its offensive against Aristotelian knowledge, the methodology of the new science was presented above all as a critique of Aristotle's syllogistic, as a derogation of Aristotelian science, and most importantly, as a new substitute for it. But the novelty affected only method and content, not the intellectual intent itself.(16) In other words, Aristotle's goal remained unchanged; only his methods (i. e. philosophy) were deemed inadequate for the task, to be supplanted by the modern tools of experimental science:

Everything seems, then, to lead us to the idea that what the Greeks called episteme signifies the same thing which we call 'science', and that the great work of modern science has consisted in showing the falsity or at least poverty of Aristotelian 'science', while at the same time giving man a new method for reaching the same goal. Although variously realized, and with different results in different moments of its history, science is thus always a univocal force directed toward intellectual conquering of the reality of things.(17)

Zubiri's criticism of this general position is twofold. First, internal to science itself, there have been developments during the twentieth century rendering it untenable; and second, externally, science and philosophy have different objectives which male any such assimilation impossible.

The developments of interest in physical science center on Heisenberg's Uncertainty Principle, which deals with the question of measurement, and the relation of that principle to determinism and causality. Causality is a deeply intuitive notion founded on experience, the experience that events do not happen capriciously; rather, one event, such as throwing a stone, causes another, such as breaking a window. Determinism, or strict determinism, is the theory that all events or happenings in the world are strictly determined in every possible detail by physical laws, and that there are ultimately no chance or random happenings (and a fortiori no free will).

Consider first the significance of measurement in classical physics:

With the concept of quantity in classical physics it is clear that mathematical formulae lead from an initial quantity to a final quantity or quantities which are real; i.e. if we carry out measurements on the final state, the results will approximate more or less the true value of the quantity measured.(18)

This contrasts sharply with the notions of quantum mechanics, in which the Uncertainty Principle affirms that one cannot measure what are referred to as conjugate quantities with arbitrary accuracy. Rather, there will always be a degree of uncertainty in the measurement of each, such that the product of the uncertainties is greater than a fixed number called Planck's constant. For example, in the case of position (x) and momentum (p): .

The existence of this principle forever precludes from realization the goal long sought after by science, that of being able to predict with arbitrary accuracy the entire future or past course of the universe (or any part of it), once sufficient information about the present is known. It precludes it in the sense that henceforth such a goal has no physical meaning. Thus it clearly points up the metaphysical and non­scientific nature of the goal, because it does not say that the universe is not strictly determinate; but only that such strict determinism (if it is real) is not part of the nature which physics examines. One can go on maintaining determinism, but must realize that it is a metaphysical hypothesis about reality which has no basis in physical science. Indeed, it is possible that things may be related by determinate links, in the sense that the state of an electron at some instant univocally determines its entire future course. But as Zubiri points out,

...what Heisenberg's principle affirms is that such a determination has no physical meaning, on account of the impossibility of knowing exactly the initial state. If this impossibility were accidental, i.e. if it depended on the subtlety of our means of observation, Planck would be right. But if it is an absolute impossibility for physics, i.e. if it is founded in the very nature of measurement as such, the presumed real determinism escapes physics. It no longer has physical meaning.(19)

That is, a scientist cannot, even theoretically, make any sequence of measurements which would confirm the supposed determinate links. And in that case,

...the Uncertainty Principle would not necessarily be a renunciation of the idea of a cause, but rather of the idea that classical physics formed of causality. This, and nothing more, is the scope of the Uncertainty Principle. It is not a statement about things in general, but rather about things as objects of physics.(20)

Note carefully that if what cannot in principle be observed must be regarded as not having physical reality or physical meaning, then much of what heretofore has been considered as 'really' happening and 'really' caused must be abandoned. That is, not everything can be regarded as 'caused' in a physical (i.e. observable) sense:

Be as it may the real activity of each molecule, from the moment it is unobservable, it lacks physical meaning. Physical laws are nothing but anticipations of experience, i.e. effective measured values, realized or realizable within the bounds of observation. Therefore nothing has physical meaning other than that approximation which is really accessible to observation.(21)

Whence physical laws, because they deal only with mean values of observations, rather than some hypothetical 'absolute' value, give only the distribution of these values; i.e. they are statistical rather than deterministic laws, and,

...the reality measured by the value of practical approximations is not something independent of our observations, but rather the statistical limit of : . . .' classical physics the electron is at a place which perhaps I do not see, but which I believe has to exist. For the new physics the electron is where it can be found.(22)

This situation caused a great deal of mental anguish on the part of the theoretical physicists, because it seemed to entail a complete rejection of the intuitive notions of causality, which, despite Hume, many felt were at the very heart of scientific explanation:

Uncertainty or indeterminism seems to be what is most opposed to the character of all scientific thinking. Planck, therefore, indignantly rejects this concept; to renounce determinism would be to renounce causality, and with it, everything that has constituted the meaning of science from Galileo up to the present day.... Indeterminism, if it exists, would be for PlanckPlan a characteristic of the present state of our science, but in no way a characteristic of things themselves.(23)

Why were the physicists, together with many others, so disturbed? The answer is simple. If the notion of strict determinism has to be abandoned because of developments internal to science itself, then the equation (assumed implicitly by scientists from the renaissance to the 20th century):

causality = determinism = regulation of all reality by physical laws

has been dealt a shattering blow, and with it the two related equations:

science = knowledge

field of scientific investigation = reality

These latter two, indeed, are tenable at best only on the assumption that anything one wishes to know about the perceivable world can be determined with arbitrary accuracy by science.

The splitting of causality, determinism, and physical laws entails a radical rethinking of the nature of science as a human enterprise and as well of the three notions themselves. First, physics can no longer be regarded as capable of telling all there is to know about happenings in the world. As Zubiri has keenly observed:

...not only is it untrue that the idea of cause gave rise to modern science, but in fact modern science had its origin in the exquisite care with which it restricted this idea. That renunciation was for the representatives of the old physics the great scandal of the epoch. How is it possible for physics to renounce explanation of the origin of all movement? This heroic renunciation, nonetheless, engendered modern physics.(24)

What can we say about physics vis­a­vis reality as a whole? Consider what happens when one sets out to do physics. As an experimental science, physics is directed to natural things-in contrast, say, to supernatural things. Moreover, it begins not when we deal simply with things, even if they are corporeal, as we have noted above. Rather, physics begins when we make the meaning of the adjective 'natural' precise.(25) What do we understand by 'natural'? What is 'nature'? Clearly, "An answer to these questions has to be an affirmation that will mark off, within the world of what there is, those entities which fall within the region of the natural."(26) That affirmation has been hammered out over the last four centuries, and finally appears to have attained its mature form: "The cardinal difference which makes a being, besides existing, to be natural, is not that its movement is caused in a certain way, but that it is determined as phenomenon, i.e. measured in the course of nature: nature = measure of a course = phenomenal law." (27) Second, with respect to causality, we can say that the Uncertainty Principle has led to clarification of the notion of causality as a metaphysical principle, because it has shown that 'causes' in the traditional sense are not part of physics. Physics restricts itself to determining the variations in phenomenological quantities, rather than seeking to determine the origin of things or movement:

...this does not mean that the Aristotelian concept [of causality] has been abandoned, only that it answers another problem, viz. the problem of being in general. It is possible to interpret determinism as causality, admitting that causes act determinately. But even so, it would not do us any good, not because causes are not real, but because they have no physical meaning.(28)

And finally, determinism, so beloved of scientists for so many centuries, not only must be rejected for the purposes of science, but indeed cannot be regarded as equivalent to causality either, so that by purging science of notions of determinism we do not thereby renounce causality:

But neither is the Uncertainty Principle a principle of ontology in general, as if it pretended to deny the existence of causality. Whatever may be the verdict on that, it does not affect the Uncertainty Principle at all. Causality is not synonymous with determinism; rather, determinism is a type of causality. (29)

Determinism is a metaphysical hypothesis about the universe which may or may not be true. But however the universe may be determinate, it is not so in any way which can be given scientific meaning or verified scientifically; hence, the notion of determinism is not required for the conduct of science.

To summarize, the Uncertainty Principle has made the nature of physical knowledge much clearer, and shown that science cannot be regarded as synonymous with knowledge in general because it deals with a portion of reality only and does not, indeed cannot, explain all change and all happenings in the world. Hence the notion of a strictly determinate universe in which everything is predictable, even theoretically, on the basis of physical laws, and for which metaphysical knowledge is thereby rendered superfluous or outmoded, has to be definitively rejected.


Turning now to Zubiri's second criticism of the univocal view of human knowledge, we may note that he believes there is a difference between the objects and goals of philosophy and science; and he explains this difference in terms of the notions cosmos and world. We have already had occasion to remark on the difference between the phenomena of science and the things of the world; but this distinction is ultimately only part of a much larger and more profound one, that between cosmos (as ordered totality of things) and world (as comprehensive scheme of phenomena). Knowledge about the cosmos, which means knowledge of the things constituting it-men, plants, the sea, etc.-is the object of Greek episteme physica; whereas knowledge of the regular appearances of phenomena is the goal of modern science. The connection, so to speak, is that phenomena manifest what things are.(30) This general position becomes clearer when we consider the attitude taken by the Greek vis­a­vis that taken by contemporary man in his experimental science:

Face to face with phenomena, the Greek immediately directed his attention to the things which appeared. He did not know how to extract what is called 'world' from this subtle structure which he possessed, the world which man has and in which he exists. Science has determined that the passing of phenomena obeys laws and not just causes, i.e. that phenomena constitute a world characterized by its own proper structure, a world which consists in its own occurrence or happening.(31)

It is not true, of course, that the Greek failed to recognize that what we have termed 'world' exists; rather, it held little interest for him, and he preferentially directed his attention to the things of the world. If he was interested in structures, it was the structures of things, not of phenomena. Science, on the other hand, bases itself on the idea that phenomena constitute a world. But the Greek did not regard the universe as a chaotic conjunction of entities or things; recall Aristotle's taxis of the physical world which culminates in the Theos. Rather, through the four causes, the movement of all things in the universe was to be explained, ultimately with reference to the Theos. Science, on the other hand, restricts its attention to the world and the phenomena occurring therein.(32)

Zubiri's position may be summarized briefly as follows, using his own words: "Science tries to ascertain where, when, and how phenomena appear. Episteme tries to ascertain what things must be which are thus manifested in the world."(33) With respect to the notion of causality, for instance, Zubiri has very succinctly noted the difference:

For science, a force acts on account of its own proper nature, uniformly. A scientific study of force is only complete when the conditions under which it appears and the way in which it acts are univocally determined. That is, one must determine a conjunction of manifestations which follow other earlier ones. Only when the former are found necessarily linked to the latter can we properly speak of scientific knowledge. In other words, precise formulation of the uniformity in nature's actions is the goal science pursues; this is the lex, law. But in terms of causes, this uniformity, this law, is not an object but the very problem: How must things be so that they act uniformly?(34)

It is episteme which represents the origin of philosophy, and of which philosophy today is the heir and continuation. Our desire to know about the things of the world as realities is knowledge in the manner of episteme. Science, which to some degree had its origin in a 'desire to know about the world,' is not the logical development of episteme or the 'true' heir to it; rather, science is a different type of knowledge about the world, which does not supplant philosophy or render it useless and outmoded. In short, our knowledge of the world is not univocal in the sense that modern science now gives us a true version of what, in earlier times, philosophy haltingly sought to determine.

And this brings us to the last two questions. Consider our perception of reality. Any philosophy must, before all else, come to grips with and be compatible with our most basic experience. And for Zubiri that experience is not of ideas, or concepts, but of reality itself: the world, other men, trees, and the like. As he puts it:

...there is something which is antecedent to exercise of the intellectual function: things themselves must be 'put­before' the understanding; that is, things have to be present to man. We leave aside any subsequent complications. Whatever may be the means and ways by which man can have things present, they have to be there. Otherwise it would be impossible to even begin to understand....And to this patency of things the name 'truth' can be given in the most fundamental sense.(35)

This question is closely related to another one, the celebrated problem of the existence of the external world. For empiricists, who enclose themselves in their own 'ideas', the 'external world' becomes problematic in the sense that we can never know it, only our own ideas, which may or may not be an accurate representation of it. The external world may exist, or it may not: we cannot know. Thus the scientist, as we have seen, ultimately concerns himself only with phenomenological laws; he does not need the supposition of some 'real' external world, which at best would be something 'added' to him as subject. But:

Is it true that the existence of the exterior world is something 'added'? Is it true that it is a simple fact, including whatever one may wish, but when all is said and done, still a fact, nothing more?...We have already seen how the being of the subject consists formally, in one of its dimensions, in lying 'open' to things. Accordingly, it is not that the subject exists and, 'besides' him, there are things; but rather that being a subject 'consists' in being open to things. The exteriority of the world is not a simple factum, but rather the formal ontological structure of the human subject, in virtue of which there could be things without men, but not men without things.(36)

According to Zubiri, this state of affairs does not have its origin in some sort of necessity founded on the principle of causality; nor is it traceable to any logical contradiction implied in the concept of man. Rather, it is owing to "something more: because it would be a type of contra­being, or human contra­existence....Without things, then, man would be nothing. In this his constitutive ontological nihility, there is implied the reality of things. Only then is there sense in asking in an individual case if each thing is real or is not real."(37)

But what does this mean with respect to reality as a whole? Is science by itself capable of delivering reality to us? No; and the proof is in our most basic experience:

To physics, freedom, for example, has no meaning; not because it isn't real, but because its reality has no physical meaning, or as it were the meaning which physics gives to the word 'reality' leaves the fact of freedom outside of the world. But this, of course, does not prevent freedom from being a fact nonetheless, i.e. a reality, though in a different sense than that which physics assigns. The idea of reality acquires its meaning through the 'all' in which each real thing is inscribed.(38)

And what is more, physics after quantum mechanics no longer has the meaning of investigation of absolute space and time, of reality in an ultimate sense, the sense which gave rise to the so­called scientific proofs of the existence of God, based on such things as Fermat's principle of least time, or the second law of thermodynamics. Indeed, "Physics, even more than in the case of Einstein, has nothing more than a human meaning. Strictly speaking, for God not only is there no physics, there is no Nature in this sense, either."(39)

Can we then give a more comprehensive definition of reality? One which will not do violence to any aspect of our experience? "Reality is all and only that which acts upon things or upon itself in virtue, formally, of the characteristics which it possesses."(40) Obviously free will, God, and other immaterial things can act on men. They do not act in the phenomenological sense, but they are not therefore unreal. Indeed, they are more real, so to speak, than the phenomena so widely hailed and upon whose understanding and manipulation this world is staling its salvation.

Now this does not mean that cosmos and world are somehow separate realms which just happen to coincide in certain respects, e.g. the laws of physics and chemistry regulating and controlling the way things of the world behave, as if we were dealing with some form of Leibnizian pre­established harmony or Malebranchian voluntarism. Rather, the case is that our primary experience is that of perceiving reality, and science can, at best, allow us to have more experiences (in the sense of a broader range) and thus perceive more of reality; but in itself it is not capable of giving reality to us. Reality is, to paraphrase the medieval expression, the formal object of the human understanding, in a totally irreducible sense. Viewing science as an effort to manipulate and control the phenomenological world, we can say that even animals do that; and certainly machines can be built to do it. But machines can never be built which will understand truth or perceive reality. Phenomena simply manifest to a certain degree the behavior of the things of the world. Science is not ontology; and the phenomenological world is not ultimate reality, but simply a field for moral action. In Zubiri's words, "We must know if philosophy and the being of man are going to nourish themselves, ultimately, on what 'goes on in the world' or on what things and men 'are in reality"'.(41)


Zubiri's theory of science and knowledge can perhaps best be summarized by considering his view of the historical development of science and philosophy. According to him, rational knowledge began, in Greece, as an effort to understand and explain the cosmos, taken to be the sum total of the things of the world. While understanding was the primary goal, use of the knowledge gained for control of the world was implicit. This conception reached its maturity in the work of Aristotle, for whom knowledge of the world was a knowledge of things through the four causes. Nature was identified with the cosmos, and there was no clear distinction between scientific knowledge and philosophical knowledge as we understand those two. The development of experimental science in the late medieval and renaissance periods led to a different view of nature, identified now with phenomena, and understood by most as replacing the Aristotelian view, which was deemed inadequate for supplying knowledge of the world. But that knowledge of the world was still regarded as the unique goal. Phenomena and things were supposed to be capturable through laws in a complete and fully deterministic way, to the extent that all change in the perceivable world was explainable on the basis of these laws (Laplace's demon).

The triumph of this modern scientific view over Aristotelian science with respect to controlling phenomena was complete, and was taken to mean that philosophical knowledge had largely been superceded. The development of quantum mechanics shattered this picture, but less because it led to a new view of nature, as being systems of observables, as because it entailed renunciation of the notion- dogma rather-of completely deterministic causal nature and thus the ability of science to forecast the course of all events with arbitrary accuracy. The univocal view of human knowledge was dealt a severe blow, and the epistemological and metaphysical implications of science and scientific knowledge were significantly altered. The fact that science was clearly seen to be concerned with dynamics and not etiology, that there is a distinction between nature in the sense of physics and nature in the sense of things simpliciter, that there is a distinction between physical causality and causality as an ontological relation, and that science can at best give a probability distribution of observables rather than arbitrarily accurate predictions of events, has led to a notable clarification of the relation between science and knowledge in general, and in particular of the restricted scope of science vis­a­vis human experience as a whole.

The answers to the original questions may be summarized briefly as well:

(1) Nature for science is phenomena, and the things of nature (atoms, etc.) are systems of phenomenological relations whose behavior is described by laws without reference to causality in the traditional sense.

(2) Our ordinary perception of nature is that of things as realities, linked by causes and forming a cosmos; the phenomena we experience are only means to that end, which is prior both epistemologically and metaphysically.

(3) The phenomena investigated by science cannot be regarded as synonymous with reality simply because reality is perceived in a way prior to science. That is, a person, in the technical theological sense, has the capability of perceiving reality through phenomenological experience; but the phenomena themselves are not reality; they are just that: phenomena.

(4) Our most basic experience is of non­scientific realities: other persons, free will, things as realities, colors, sounds, beauty, and so forth. The equation of the real and the scientifically knowable, so uncritically accepted today, must be rejected for this reason.

(5) Since the world does not exist in time for God, there is no 'physics' for Him; so He cannot meaningfully be regarded as having created the world by any sort of fiat expressing Maxwell's equations, the deBroglie relation, Schrodinger's equation, or others. Nor does the world exist as nature in the sense of phenomena for God; nature is only the way we as men perceive it.


1 We prescind from the question of whether there are any facts separate from theory, at least for scientific purposes.

2 Quoted in Wolfgang Strobl, La Realidad Clentifica y su Critica Filosofica, Pamplona: Universidad de Navarra, 1966, p. 103.

3 Weizsacker, quoted in Strobl, op. cit., p. 113.

4 Xavier Zubiri, Naturaleza, Historia, Dios, sixth edition, Madrid: Editora Nacional, 1974, p. 288­289 (All quotations in English are from the present author's forthcoming translation; page numbers are for the Spanish edition, however).

5 Ibid., p. 289.

6 Ibid., p. 73.

7 Ibid., p. 73­74.

8 Ibid.

9 Ibid., p. 295­96.

10 Ibid., p. 302.

11 Ibid.

12 Ibid., p. 63.

13 Ibid.

14 Ibid., p. 64.

15 Ibid.

16 Ibid.

17 Ibid., p. 64­65.

18 Ibid., p. 283.

19 Ibid., p. 288.

20 Ibid.

21 Ibid., p. 283.

22 Ibid., p. 284.

23 Ibid., p. 287.

24 Ibid., p. 289.

25 Ibid., p. 290.

26 Ibid.

27 Ibid, p. 296.

28 Ibid., p. 295.

29 Ibid., p. 291.

30 Ibid., p. 87­88.

31 Ibid., p. 88.

32 Ibid.

33 Ibid., p. 78.

34 Ibid., p. 76­77.

35 Ibid., p. 13.

36 Ibid., p. 365.

37 Ibid.

38 Ibid, p. 89.

39 Ibid., p. 302.

40 Xavier Zubiri, Sobre La Escencia, Madrid: Sociedad de Estudios y Publicaciones, 1963. p. 104 (author's translation).

41 Zubiri, Naturaleza, Historia, Dios, op. cit., p. 95.