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 This article was originally contained in The Maritain Volume of The Thomist published in January 1943 as volume V of The Thomist (New York: Sheed and Ward, 1943), pp. 85-102. The collection was occasioned by Jacques Maritain’s sixtieth birthday. We thank the publisher for granting us permission to republish it in our Thomas International website.





Yves Simon



THE MEN engaged in the Thomistic revival which began late in the nineteenth century soon had to face this challenge: Because the philosophical principles of Thomism were established at a time when positive science was in its infancy, it seemed that Thomism was forbidden ever to deal successfully with the problems of our time. There could be no provision in the system of St. Thomas for the interpretation of either the results or the spirit of modern science, both of which influence so deeply the very statement of our philosophical problems. The collapse of Aristotelian physics had entailed the general ruin of the Thomistic philosophy; against this verdict, rendered at the time of Galileo and Descartes, there could be no appeal. Thomism was at best a remarkable phase in the development of Western thought. If something of it could be revived, it was a certain inspiration, a certain aspiration, a certain frame of mind, but not any part of the systematic synthesis actually known under the name of Thomism.

Such was the only possible attitude for those who held that no part of philosophy is independent of positive science. More moderate persons were willing to make an exception for metaphysics, considering that our knowledge of the one, the true, and the good is little affected by what happens in physics and mathematics. But with regard to cosmology, psychology and even logic, the restoration of a philosophy conceived in the middle ages was deemed plainly impossible. The result was a number of eclectic constructions in which St. Thomas was permitted to supply a few general truths but not any refined and detailed achievement.

As a matter of fact, in order to know how far Thomism was affected by modern developments in the positive sciences, a group of preliminary questions had to be examined. Has philosophy a distinct object? Is philosophy a science or not? One science or several? What is the significance of the distinction between philosophical and positive knowledge? Is it a necessary and everlastingly indispensable distinction, or a merely provisional one? What about the kind of truth that belongs to philosophy? To positive knowledge? Is it the same or not? All these questions were profoundly worked out in the critical research whose climax was the publication, in 1932, of The Degrees of Knowledge.[1]

The pioneers of the Thomistic revival had rather vague ideas about the nature of the disciplines which some of them practiced with great ability. It seems that they were not particularly interested in problems pertaining to the specification of philosophical sciences. Today we consider it a paradox that Thomists ever accepted a division of philosophy which was initiated by Wolff, popularized by Kant and the eclectics of the school of Cousin, and which was fundamentally at variance with that upheld by St. Thomas. Our old masters undertook the restoration of Thomistic philosophy without having asked themselves what conception of philosophy and of its divisions a philosophy must adopt in order to be consistently Thomistic. Maritain has carried out, with uncompromising firmness, the task of rediscovering and reasserting the genuinely Thomistic concept of philosophy.

It is now currently known that the whole doctrine of St. Thomas concerning the theory of science and philosophy is commanded by the distinction of three orders of theoretical abstraction. In an early treatise, the Expositio Super Boetium De Trinitate, St. Thomas develops, explains and justifies the tripartite division of knowledge which had been outlined by Aristotle. Some objects are such that they can neither exist nor be understood without matter, i.e., apart from the principle which makes things both perishable and observable. Others are such that they can be understood without any reference to sense qualities and the principles of mobility, although they cannot exist except in corruptible and observable subjects. Finally, some theoretical objects are determined by such a law of abstraction that they can both be understood and exist apart from matter. The general division of theoretical knowledge based upon the consideration of the orders of abstraction is most profoundly objective, since it proceeds from the characteristics of the scientific object as such. Theoretical knowledge is primarily divided into physics, mathematics, and metaphysics.

This primary division which is the indispensable foundation of all Thomistic speculation about science and philosophy was strangely disregarded by the Thomists of the nineteenth century. Following divisions set up by Wolff, their metaphysics is divided into a general metaphysics, and a special metaphysics, itself divided into three disciplines: cosmology, psychology, natural theology (the last being designated, to make things worse, by the absurd term "theodicy"). Such a conception radically upsets concepts which play an essential role in the Thomistic synthesis. Considering the philosophy of the world (cosmology) and the philosophy of the soul (psychology) as parts of metaphysics is, from a Thomistic point of view, completely nonsensical; for the whole observable world, including the human soul which is the form of a perishable body, belongs to the order of objects which can neither exist nor be understood apart from matter.

Maritain has done much to restore the concept of philosophy of nature. Badly discredited in the nineteenth century by the romantic Nature‑philosophie, this concept had never been satisfactorily defined, inasmuch as the disciples of Aristotle never succeeded in distinguishing clearly philosophy of nature from positive science. St. Thomas uses synonymously the expressions Philosophia Naturalis, Scientia Naturalis, Physica. The problem is whether there is room within the first order of abstraction for more than one approach to the physical world.

In this connection, the Thomistic tradition includes possibilities of which the Thomists themselves were not sufficiently aware. Each order of abstraction admits of inner Thomas, whom Maritain knows so well and loves so dearly, John of St. Thomas, points out with his usual clarity that within one and the same order, various degrees of abstraction determine so many distinct sciences. For instance, within the second order the Thomists distinguish the degree of abstraction proper to geometry and the higher degree proper to arithmetic. Within the third order three degrees and correspondingly three sciences are distinguished: logic, metaphysics, and theology. John of St. Thomas explains that the abstraction which defines an order is an initial one and consists in the disregarding of some sort of material data: individual matter in physics, sensible matter in mathematics, all matter in metaphysics. Once this initial abstraction is effected, the mind has entered into an order of intelligibility which should not be likened to a plane but rather to a space. For within this realm of intelligibility the mind still enjoys the freedom of moving up and down in such a way as to reach various degrees of terminal abstraction.

Ancient scholastics had only vague hints of the inner differentiation of the first order of abstraction. Applying to the first order the principles which had satisfactorily accounted for the inner differentiation of the second and third was to be attempted. Maritain restored and purified the Thomistic concept of a philosophy of nature by elaborating on an undeveloped aspect of historical Thomism.

Every representation concerning the observable world shows a dualistic or bipolar character inasmuch as it refers to an intelligible objects pressing itself through a stream of sense appearances, and to a stream of sense appearances stabilized by a center of intelligibility. This bipolar character of the physical object and its representation is clearly suggested by the traditional definition of physics as the science of the ens mobiles eu sensibile. The physical object is both intelligible (ens) and observable (mobile seu sensibile). Neither of these opposite characteristics can be disregarded without its specific nature being destroyed. Leave out the words mobile seu sensibile and we are no longer dealing with something physical. Leave out the word ens and we fall below the level of intellectual knowledge.

Yet physical thinking, while bound to adhere to the two aspects of its object, can put a particular emphasis on one of them. If the emphasis is put on ens, we have a form of knowledge both ontological and physical, a philosophical physics, a philosophy of nature. If the emphasis is put on mobile seu sensibile, we have a discipline of a physical and non‑ontological character, an empiriological science. This point must be insisted upon: the privilege granted to either pole of the matter of emphasis. The philosopher of nature is not a metaphysician, and his definitions must imply some reference to data of sense experience. On the other hand, the empiriologist is not a mere dealer in sense experiences, for the observable regularities with which he deals owe their constancy and their consistency to their being organized by some ratio entis. In this connection it is fitting to stress the felicitous character of this newly coined expression, empiriological sciences. Speaking of empirical sciences is objectionable, though customary, since empiricism is said in contradistinction to scientific knowledge. Empiriological sciences are not mere empiricism, but a system of experience organized by an essential reference to a principle of intelligibility.

How physical thinking organizes itself around either pole of its object can be best evidenced by investigating the way physical definitions are constructed and justified. A typology of physical concepts is the real key to the opposition between philosophy of nature and positive science.

Let us try to ascertain rigorously the meaning of a word found both in philosophical and in positive contexts. The example chosen may be very simple. To the question what does the word "man" mean? the answer will be "rational animal"; now, none of the elements of this definition presents a character of irreducible clarity. Take one of them, for instance, animal. What does this word mean. A correct definition would be: "a living body endowed with sense knowledge," and these are so many terms which badly need clarification. Take for instance the expression "living." I would say that a body is a living one when it moves itself, when it is the active origin of its own development. If we go one step further, we go beyond the limits of physical thought. In order to render the idea of life clearer, we would have to define it as self‑actuation. The concept of self‑actuation does not imply any reference to the proper principles of corruptible and observable things: it is a metaphysical concept. Its elements are identity and casuality. Identity is the first property of being. Causality can be analyzed into potency and act. Identity, potency, and act are so many concepts directly reducible to that of being, which is, in an absolute sense, the first and the most intelligible of all concepts. We have reached the ultimate term of the analysis, the notion which cannot be defined and which does not admit of any beyond.

This is the kind of analysis that the word "man" suggests when it is used in certain contents. Everybody would agree that a discourse which demands such an analysis is a philosophical one. But the same word "man" is often used in contexts which neither demand nor could stand such an analysis. I happen to find the word "man" in a treatise of zoology: explaining it in the way we did just now would seem perfectly ridiculous. An analysis whose term is the concept of being has obviously nothing to do with the behavior, the method, the spirit and the principles of that discipline we call zoology. Should a univocally‑minded philosopher try to enlighten a zoologist by giving him explanations about self-actuation as a particular form of relationship between potency and act, no doubt the zoologist would declare that all these things are perfectly nonsensical for him as a scientist.

The zoologist would be right and the philosopher would be univocally‑minded. Both philosopher and zoologist consider man, but they have a different way of defining objects and of answering the question "what does it mean?" For the zoologist, man is a mammal of the order of primates. How would he define such a term as mammal? A vertebrate characterized by the presence of special glands secreting a liquid called milk. How is milk defined? In terms of color, taste, average density, bio‑logical function, chemical components, etc.

Here the ultimate and undefinable element is some sense datum; it is the object of an intuition for which no logical construction can be substituted and upon which all the logical constructions of the science of nature finally rest. In some cases, the explanation of a positive definition quickly demands recourse to sense experience. This often happens in the least elaborated parts of science. The elaboration of scientific concepts generally postpones the time when the recourse to sense intuition appears indispensable. But sooner or later it always imposes itself unmistakably. It is the possibility of being ascertained through sense experience which gives the concept its positive meaning. For the positive scientist every concept which cannot be, either directly or indirectly, explained in terms of sensations, is meaningless.

The philosophy of nature can be defined as a physical consideration whose conceptual instruments call for an ascending analysis, positive science as a physical consideration whose conceptual instruments call for a descending analysis. The very opposition of the two analyses provides an invaluable rule for the determination of the point of view prevailing in our studies about nature. Let us think of the ambiguous literature which stands on the borderline between philosophy and positive science. Then a philosopher informed of positive science or a scientist interested in philosophy considers philosophical problems raised by the study of positive questions, the philosophical and the positive point of view appear successively in his expositions; generally the writer is not aware of the shift. The resulting confusion can easily be removed provided we carry out the analysis of a few key concepts. According as this analysis goes up or down, according as the concept demands to be explained in more and more characteristically ontological terms or in terms which refer more and more directly to definite experiences, we know whether we have to deal with a philosophical or a positive treatment.

This description of positive science as a consideration of the ens mobile seu sensibile, which puts the emphasis upon mobile seu sensibile and centers around the observable aspects of things, throws a novel light on the notion of the science of phenomena. Let us have a glance at the adventurous history of this notion.

At the dawn of Greek philosophy, a science of phenomena was deemed impossible both by Parmenides and by Cratylus. Science demands an unchangeable and necessary object; the phenomenal universe shows only a stream of changing appearances. The phenomenon, owing to its mutability, is thoroughly uncongenial to the spirit of scientific knowledge. This negation persists in Plato. The phenomenal world is merely an object of opinion. Science finds its object in a transcendent world of numbers and ideas.[2] With Aristotle the picture is quite different. Aristotle perceives immutable types immanent in the physical world: these are universal natures which reveal themselves through the regularities that are observed in the very order of phenomena. Accordingly, the phenomenon no longer has the character of an enemy of scientific thought. It is the phenomenon which, through its regularities, leads the scientific mind to its object: the universal types of things, their essences, their ways of being. The science so defined is a philosophy of nature, an ontology of the physical world. It does not reach its end until it is able to answer the question "What is the thing under consideration?" Neither Aristotle nor any of his Thomistic followers has ever defended the unwarranted idea of an intuitive perception of essences. Yet their scientific ideal is definitely attached to the disclosure, the understanding of the intelligible types immanent in the observable world. However essential the observation of phenomena maybe in such a science, this science is by no means a science of phenomena. It is exclusively, or rather claims to be—for Aristotle did in fact perform great achievements in empiriological disciplines—a science of the essences located beyond the phenomena.

It can be safely said that the science of phenomena did not receive an epistemological charter before Kant. The charter it was given by Kant is idealistic. Hardly conscious of its nature in the era preceding the Kantian Critique, the science of phenomena, from then on, was to be acknowledged as a distinct and fully legitimate epistemological species. But how is the old problem answered in the Critique of Kant? What sort of solution is given to the difficulty resulting from the sharp conflict between the requirements of the scientific spirit—necessity, universality, inter-subjectivity—and the most obvious characteristics of the phenomenal world, its endless diversity, its thorough unsteadiness? There can be no doubt about it: the principles which, according to Kant, organize nature, do not lie in nature, but in the mind. The scientific object, with its characteristics of orderliness, determination, and universality, results from the application of mental categories to the diversity of sense‑experience data.

Most men of science, ever since the Kantian reformation, have assented to the fundamentally idealistic view that the characteristics of the scientific object, its aptitude to fit in an intelligible system and, above all, to comply with the requirements of casual identification, are a proper effect of the synthetic activity of the mind. This stubborn adherence to an idealistic justification of positive science conflicts strikingly with the spontaneous realism of scientific thought. Men of science, willingly or not, receive their philosophical ideas from philosophers; they could not rid themselves of idealistic prejudices so long as philosophers were teaching idealism as the only doctrine that could account for the unquestionable ability of the mind to treat in an orderly and causal manner the universe of phenomena.

In his dealing with phenomena, Aristotle has no other purpose than that of utilizing their regularities in order to know essences. Maritain calls dianoetical intellection the act of the mind which penetrates an essence and perceives what the thing is. For instance, the philosophical definition of man as analyzed above expresses an intellection which, though inexhaustive and non‑intuitive, has succeeded in penetrating the whatness of human nature. We know that the theoretical intellect is not often so successful. In most cases we cannot disclose the essences of sensible things in their specificity, we cannot accomplish a dianoetical intellection of their whatness. All we can do is to distinguish them through a definition calling for a descending analysis. The intellection expressed by such a definition does not imply any penetration of the physical essence; it only implies a circumscription of it within a steadily connected set of observable regularities. Nobody can say what the essence of silver is; yet silver is a perfectly distinct chemical species. The undisclosed essence called silver is clearly and certainly distinguished from any other essences[3] by the system of observable regularities which taken together belong exclusively to it.

In this connection let us call attention to a difficulty often experienced by positive scientists when they try to give their definitions a logically satisfactory form. Since we include in the definition of silver the property of melting at 960.5° centigrade, the property of boiling at 2000°, etc., what does the subject, silver, refer to, if not to something which is specified precisely by the fact that it melts at 960.5°? The vice of circularity seems inevitable. The statement that silver melts at 960.5° resembles very much the statement that a black cat is black. Or, if we wish to avoid mentioning the predicate in the logical subject, we are confronted with a host of predicates hailing upon nothingness as a subject. In fact a subject is not lacking, but whereas the many predicates belong to the order of phenomena, the subject belongs to another order. Throughout the chapter of chemistry which constitutes the definition of silver, a certain ontological x designated by this name, silver, is present, though undisclosed, to the mind. The logically satisfactory definition of silver would be: x melts at 960.5°, boils at 2000°, etc.; we give the name of silver to the hidden essence which we circumscribe by this steadily connected set of observable regularities.

Whereas the being of things is successfully penetrated by the dianoetical intellection used in philosophy of nature, it is only circumscribed by the perinoetical intellection of empiriological science. The intelligible element which enables empiriological knowledge to transcend empiricism is not revealed to the mind, nor is it imposed by the mind upon the phenomena as a form upon a matter. It is grasped inside a system of phenomenal regularities, circumscribed by this observable system and never disengaged from it. Thus the science of which Aristotle had no clear notion— although he practiced it a great deal— the science which has for its object the phenomenal regularities themselves, is defined as possible on a realistic basis. The orderly character of the phenomena is guaranteed by the ontological x which is confusedly grasped together with them by the empiriological analysis. With Maritain, the science of phenomena was given for the first time a justification which owed nothing to the idealistic interpretation of the mind's activity.

It is clear that in this conception a positive science of nature can exist independently of any mathematical treatment of natural phenomena. The Kantian statement that "the amount of genuine science found in each department of natural knowledge cannot be greater than the amount of mathematics found in it" shockingly conflicts with the fact that most important developments whose scientific character can hardly be questioned seem to be by nature refractory to mathematical forms (in biology and psychology especially). Whenever the mind seizes an essence, a ratio entis, albeit in the imperfect way proper to the perinoetical intellection, a genuinely scientific treatment remains possible. Any universal and necessary form of being, even if it is understood in a very obscure manner, constitutes a matter to which the mind can apply the principles of scientific thought, that is, causal and explanatory schemes. With great care Maritain pointed out that causal ideas and principles, when applied in empiriological sciences, have to be reconsidered and reshaped. The concept of efficient cause, for instance, is originally an ontological concept, that is, a concept defined by reference to being; in this original condition it is not directly applicable outside the ontological order. When we go down to the empiriological level, the concept of being undergoes a trans‑formation. Here, being no longer appears as the lighted spot of the thing under consideration, but merely as an undisclosed principle of orderliness which guarantees the steadiness of the phenomenal regularities.

Causal concepts have to undergo a transmutation completely analogous to that undergone by the concept of being. This operation can make them hard to recognize, and this is how some extreme forms of positivism have been able to construct the ideal of a science exclusively concerned with laws and which would owe nothing to causal concepts. But it is well known that the spontaneous development of positive sciences has constantly given the lie to this ideal limit of positivism.

Considering again the contention that Thomism cannot account for modern epistemological developments, let us now remark that it refers especially to the mathematical aspect of modern science. Did not the Cartesian reformation consist in the substitution of a mathematical interpretation of the physical world for the Aristotelian interpretation of nature in terms of ontology?

The mathematical treatment of physical nature was not unknown to ancient and medieval Aristotelianism. Astronomy, optics, and acoustics, are referred to in the works of Aristotle and his medieval for towers as so many mixed sciences, whose form is mathematical and whose matter is physical. In this connection, it is necessary to correct current statements concerning the lack of explicit distinction between philosophy and positive science in ancient and medieval doctrines. Old Aristotelians failed to distinguish clearly two types of thought, corresponding to distinct degrees of abstraction within the first order, and the term physicus is taken by them as entirely synonymous with the term philosophus naturalis. In that sense it is true that up to the modern era philosophy embraced all sciences of nature. But this holds only so far as positive research follows purely physical ways. Ancient and medieval philosophers seem to be rather keenly aware of a discrepancy between the ways proper to the philosophia naturalis and those proper to physico‑mathematical sciences. Whereas it never occurs to them to set in opposition the physicus and the philosophus naturalis, they currently set in opposition the philosophus physicus and the astronomer, thus showing some realization of the non‑philosophical character of the mathematical interpretation of nature.

Maritain describes the epistemological crisis which broke out at the time of Galileo and Descartes and is still so far from being settled as a tragic misunderstanding.[4]  When the historic conflict between the Aristotelian physics and the new physics broke out, both sides were equality convinced that this was a conflict between two philosophies of nature. The physico‑mathematical science founded by Descartes was considered by its founder as a philosophy of nature and the only possible one. The decadent Aristotelians with whom Descartes was confronted did not even think that the Cartesian world‑picture was possibly a physico‑mathematics sophisticated into an ontology. Then it happened that the Cartesian mechanism achieved the obliteration of the old distinction between the philosopher of nature (physicus) and the mathematic at interpreter of nature (astrologus). When we reread the great work of Newton significantly entitled Principia Mathematica Philosophiae Naturalis we realize that the Newtonian science, once considered by positivists as the archetype of positive knowledge, was far from having rid itself of ontological ambitions.

Thanks to his felicitous description of a non-philosophical approach to the physical world within the first order of abstraction, Maritain found himself in a favorable position to investigate the principles of physico-mathematical knowledge and to account for the increasingly complete autonomy which marked its latest developments. In this undertaking, Maritain had at hand two effective instruments: one was the theory of perinoetical intellection and descending analysis; the other was the conception of the mathematical object as a preter‑real entity always affected by some conditio rationis and which often turns out to be a mere ens rationis with a foundation in the real.

It is comparatively easy to see how the law of the descending analysis which prevails in all fields of positive knowledge applies to the mathematical interpretation of nature. Whereas in the case of a non-mathematical positive science the law of descending analysis amounts to the necessity of resolving all concepts into observable data, this law, when applied to a science of physico-mathematical type, signifies the necessity of resolving all concepts into measurable data. In several domains, nothing in general makes sense for the positive scientist except what can be explained in terms of measurements. A great deal of confusion often results from the fact that the philosopher of nature and the physicist use the same terms without being aware of their referring to widely different objects. One and the same term refers to the being of things when used by the philosopher and, when used by the physicist, to the aptitude of things to be the matter of accurate measurements.

No wonder that such widely different points of view give birth to statements which in appearance conflict sharply. The conflict generally vanishes as soon as we understand that identical words convey typically different concepts and refer to distinct objects. A particularly clear example is supplied by the recent discussions about the determination of natural phenomena. Many philosophers and scientists attribute to the so-called indeterminism of modern physics revolutionary consequences with regard to our philosophical conception of the natural and even of the human world. Yet it should be remarked that the point of reference used by the physicist in his definition of determinism is quite distinct from the point of reference used by the philosopher in the definition of a concept which bears the same name. True to the law of ascending analysis which is that of philosophical thought, the philosopher considers that an event is determined when in some way or other it happens necessarily; necessity itself is defined as the property of that which cannot be otherwise than it is. The reference is ontological; the concept so defined makes absolutely no sense for the physicist. Being and the possibility of being otherwise are not things which fall under his measurements. Accordingly, in order to be of any use in physics the concept of determinism has to be reshaped so as to satisfy the following proportion: the determinism of the physicist is to the determinism of the philosopher as the measurable is to being. Thus we are led to realize that whereas the philosopher understands by determined event an event which follows from its causes in such a way that it cannot fail to happen, the physicist understands by determined event an event whose coordinates at the time t can be accurately calculated on the basis of an initial system of spatio‑temporal data. The determinism of the physicist is an empiriometrical determinism.

Because of the intervention of the mathematical ens rationis the gap is wider between philosophy of nature and physico-mathematics than between philosophy of nature and other parts of positive science. In so far as physics is a formally mathematical science, in so far as it obeys the law which is that of its form, it participates in the indifference of mathematics to the reality of its object. This consideration accounts for the particular form taken in our times by the old conflict between science and common sense.

The congeries of current notions that we call common sense is far from being homogeneous. Maritain distinguishes in it a system of images and a rudimentary ontology. The imagery of common sense expresses mostly the laziness of uncultured intellects and their willingness to content themselves with cheap representations. No wonder that this imagery has always conflicted with science and generally with every form of rational thinking. But inasmuch as physics incorporates entia rationis and follows the mathematical tendency to treat indifferently entia rationis and entia realia, even the sound part of common sense, its ontology, may enter into conflict with the most sound scientific speculations. The concept of relative simultaneity, for instance, appears very shocking to common sense; common sense unhesitatingly believes that the question whether two events happen at the same time must be answered by yes or no. Ontologically considered, simultaneity is absolute. Yet the concept of relative simultaneity makes sense if referred to definite possibilities of accurate measurements; this reference is thoroughly unfamiliar to common sense. Relative simultaneity is a physico‑mathematical ens rationis founded in the real and inescapably imposed upon the mind of the physicist by the very nature of his scientific point of view.

From this it does not follow that the constructions of the physicist should be considered as mere "hypotheses" or conventions incapable of apprehending the real in any way. Maritain would not agree with the superficial statement that the philosopher has never to worry about agreements or disagreements with the physicist, on the ground that philosophy and physics are two separate domains of thought. His epistemological pluralism is by no means absolute. Let us give an idea of the distinctions which should be made and of the issue which should be surveyed in order to appreciate the bearing of physical theories with regard to the knowledge of the real.

1. The principles previously developed make it clear that a concept may be a genuine expression of the real without pertaining to the ontological type. A description of a non-ontological character is not thereby deprived of real bearing. Real, being, knowledge are so many analogical terms. An ontological description is more real than a non-ontological one, yet a non-ontological description may well be a description of the real.

2. Even within the first order of abstraction the mind often uses fictitious constructions in its approach to the real. Yet so long as were main in the first order, the realistic spirit of science is not held in check. Except for possible failures, fictions never play more than a transitional role; they are used as mere means in view of achieving a representation of the real which cannot be brought about in a more direct fashion.

3. As soon as positive science assumes a mathematical form, something entirely novel takes place. The very nature of mathematical abstraction renders mathematical thought indifferent to the reality of its object. Consequently physico-mathematical science, in so far as it yields to the attraction of its mathematical form, tends to make no difference between ens reale and ens rationis.

4. Should this tendency prevail without check, it could be said truly that physical theories do not trace phenomena to their real causes and do not tell anything about the real world. Such is the conception of physics upheld by Pierre Duhem. For Maritain this interpretation, though not without basis, amounts to an oversimplification. In fact, the attraction exercised on physics by its mathematical form is not unchecked. If the form is mathematical, the matter remains physical, and accordingly there is in the very structure of the science a counteracting tendency to adhere to the real and to look for explanations by real causes. Actual science is probably a compromise between these two opposite and complementary tendencies.

However incomplete it may be, this exposition sufficiently shows that for Maritain the problem of the relationship between science and philosophy does not admit of any easy solution. Maritain is quite aware of the great improvements in knowledge which can be expected from the cooperation of the philosopher and the scientist; but he does not seem to believe that such a cooperation can ever work smoothly and without frictions. The ample system of our knowledge of nature—philosophical, empiriological, empiriometrical—is apparently destined to present ever‑lastingly a spectacle of restlessness, of precarious equilibrium, with sharp conflicts breaking out in times of crisis. Such a lack of harmony would be sufficiently accounted for by the psychology of the scientist and that of the philosopher. It is difficult, not to say impossible, for each of them not to be biased by his own habitus to the point of being unable to understand his partner. But even if a perfect philosopher were also a perfect physicist, or vice versa, there still would be within the mind, provided with such habitus, ground for conflicts between the two visions of the world. Maritain says that there is some melancholy in the realization that no complete continuity can be established among our various approaches to the natural world. It is not the least merit of his extensive and profound exploration of the most diverse fields of rational activity to have removed the optimistic illusion of a perfect harmony among the functions of the mind.

Compared with the teaching which prevailed in Thomistic textbooks thirty years ago, Maritain's philosophy of science appears as a tremendous novelty. Yet whoever is familiar with the physical and epistemological writings of St. Thomas will admit that no Thomist has ever written a more authentically Thomistic book than The Degrees of Knowledge.



[1] The main writings of Maritain concerning the philosophy of sciences are: Refections sur intelligence (Paris, Desclée de Brouwer 1924); Distingeur pour unir, ou Les Degrées du savoir, (Paris, Desclée de Brouwer, 1932), English trans. The Degrees of Knowledge, (New York: Charles Scribner's Sons, 1959) trans. Gerald B. Phelan); La Philosophie de la nature, (Paris: Pieere Téqui, 1935), English trans. Philosophy of Nature Amelda C. Byrne (New York, Philosophical Library, l95l); Science et sagess (Paris: Labergerie, 1935); Science and Wisdom (New York: Charles Schribner's Sons, 1940), trans. Bernard Wall; Scholasticism and Politics (New York: Macmillan, 1940), translation ed. Mortimer J. Adler, ch. 2; "Philosophy and the Unity of the Sciences," in Proceedings of the American Catholic Philosophical Association, XXVII (1953), pp. 34-56. [This footnote originally written in 1943, has been updated. ed.].

[2] It goes without saying that in this sketch we content ourself with pointing out major features of the systems under consideration.

[3] I abstract from the question whether an empiriological species like silver coincides with an ontological species, or is merely a sub‑determination of a broader ontological species.

[4] See "The Conflict of Methods at the End of the Middle Ages," The Thomist, III (1941), pp. 527‑538.