Theory and History of Ontology ( Raul Corazzon | e-mail:

Semiotics and Ontology: The Rediscovery of John Poinsot (John of St. Thomas)

Contents of this Section

This part of the section Theory of Ontology includes the following pages:

The Rediscovery of John Poinsot (John of St. Thomas) (Current page)

Selected bibliography on John Poinsot

John Deely. An Annotated bibliography:

1965 - 1998

1999 - 2010


"The seventeenth-century Portuguese Dominican, John of St Thomas or John Poinsot, was a major figure in late scholastic philosophy and theology. Educated at Coimbra and Louvain, he taught both disciplines in Spain: at Madrid, Plasencia and Alcalà. Aspiring to be a faithful disciple of Thomas Aquinas, he published a three-volume Cursus philosophicus thomisticus (Thomistic Philosophical Course) and before he died began the publication of a Cursus theologicus (Theological Course). His philosophical writing was explicitly on logic and natural philosophy. However, in both his philosophical and theological works, he treated many metaphysical, epistemological and ethical issues. His logic is divided into two parts, formal and material. Of particular interest is his semiotic doctrine which appears in the second part. In natural philosophy, he explained Aristotle with a Thomistic slant. While following Aquinas in theology, John at times developed his master's doctrine along new lines."

From: John P. Doyle, "John of St. Thomas (1589-1644)", - in: Edward Craig (ed.), Routledge Encyclopedia of Philosophy, vol. V p. 117-120, New York: Routledge 1998.

"Thus the story even of the sign begins with the discovery of nature as a reality prior to and in various ways escaping human purposes. The story of the sign, in short, is of a piece with the story of philosophy itself, and begins, all unknowingly, where philosophy itself begins, though not as philosophy. To proceed to tell the story of the sign in other ways is of course not impossible; but each such alternative approach leaves out too many of the pieces needed even for the effort of re-telling the story more succinctly when we turn around to explain what we have discovered - at least if we want to tell the tale in the most convincing and complete manner possible.

Our purpose in these pages, then, is to make the discovery which, we will argue, introduces postmodernity (the end of the story for now) clear and credible, and for this nothing less than a general history of philosophy will do. Even if we do not have to explore every theme of that history, we must yet explain all those themes that pertain to the presupposition of the sign's being and activity, in order to arrive at that being and activity with sufficient intellectual tools to make full sense of it as a theme in its own right. And those themes turn out to be nothing less or other than the very themes of ontology and epistemology forged presemiotically, as we might say, in that laboratory for discovering the consequences of ideas that we call the history of philosophy'. If the discovery of the sign began, as a matter of fact, unconsciously with the discovery of nature, then the beginning of semiotics was first the beginning of philosophy, for only as philosophy are the foundations of semiotics possible - even if semiotics is what philosophy must eventually become, as we shall see. Nothing begins where it ends; the best stories are told not from the middle; and, while the end of a tale may do much to illumine its beginnings, the end is hardly a substitute for the beginning."

From: John Deely, Four Ages of Understanding. The First Postmodern Survey of Philosophy from Ancient Times to the Turn of the Twenty-First Century, Toronto: University of Toronto Press 2001, pp. 19-20.

"On the showing of his volumes' titles, Poinsot treats of Logic and Natural Philosophy. As a matter of public avowal he treats neither of Metaphysics nor of Ethics, whence to one inspecting the work superficially will it readily appear that Poinsot has said nothing or next to nothing on these matters. But to anyone who not only looks at the index of questions and articles, but who also reads the text attentively in its entirety, will find that practically everything expounded by modern authors under the title of Ontology can be found in Poinsot under his treatment of Material Logic and under his treatment of causes and the ground of motion in the Natural Philosophy. Likewise for the fundamentals of Criteriology, which can be found treated in the Second Part of the Logic in the questions on foreknowledge and premises, demonstration and scientific knowledge. The fact that our author does not provide a specific dissertation on Metaphysics and especially on Ethics within the compass of his Cursus Philosophicus, while unfortunate from our point of view, should not lead anyone to think that Poinsot has written little or nothing on these for matters in other places. Matters pertaining to natural theology and to ethics were left for thematic treatment in the Cursus Theologicus, according to the custom of that age, and, specifically, the matters of natural theology to the Commentary on the First Part [Poinsot, Tomus Primus Cursus Theologici1637, Tomus Secundus 1643], those of Ethics to the Commentary on the Second Part [Poinsot Tomus Quartus and Quintus 1645, Tomus Sextus 1649] of the Summa Theologiae of St. Thomas, where all these matters are found treated at great length." (p. XII)

From: Beato Reiser, Editoris Praefatio to: Ioannes a Sancto Thoma (Poinsot) Ars logica (1631-1632) nova editio a Raiser, Turin: Marietti 1930.

The name: João Poinsot - Joannes de S. Thoma - Juan de Sto Tomás - Jean de St.Thomas - Giovanni di S. Tommaso - John of St. Thomas

"It is not often that a special discussion has to be devoted to the name of the author of a given work, though indeed such a problem is far from unheard-of. There are a number of considerations that make such a discussion useful in the present case. Accordingly, I will proceed to identify the author of our text in two steps: First, by explaining why I have settled on 'John Poinsot' as the most appropriate for our purpose of the several variant names he might be and has been called by; Second, by recounting the events of his life in the context of European history of the time.


The principal posthumous editors of Poinsot's works - Reiser in the case of the Cursus Philosophicus, the Solesmes editors in the case of the Cursus Theologicus - use for their author's name the Latin form "Joannes a Sancto Thoma" ("John of Saint Thomas"). It was this name in this form that Poinsot himself attached to the first three volumes he himself edited of his Cursus Theologicus.

Nonetheless, the following three posthumous volumes of the Cursus Theologicus revert to the variant, "Joannes de Sancto Thoma," which is also the form used on the early editions of the volumes of the Cursus Philosophicus one time, in the 1635 Douai edition of the Artis Logicae Prima Pars, with the spelling "Johannes..."In personal correspondence, our author often wrote and signed in the vernacular of Spain, "Juan de S. Thoma" (or "Thomas," "Toma," "Tomâs").

The Solesmes editors seem to think that use of the Latin "de" form arose in this case from assimilation to the Spanish version of the Latin "a Sancto Thoma," to wit, "de Santo Thoma" (and "de Sancto Thoma" is not incorrect Latin in any case), but that it was "a Sancto Thoma" that was the form Poinsot actually received in religious life.

The surname "Poinsot" certainly belonged to our author by birth, but its etymological connotations create yet other problems in the present case, since to modern ears it is unmistakably French in flavor, though our author's father came from Austria while his mother (Maria Garcez) was Portuguese, and he himself was educated in Portugal and Belgium, after which he entered for the rest of his life the heartland of Spain, where he studied, taught, and labored, ending his days in the Council of the King. Living at the time just prior to the emergence of the nation states as we think of them today, Poinsot belongs to no "nationality" in the usual sense.

Portuguese by maternal blood, Viennese and French (Burgundian) by paternal blood, Portuguese, Belgian, and Spanish by education, it is very difficult to say how such a man identified himself in the civil order. How would he think of himself? Certainly, no modern category would be the likely answer to that question.


On all versions, John is the English form of our author's first name. That his family surname was Poinsot is equally certain. Hence, for our English edition of his semiotic,. the first such in any language, we thus nominally identify our author." (pp. 421-424, notes omitted)

John Deely, "Editorial Afterword" to the Tractatus de Signis. The Semiotic of John Poinsot, Berkeley: University of California Press 1985.

Tractatus de Signis

"The semiotic of John Poinsot here presented autonomously for the first time was disengaged from a larger work entitled the Ars Logica, itself but the first two parts of a five-part Cursus Philosophicus. Since this work has a considerable historical interest in its own right, and in order to minimize the violence of editing the tractatus de signis into a whole independent of that original context, we have settled on the following manner of presentation.

Putting ourselves in the position of a reader coming to the Ars Logica for the first time and interested only in Poinsot's discussion of signs, we asked ourselves: What sections of the work would this hypothetical reader have to look at in order to appreciate that discussion both in its own terms and in terms of the whole of which it originally formed a part? To what extent are these separable philosophically? The pages that follow make up our solution to this problem. We have left Poinsot's text stand virtually entirely according to the order he proposed for it within the Ars Logica as a whole. To make this order clear, we have included title pages, and all general statements Poinsot set down concerning the whole (and therefore the Treatise as part), inserting where appropriate and to bridge necessary jumps a series of brief comments designated "semiotic markers," designed to show the reader how the rationale of all editing is derived from the original author's own intentions; and second, we have included all and only those sections of the whole which have a direct bearing on understanding the doctrine proposed in the Treatise on Signs proper, as the semiotic markers make clear.

In other words, we have tried to provide the reader with a guided tour of the Ars Logica that leads directly to an understanding of the doctrine of signs contained in that work, but does so by enabling him or her to appreciate the historical origin of the account in the context of its author's own understanding of previous logical and philosophical traditions. We have chosen this format as the one best suited, so far as we could judge, to exhibit the unique mediating status Poinsot's Treatise occupies "archeologically," as it were, in the Western tradition between the ontological concerns of ancient, medieval, and renaissance philosophy, and the epistemological concerns of modern and contemporary thought.

At the end of the work, the reader will find a lengthy "Editorial Afterword" explaining the entire work and giving its background and prospectus, much the sort of materials commonly given in an Introduction to a translated work. The device of the semiotic markers made it possible in this case to bypass the need for lengthy introductory materials enabling the reader to grasp the editorial structure of the whole, yet without of course obviating the need for detailed discussions somewhere of the principles of the English text, and of the historical situation of the author and his work. Thus we have been able to enter simply and directly into the doctrinal content of the main text, without cluttering its entrance with more than a very few lines of contemporary origin.

The reader will also find at the end of the work a complete series of indices to this entire edition, both to its main text (which indices are explained at length in the "Afterword" just mentioned) and to its accompanying editorial materials, followed by a comprehensive list of Bibliographical references. Bibliographical references not complete in the markers or in the notes on the text will be found there. All indexical references to the Treatise itself with its attendant parts (i.e., to the bi-lingual portions of this edition) are by page and line numbers, thus providing the reader with the exact place of each reference in this English edition of Poinsot's text and, at the same time, the almost exact place in the parallel column of the Latin original. Similarly, all cross references to other parts of Poinsot's Cursus Philosophicus, as in the running heads of the present edition, are according to the pages, columns (a, b), and lines of the Reiser edition, as set out in the "Abbreviations" immediately preceding this preface." (pp. 1-2)

John Deely, "To the Reader of this Edition", Tractatus de Signis. The Semiotic of John Poinsot, Berkeley: University of California Press 1985.

Outlines of Formal Logic

"The Ars Logica is a long work of 839 double-columned pages, some 280,000 words. Its two main divisions are: Formal Logic and Material Logic. As John of St. Thomas puts it: "In the first part we deal with everything that belongs to the form of the art of Logic and to prior resolution. These are the things Aristotle dealt with in De Interpretatione and Analytica Priora, and are customarily taught beginning students in Outlines. But in the second part we shall deal with everything that belongs to logical matter, or to posterior resolution, especially as it is in demonstration, towards which Logic is principally ordered."The First Part contains a short text of formal Logic suited for beginners, followed by an explanation for advanced students (in 8 "Quaestiones Disputandae ad Illustrandum Difficultates Aliquas Huius Textus," subdivided into 29 articles) of the more difficult points of the short text. Only the short text for beginners is translated in the present volume.

The Second Part is "longer and more diffuse because the matter of any art normally has more things demanding consideration than the form does." The proper matter of the art of Logic will be propositions in which a demonstration can take place. If strict demonstration requires reduction to principles known per se, then the propositions strictly demonstrable must be those that are necessary and per se connected. Now, we know that contingent predicates give contingent propositions. For necessary propositions we need essential or proper predicates. Here then we have a means for discovering necessary matter: unfold the ordered lines of the predicaments, in which all things are reduced to their top genera, and where for each predicament is given the higher and lower predicates between which an essential connection is discovered. However, since predicaments cannot be known without the predicables, which are the modes of predicating essentially or accidentally, these too must be matter for the art of Logic. Thus the matter of Logic contains these three: 1) predicables, the modes of predication; 2) the ten predicaments, the classes and top genera to which all natural things and their essential predicates are reduced; 3) the forming of per se propositions and strict demonstrations. These, then, are the three divisions of Material Logic. For the first, John of St. Thomas bases his teaching on the text of Porphyry. For the last two, on the texts of Aristotle. And as a sort of introduction to the whole of Material Logic he considers (in 5 questions and 24 articles) the nature of the science of Logic itself. The most fundamental parts of his Material Logic have been translated by Yves R. Simon, John J. Glanville, and G. Donald Hollenhorst.

According to John of St. Thomas, and to Aristotle and St. Thomas before him, Logic deals with the operations of reason. Its "function is to direct the reason lest it err in the manner of inferring and knowing." The natural divisions of Logic then follow the different kinds of mental operations. Thus Formal Logic is divided into three books: 1) what pertains to the simple apprehension (first operation of the mind); 2) what pertains to judgment (second operation) ; 3) what pertains to reasoning and inference (third operation). Material Logic too, though indirectly of course, is divided according to the mental operations. Its direct object is the matter, taken generally, that the mind deals with, i.e. necessary predicates and their connecting lines. Still, the manner of predicating, the reduction of all essential predicates to the ten predicaments, and the forming of per se propositions and strict demonstrations are mental operations even when they depend on the matter known." (p. 5-6, Notes omitted)

Francis C. Wade, "Introduction" to John of St. Thomas, Outlines of Formal Logic, Milwaukee: Marquette University Press 1955.

The Material Logic of John of St. Thomas: Basic Treatises

"We do not need to elaborate on the reasons why the integral translation of a work which fills 839 two-column pages in the latest edition was held impossible. Since a choice had to be made, we turned to the field of material logic, where the shortage of great books is particularly felt. (...) But no more than about three fifths of John of St. Thomas' writings in material logic could be included within reasonable space limits. Our choice was governed by both doctrinal and pedagogical concerns. We made it a rule never to abridge an exposition having the character of a whole. Our shortest units are long articles. In several cases, our unit is a whole "question." On the subject of demonstration, it is the whole set of "questions" corresponding to the Posterior Analytics.

Whoever is aware of the situation of logical studies in our time knows that the most vexing of our problems is the problem of logic itself. Accordingly, much space is given to the issues concerning the object and nature of logic (I). The problem of the universal (II) is obviously of central significance for all logic and for the philosophy of knowledge. The "antepredicamental" discussions (III), consisting principally of an inquiry into analogy, constitute a masterly contribution to the theory of meaning. The doctrine of analogy presented here is the subject of further developments in the articles on the division of being into categories (IV). The long study of the first four categories (IV) is a store of elaborate information on concepts basic in all parts of philosophy and in the interpretation of the sciences. From a certain standpoint, the pages on quantity and on relation can be considered supplementary to the introductory pages on the object of logic. Taken together, these three sections present much material and many precise instruments for the improvement of our ideas on the relations between the logical and the mathematical sciences. Section V is concerned with four timely issues: signification, the relation of knowledge to actual existence, reflection, and formalization. Lastly (VI) we present without any omission John of St. Thomas' treatment of demonstration and science.

(...) Much of the doctrine contained in John of St. Thomas' formal logic is available in the Formal Logic of Jacques Maritain. The Short Treatises which, from a pedagogical standpoint, constitute the core of John of St. Thomas' teaching in formal logic, have been translated by Francis C. Wade under the title of Outlines of Logic (Milwaukee: Marquette University Press, 1955)." (pp. XX-XXI)

Yves R. Simon, "Foreword" to The Material Logic of John of St. Thomas: Basic Treatises, Chicago: University of Chicago Press 1955.

Introduction to the Summa theologiae of Thomas Aquinas

"One might expect a Thomist of the strict observance to engage in the kind of close commentary on the text that characterized Thomas's own commentaries on Aristotle, or Cajetan's on the Summa, but in both his philosophical and his theological work, John writes in relative independence of the text that prompts the discussion. He will summarize rapidly the relevant work of Aristotle, and then go on to a discussion guided as much by later controversy as by the text itself. So, too, there is in the theological writings a kind of tour de monde survey of what others have said on the question before launching into his own solution. But the vast theological effort was prefaced by three sizeable Essays: an analysis of the Sentences of Peter Lombard, a discussion of the authority the thought of St. Thomas enjoys in the Church, and the analysis of the Summa theologiae translated here. The full title is: Isagoge ad D. Thomae theologiae. Explicatio connexionis et ordinis totius Summae Theologiae D. Thomae, per omnes ejus materias.

John's introduction is just that - it is not a commentary or analysis of the text of the Summa theologiae, but a bearing of its infrastructure, displaying the ordering principles that brought together the vast treasury of Christian theology in as economical and perspicuous a manner as possible. In many ways, John's task was simple: all he had to do was pick up on the quite overt remarks of St. Thomas as to why a topic or treatise comes before or after others, what the inner ordering of a treatise was, what the ordering of the articles within a question was, and, not to put too fine a point on it, why the objections in a given article come in the order they do. The Summa theologiae was written for theological, though not philosophical, beginners, and it aims to give a swift, accurate, and adequate sense of the theological terrain. From that point of view, John can be said to have provided an outline of an outline. This is not to disparage what he has done. There are enormous advantages to being acquainted with the skeleton of the Summa before examining the flesh that covers it. There is no need to overstate John's achievement to see it as something for which the neophyte can be grateful and which, even for one who thinks himself an adept, not only reinforces the old sense of the storied order of the Summa but, in its hurried and pedestrian prose, contains more than one precious nugget absent from more ambitious commentaries." (pp. IX-X)

Ralph McInerny, "Preface" to Introduction to the Summa Theologiae of Thomas Aquinas: The Isagoge of John of St. Thomas, South Bend: St. Augustine Press 2004.

Poinsot's contribution to logic and semiotic

"Poinsot, so far as present knowledge goes, holds the privileged position in semiotic historiography of being the earliest systematizer of the 'doctrine of 'signs. Not until the work of Peirce in our own day do we again encounter a 'semiotic of comparable energy and scope. In 1632, Poinsot published, as part of his series of courses in philosophy at the University of Alcalâ, Spain, a highly original, systematically conceived Treatise on Signs (Tractatus de Signis) (1930), which fits exactly 'Locke's definition of semiotic proposed some 58 years later, at the close of his Essay Concerning Human Understanding (details in Deely, Introducing Semiotic. Its History and Doctrine, Bloomington: Indiana University Press 1982), and taken up again by Peirce.

From this point of view, Poinsot's work provides us with the first of several "missing links" in the history of logic and 'philosophy after 'Ockham (e. 1350), enabling us to trace backwards through the Iberian schools of Coimbra (notably in the work of Petrus Fonseca [1564] and the team of workers he organized, the so-called "Conimbricenses"), Salamanca (Suárez, Soto, and others), and Alcalâ, a heretofore largely untold story of developments that are exceptional in import for semiotics (Deely 1982).

Doctrinally, Poinsot's work achieves a new, entirely experiential point of departure for the enterprise of philosophy, and reconciles in so doing the seemingly opposed orders of nature and 'culture. Poinsot begins his Treatise on Signs by drawing attention to a central feature of 'semiosis that must, in his opinion, be a first concern of semioticians to safeguard and give adequate account of, namely, the fact that, in our experience, signs bring together natural and social phenomena. The sign, he points out (Book 1, Question I: 646b26-45), is something neither preclusively natural nor preclusively social, but both inclusively, for while all signs as such acquire their signification and actually exist only within some living being's experience, nonetheless, within that very experience, the connection between signs and what they signify sometimes seemsto have roots outside our experience of their connection (the case of "natural" signs), and other times seems to have no reality other than the one derived from the experience itself of social interaction (the case of customary and stipulated signs). Thus the first task of the semiotician, in Poinsot's judgment, is to secure a standpoint superior to the division of being into what exists independently of our 'cognition (ens reale 'mind-independent being') and what exists dependently upon cognition (ens rationis mind-dependent being'). For Poinsot, semiotic must take its stand, in the felicitous description by Sebeok, squarely "at the intersection of nature and culture." This simple description of semiotic's initial task already amounts to a revolution within the perspective of natural philosophy or "physics" traditional in Poinsot's day. For the sole concern of that tradition was to uncover and explicate the structure of ens reale, which they thought to have achieved, after "Aristotle, with the division of mind independent being into substances, or natural units of independent existence, with their accidents, or various properties and characteristics. Thus, the division of being into the Aristotelian categories of substance and the various types of accident was generally thought to be the permanent achievement of ontology in the Latin age.

Poinsot's approach to semiotic entirely undercuts this categorial scheme, going beneath it and beginning with an analysis of experience prior to the possibility of the working out of any such scheme. He establishes a fundamental ontology in just that sense which Heidegger calls for in our own time, namely, an "ontology" that accounts for the categorial interconnections and lays bare the ground of the prior possibility of truth as a "correspondence" between thought and being. Poinsot finds this fundamental ontology in our experience of the ways in which things appear to be relative. Poinsot observed (following in this Aquinas [Quaestione disputate de anima c. 1266: q. 28] and Cajetan [Commentaria in Summa theologicam, 1507] before him) that, as a mode of reality, relation is unique in that its essence (esse ad aliud 'being between') is separate from its cause or ground of existence (esse in alio 'the character or feature upon which a relation is founded'), which is not the case for any other mode of reality. Poinsot sees in this the ultimate reason for the possibility of semiosis: relation in what is proper to it, namely, suprasubjectivity or intersubjectivity (esse ad), is indifferent to realization now in nature, now in thought, now in both. Relation in this sense, precisely as indifferent to the opposition of what depends upon and what is independent of cognition, Poinsot calls relatio secundum esse 'relation according to the way it has being' or 'ontological relation' (see Deely 1982).

By contrast, things that are related exist subjectively as something in their own right, not just between other things sustaining them in a derivative way. And yet, if we seek to explain why they are as they are or how they might be altered from their present state, we find it necessary to refer to what the individuals in question themselves are not. Thus, even the individual entities and "natural units" of experience existing in their own right - even substances in Aristotle's scheme, the most absolute of the subjective entities - are seen to be relative when it comes to the question of how they come to be or of how they are to be accounted for. Relativity in this sense, precisely as infecting the whole scheme of categories of cognition-independent existents, Poinsot termed relatio secundum dici 'relation according to the way being must be expressed in discourse', or (synonymously) relatio transcendentalis 'transcendental relation'.

With this division of being, then, into transcendental and ontological relation, Poinsot has two simple "categories" that are exhaustive and exclusive, but whose terms are entirely matters of direct experience (unlike Aristotle's division of being into substance and accident, which was also exhaustive and exclusive, but directly experienced only on the side of certain accidents: comprehensive discussion in Powell [Freely Chosen Reality] 1982), and whose relevance to the doctrine of signs is immediate. For all authors agree, and indeed experience makes quite unmistakable, that every sign as such is a relative being (something making known another than itself), and since, by the prior terms of the analysis of relative being, we know that there are only two irreducible types of relativity, it remains only to apply that analysis to our experience of semiosis in order to determine in what precisely a sign consists (the formalis ratio signi, as Poinsot puts it), that is to say, what is it that constitues a sign in its proper being? The answer to this question is ontological relation, an answer which enables Poinsot to resolve a number of aporia that have plagued accounts of signifying from ancient times down to the present, and which turn out to be decisive for °epistemology and philosophical thought generally."

From: John Deely, "Poinsot, John", in: General Editor, Thomas A. Sebeok; Editorial Board, Paul Bouissac [et al.] Encyclopedic Dictionary of Semiotics, Berlin / New York: Mouton de Gruyter 1986.

"John of St Thomas' logic is divided into two parts. In the first part, his concern is with the formal theory of correct thinking. This part, which includes such medieval items as supposition, exponibles and consequences, corresponds especially to the Summulae Logicales of Peter of Spain and the Prior Analytics of Aristotle. In the larger second part, which corresponds to the Isagoge of Porphyry, plus the Categories and the Posterior Analytics of Aristotle, he deals with material logic, which is a general theory of scientific demonstrations and the necessary connections they involve depending upon their content. Organized according to the three operations of the intellect (simple apprehension, judgment and reasoning) the first part treats of terms, propositions, consequences and syllogisms, along the way attending to definitions, divisions and their various facets. In the second part, John reflects upon the nature of logic itself, which he thinks is at once an art and a science. As science, he says, 'logic is essentially and absolutely in virtue of its own principles speculative, but it takes on the manner of a practical science in so far as it offers rules and direction for speculation itself' (Ars Logica, II q.1 a.4). The object of logic is beings of reason, such as species, genus, subject, predicate, antecedent, consequent and so on, formed by the mind's reflections upon its own operations. Such beings of reason, which have some foundation in reality outside the mind, fall under a wider notion that includes beings of reason like chimeras. These last lack such a foundation because they are impossible (that is, self-contradictory) objects. Contrasted with both sorts of beings of reason are real beings which are divided into the various Aristotelian categories.

The categories are the central concern of the second part of John's logic. He rejects Duns Scotus' teaching that ens (being) is said univocally of the categories.. Rather, as Cajetan thought, 'being' as said of the categories is 'formally analogous with an analogy of proper proportionality' (Ars Logica, II q.14 a.3). Passing through each category in succession he concurs with Cajetan's interpretation of Aquinas (Summa theologiae Ia. 28.1) to the effect that relation is unique because it can be found in the order either of real being or being of reason. Only relation, since it is not just 'in' something but also 'towards' something, can transcend categorial status and be conceived apart from real existence either in itself (that is, the mode of existence proper to a substance) or in something else (the mode proper to an accident). This thought was to be central to John's doctrine of signs.

The doctrine of signs itself, which in part at least reflects the influence of John's Jesuit teachers at Coimbra, forms a treatise which runs over questions 21-3 in the second part of his logic. Essentially relational, signs are divided first into formal and instrumental, and second into natural, conventional and customary. All signs make something else known: formal signs (for example, a concept or an impressed species) do so without themselves first being known; instrumental signs (such as smoke or a spoken word) are themselves first known and then lead to the knowledge of something else. Natural signs (smoke) differ from conventional signs (words) inasmuch as the former simply arise from causal connections in the natural order while the latter result from human choice. Customary signs also result from choice but can be natural when a custom leads us naturally to its cause. Signs involve two non-reciprocal relations: between the sign and the significate (as in the relation of measured to measure) and between the sign and the cognitive power of a knower (as in the relation of measure to measured). Considered just as such, these relations are not in the line of physical causality but rather in that of intentionality in which the sign substitutes for the significate. Within this line of intentionality the ability of relation to transcend real being and being of reason becomes the basis of a unified semiotic doctrine respecting all signs of whatever sort they are."

From: John P. Doyle, "John of st. Thomas (1589-1644)", in: Edward Craig (ed.), Routledge Encyclopedia of Philosophy, New York: Routledge 1998.