De Praedicabilibus, Bk. I, Tr. I, Ch. 1
To those intending first about logic, it-must-be-considered what kind of science logic is, and whether it is some part of philosophy, and for what necessary, and of what usefulness; then moreover about what it is, and what the division of it is: so that, with all parts of it having-been-treated, it-may-be-known when it is perfectly or imperfectly handed-down or described.
Concerning all these things indeed, different things to say the Ancients seem. For certain of the Ancients already asserted logic to be science, saying logic not to be able to be science that which is the method of every science or doctrine. The method moreover of every doctrine is logic: because by some kind of persuasion uses everyone who teaches or tries to establish something; every persuasion moreover through speech is logic, whether by syllogism, or by enthymeme, or by induction, or by example uses the one who teaches or persuades.
The method therefore of every doctrine is logic. And thus the method of every doctrine is logical science. There is therefore no special doctrine which may be called logic. Because of which also Aristotle in the second of his First Philosophy, and similarly Averroes, say the method of every science to be the very science which is and is called logic, and that science and the method of science cannot at the same time be learned, but the method must first be learned, and then through the method already perfectly grasped, the intended science be learned.
But they did not consider sufficiently that, although sciences are many, and each has its own special method, which differs from the method of another, just as each science differs from another: there is nevertheless one common method of science through a certain common [thing] which is in every science. And this is what by investigation of reason from the known one comes to the knowledge of the unknown: this indeed happens in every science in whatever way it is called, whether it be demonstrative or not demonstrative. And for the sake of that common [thing], there is in every science one common method of all science.
And this method is through the act of reason, which is reasoning or argumentation, proceeding from the knowledge of the known into the science of that which was unknown, according as Isaac, in the book On Definitions, defining reason, says that reason is the intellectual power of the soul, making to run the cause into the caused. Calling “cause” generally and broadly, everything which according to the intellect simply, or with respect to us, precedes as known, through whose knowledge, by the leading of reason, one comes to the knowledge of the unknown.
This method, however, although it be common through that which is placed in each science, nevertheless considered according to itself and not mixed with the sciences, is something by itself distinct from all others. And in this way considered, this method can be the subject of a science, and a special science about it exists: in which science, however, the same method must be observed, because a science of such a method cannot be taught except by a logical method.
As Avicenna indeed says, this method is instilled in all men (through this [fact] that they are intellectual in some way by nature). But imperfect is that which is in nature: it is perfected, however, through applied art. For that which is in nature is a seed and imperfect, and as it were existing in potentiality.
From this, indeed, that man is intellectual and laid out for understanding—in which are spread intellectual forms in the act of the light of understanding—and through the intellect he is compositive of one form with another by composition or division, man becomes full of wonder at those things which he comprehends by receiving through sense and intellect, or by intellect alone.
By this, however, that he is full of wonder, he is drawn toward inquiry, and through inquiry he compares one thing to another. Through the comparison of one with another, from what is known one is led to the knowledge of the unknown.
And thus this logical method begins indeed from nature; it is perfected, however, by art, and through use and exercise it receives perfection: just as also Victorinus very well says, that nature makes one capable, art makes [one] skilled, use however makes [one] powerful: thus indeed by nature all arts and all sciences are perfected. And from this it is, that art imitates nature.
And just as Hesiod says: Some are perfect and good in such things through nature alone; others, however, not by nature, but because teachers of such things place them in the mind; and these become good by placing such things in the mind, through the comprehension of the principles of art and science. Some, however, are so mistaken that they have none of these things in themselves, nor are they able to receive them from others—whom Hesiod considers useless for knowing the true and the good.
It is therefore clear that logic is one of the special sciences, just as in the mechanical [art] in which the special science is the art of making a hammer: whose use, however, is applied to all things which are made by the art of the smith.
For investigation, or reason investigating the unknown through the known, is something special, which has properties and differences and parts and principles: which, when proven concerning it, art and science become special, whose use afterward is applied to all sciences.
Thus therefore it is clear, that logic, generally spoken, is a special science, about which now it is to be treated.
De Praedicabilibus, Bk. I, Tr. I, Ch. 2
This science, which is the method of all philosophy, some assert to be no part of philosophy, saying that there are only three parts of philosophy, namely Physics, Mathematics (or disciplinary), and Metaphysics (or divine). Since a definition stating what and why is the middle in science, and a definition cannot vary except in three ways—namely, that it either conceives of sensible matter, which is with motion and change; or it conceives of intelligible matter, whose essence is not with motion and change according to reason, although according to existence it is in matter which is with change and motion, such as magnitude and number; or it conceives of neither sensible matter according to essence nor according to existence—it seems that philosophy has only three essential parts, as Aristotle also seems to say.
Because of which, some say that logical or rational science is no part of philosophy. They also add in confirmation of their assertion, that the method of a thing does not enter into the division of the thing whose method it is. But it is evident that logic, generally spoken, is the method of philosophy. Therefore, it does not seem to fall into the division of philosophy, nor does it seem to be contained in any part of that genus which is philosophy.
But this opinion certain others, opposing, say: general philosophy is the intention to comprehend the truth of all beings whatsoever, as far as it is possible for man to comprehend it through reason and understanding. But these things are said to be either from our own action—whether by will or by intellect seeking knowledge—or from nature generally so called, which cannot be caused by our action. And since those things which are from nature are causes of our science, and we are not causes of them, there can be no practical science about them. It remains, therefore, that concerning such things there is for us only contemplative science, which is perfected by the light of understanding.
But of those things of which we are the cause by will, there can be for us no speculative science, but only practical science. For the same are in any knowable thing the principles and causes and elements of knowing, which are the principles of being: for otherwise it would follow that that which is known by us is not known according to what it is, but rather would be known according to what it is not. And so, everything known would be falsely known—which is absurd.
It follows, therefore, that about things caused by nature there cannot be science through things which are from us, but rather science of them is had from principles causing their essence and existence in nature, which are only through contemplation in all cases.
Of those things, however, which are from us, there can be no true science for us except through those principles which are in us, through which we are the cause of those things which are from us: whose end is not the true, but the good—what is good for us.
Likewise, therefore, one intention of philosophy will be to comprehend the truth of what is in us, according to the reason by which it seeks to comprehend the truth of that which, by the guidance of reason, is the path toward all knowledge of all things, the knowledge of which arises in us through those things which are known to us, from which we set out to the knowledge of unknowns.
There will be, therefore, from the intention of philosophy also logical science, which is rational.
Furthermore, they say this is shown by the fact that among the Peripatetics, philosophy in its first division is divided into three parts: namely, physics generally so called, ethics generally so called, and rational [philosophy] similarly so taken.
I say “physics generally so called” because it includes both natural [philosophy] and disciplinary [mathematics] and divine [metaphysics]. Ethics generally so called, which includes monastic, economic, and civil [philosophy]. Rational generally, which includes every mode of proceeding from the known to the unknown in whatever way: which takes place through many kinds of proofs, as will be shown in what follows.
It is manifest, therefore, that logic is some part of philosophy.
Furthermore, if something pertains to the intention of philosophy, then this will especially pertain to the intention of philosophy: that without which no one in philosophy can arrive at any knowledge. But one ignorant of logic cannot acquire perfect knowledge of the unknown, because he does not know the method by which one must proceed from the known to the knowledge of the unknown. It seems, therefore, that logic especially pertains to the intention of philosophy.
This dispute, however, Avicenna and Alfarabi say is frivolous and unproductive. Frivolous indeed, because in contradicting each other they do not refer their intention to the same thing said in the same way. For those saying that logic is not a part of philosophy call philosophy “real” and “contemplative.” But those contradicting them and saying logic is a part of philosophy call philosophy the comprehension of all truth, however it may exist—whether in itself, or in us who know or act.
And so they argue frivolously, not referring their intention to the same thing. This dispute is also unproductive, because nothing of the question is explained by the intention. And thus it helps nothing toward the matter at hand.
Logic, therefore, is one of the parts of philosophy generally so called, which seeks to comprehend the truth in a marvelous way, according to the mode by which it is possible to comprehend it from the proper principles of the thing admired.
For this varies according to the properties of each science. Just as in real philosophy the variation of philosophy corresponds to the diversity of mediation (which is the middle in demonstration), so in logics or rational sciences, according to the variations of reasoning, science is varied—that is, the mode of knowing.
For if reason proceeds from signs producing presumption, there will be one part of general logic which is called rhetoric. If, however, it proceeds from fictions causing delight or aversion, there will be another part of logic which is called poetics. If it proceeds from common probabilities, which are found in most cases, there will be another part which is called dialectic. If it proceeds from essential and proper causes, there will be another part called demonstrative. If it proceeds from things that seem and are not, there will be another part called sophistical. If it teaches how to proceed through tricks provoking the responder, there will be another part of general logic called tentative. And thus, it is easy to understand about all the others.
Of these things which have been said, Avicenna gives the reason, saying that all things are to be received in three ways: first, as they are in the principles of their essence; second, in the existence they have in individual subjects; third, as they are received in the intellect.
For many things, according to the principles of their essence, are separate from motion and matter, which yet according to existence are or can be in motion and matter—such as substance, unity, identity, multitude, and diversity, and other such things, which indeed in their essential principles are ungenerated and incorruptible. And in this way, according to Plato, they are the formal principles of things; for this reason Plato says such things are ungenerated and incorruptible.
And if such things are said to be generated or corrupted, this is only accidentally—that is, according to the existence they have in generated and corruptible things. The reception of things according to the existence they have in supposits will be according to the existence of those supposits, and according to the definition they may have according to the existence they have in them.
The reception of things, however, as they are in the intellect, is according to the knowledge they have—not as they are in themselves, but as they are received by the intellect.
And according to all these three modes there are also consequent accidents, which are properly called the passions of the thing itself. And thus, in each of these three modes, philosophy intends to acquire the truth about them. And this is through some guidance of reason, which pertains to logic.
For things as they have existence in the soul have proper accidents, such as something being known by man and something being unknown. And when compared with each other they are united in some way, there will be a path of reason—proceeding from the known to the unknown, through comparison of the known to the unknown, according to the agreement or difference of the known with the unknown.
From which it is understood that one is composed with another and is predicated of it, or one is divided from another and is removed from it: for by this mode one comes from one to another.
Therefore, in this way, logic pertains to the intention of general philosophy.
De Praedicabilibus, Bk. I, Tr. I, Ch. 3
Extremely moreover necessary and useful is logic to philosophy. Since indeed logic teaches how the unknown becomes known, it is clear that in no philosophy can anything become known except through the faculty of logical doctrine.
It is, as Boethius says in the Zopici, the reason of discoursing, that is, teaching how about anything one ought to discourse, which, into two, as he says, is divided parts: the science of finding, which the Greeks called Topics; and the science of judging, which the Greeks called Analytics, the Latins however named Resolutive.
It is established, moreover, that without discourse and inquiry one does not come from the known to the unknown. This discourse is nothing other than inquiry discoursing how the known is compared to the unknown, how it is related to that—as cause, or principle, or sign, or conjecture to it; or in a contrary way, as opposed to it—without which in no science can anything be known.
With respect to this, therefore, that science is teaching to discourse about every matter, it is not only useful in itself, but also necessary to everything which we intend to know.
Because of which Aristotle frequently says in various of his books, that the cause of the error of the Ancients was that they had not found or possessed the science of logic.
For logic teaches the principles—how, and with what principles, and with what arguments—about any knowable thing one must discourse. This method, unless it be known, the knowable cannot be found, because he who seeks the method of finding the science of a given knowable does not have the reason why.
Aristotle also says that the method of knowing must be learned before any science, so that through that method the science of any knowable may be found.
Since indeed science is a habit of conclusion, it is necessary that he who receives science know how to conclude. But he does not know how to conclude who does not know what he ought to conclude. And since nothing ought to be concluded except a question, it is necessary that he know what and how to ask that which is intended to be concluded.
Moreover, he does not know how to conclude who does not know from what things, and of what kind, and to what conclusion it must be concluded.
All these things, however, no philosophy teaches except only logic. Therefore, it is not only useful and supporting to all sciences, but also necessary.
Because of which, those not knowing logic—even what they seem to know—they do not know that they know, because they do not know how the science of discoursing about anything has been acquired.
Moreover, the one not knowing logic, even if he seems to know something, does not know, as we said above, since he does not know the reason of what he knows. And he is related to the known and to the act of knowing just as fire is to burning wood.
And therefore, it belongs to the one who knows (as Aristotle teaches in the First Philosophy) to be able to teach. But he cannot teach who does not know how to explain the reason of what he knows.
But he does not know how to explain the reason of what he knows who does not know the causes and principles of logic. Such a one, therefore, even in those things which he seems to know, is like an uneducated man compared to one who is literate.
Such a one also detects neither his own error nor that of another, because he does not have the habit by which he may judge whether he rightly knows what he knows, or not rightly.
Moreover, because the science of discovering anything known is through relations of one to another, which are called topics or places, by which the intellect or opinion or faith or estimation or suspicion is placed in another, which already is held within in the soul of the inquirer.
Without logic, one can proceed neither to inquire nor to discover anything; nor even, when what was sought is found, can it be known whether it has been found or not.
It is therefore clear, even with respect to this, that logic is not only useful, but also necessary to all philosophy.
Moreover, even because it is a science of judging (since that which has been found is judged whether it has been rightly known through its principles), logic is necessary to all philosophy.
This logic teaches in two ways: teaching to resolve what is known into principles—namely, of consequence, which are in the figures and modes of syllogistic consequences; and into the real principles of that which follows, as into immediate and essential causes, and convertible with that which is known through the conclusion—by which judgment everything that is known is, as it were, weighed, reducing to the balance of reason everything which in all the natural sciences is sought to be known.
This science is not only necessary, but also useful, just as the good is the happiness of man according to the most perfect act of the best part of man’s soul—that is, according to the contemplative intellect.
Nor can the intellect contemplate unless it knows the principles of contemplation, and knows how to discover what it seeks to contemplate, and judge that very thing which it already contemplates as found.
The conclusion is clear: that before all [others], this science is useful for happiness—without which the act of happiness is not attained, and through which the happy person receives the act of operation without hindrance.
For this science frees from phantasms (which seem and are not), condemns errors, reveals falsehoods, and gives the light of right contemplation in all things.
Before all others, therefore, this science is to be considered.
De Praedicabilibus, Bk. I, Tr. I, Ch. 4
Since moreover logic is a contemplative science, teaching how, and through what, one comes through the known to knowledge of the unknown, it is necessary that logic be about this kind of instrument of reason, through which knowledge of the unknown is acquired through the known, in everything in which from the unknown the known is made.
But this is argumentation, insofar as argumentation is reasoning that convicts and convinces the mind through the relation of the known to the unknown, about the knowledge of the unknown.
Among the species of argumentation, the principal is the syllogism. Because of this, some have said that the whole of logic is about the syllogism and the parts of the syllogism—determining the common subject of logic according to what is the principal subject.
For not about everything can there be knowledge through syllogism, because syllogistic discourse is only from the universal accepted universally—which in many sciences cannot be, as in rhetoric, because in those chiefly local relationships are considered, from which through enthymemes is concluded what was sought.
Since therefore logic, as Aristotle says, gives to every science the method of discoursing, and of finding, and of judging what is sought: it must be about such a thing as its subject, which is equally applicable to all in everything.
There are also certain things in which from singulars we seek to find what is unknown, as in experimental sciences, in which we use either syllogism or induction to accept the universal, and we cannot use a perfect syllogism. Because of this, syllogism cannot be the common subject of logic.
Because of this also, in logical writings of the Ancients, not only is it taught what the syllogism is, and how, and from what it is made: but here also is taught what argumentation is, and what are its parts and species.
There are, however, some who interpret logic as the same as sermocinal [linguistic], saying that general logic is the same as sermocinal science, under which they say are contained poetry, rhetoric, and that which they call dialectic. And so they say the subject of general logic is speech, insofar as it is according to grammar, signifying things which are signified through it.
This opinion Avicenna opposes, saying that speech by itself signifies nothing: for if it signified something by itself, it would always and for everyone signify that thing—which is false. Signification therefore it receives from the convention of the institutor. It therefore signifies only insofar as it is conceived in the intellect of the institutor.
But such speech (insofar as it is thus significative of a concept) man uses toward himself and toward another. Because of this Damascene says that it is divided in two—namely, into the inner speech, that is, speech disposed inwardly in the mind; and into that which is from signs, which the angel is in understanding, the messenger of his heart, because it announces the concept of the heart to another.
Because of this, the logician uses speech both toward himself and toward another accidentally, and not essentially: because without significative speech he cannot proceed to knowledge of that which is unknown. But reasoning he uses essentially to make known that which has been declared.
Because of this, since the intention of the logician is to teach those things through which one comes essentially into the knowledge of the unknown by means of the known, the subject of logic is argumentation: because through argumentation that which is intended is accomplished.
Further, incomplex speech, although it designates something in the simple intellect, nevertheless it does not make belief whether something is or is not, because it does not signify something to be or not to be.
But one does not come to the knowledge of the unknown except through something that makes belief about the unknown—that it is or is not. Therefore, incomplex speech cannot be the instrument through which the intellect is led to knowledge of the unknown—which is what the logician principally intends.
Therefore, incomplex speech is not assumed by the logician except accidentally, insofar as it is a part of complex speech, which is designative of the composite intellect.
Moreover, complex speech, inasmuch as it is complex, does not signify being or not being. For if it did, every complex speech would signify the thing to be or not to be; and thus imperative, or optative, or subjunctive speech would signify the thing to be or not to be—which is false.
Therefore, complex speech, through this—that it is enunciative—signifies the thing to be or not to be. But through this—that it signifies the thing to be or not to be—it does not have the power to argue and to make belief about the enunciated.
Therefore, through this—that it is enunciative—it is not the instrument through which the logician attains what he intends. It makes belief, however, through this—that it is collective according to the form of argument.
Argumentation, therefore, is the instrument of the logician. But general logic is that which teaches about this as about its subject, by which the logician, using it, comes into science of the unknown through the known. Therefore, argumentation is the proper subject of the logician teaching logic.
And this is the opinion of the three philosophers: Avicenna, Alfarabi, and Algazel.
All sermocinal sciences, however, use speech—namely, grammar, poetry, rhetoric, and that which is called logic.
Grammar, insofar as it is the mode of inflections and constructions, exists as designative of the simple and complex intellect simply, without knowing about the signified whether it is or is not.
Poetry, however, uses it insofar as the uttered rhythm provokes the hearer by delight or revulsion to do or avoid something; because of which, from various compositions and according to metalepsis or fable, it invents fabrications intended to provoke listeners.
Rhetoric, however, uses speech insofar as it is designative of that by which it intends to persuade.
But the logician alone uses speech insofar as it is part of the instrument by which belief is made about the unknown, when knowledge of it from the known is argued through the structure of the argument.
Therefore, he uses speech for the sake of something else, and not for its own sake.
The proof of this is that the known (through which knowledge of the unknown is received) is considered in two ways: namely, insofar as it is a thing received outside the soul of the knower, and insofar as it is a notion in the soul of the knower.
It does not make knowledge of the unknown as it is the thing received outside the soul of the knower, but rather as it is the notion of the thing existing in the soul of the knower. For thus it is significative and inferential of that which is unknown, which the intellect perceives in some way with complete understanding.
In this way, therefore, the logician considers the meaningful words of things—and not otherwise.
I say “with complete understanding” because there are perhaps some so perceptive that from the understanding of one complex word they immediately form belief about the unknown. But this is imperfect and not general. And therefore it does not suffice, but there is need for argumentation to accomplish this perfectly.
If, however, someone asks whence that thing becomes known, from which knowledge and belief of the unknown is received, this is to ask nothing: because in each person something is known of itself and implanted by nature, through which he can receive knowledge of the unknown. Otherwise, man would be perceptive of no science or discipline, just as a brute animal is not—if the first principles of knowing were not naturally in man of themselves.
Therefore, about argumentation or syllogism, logic is entirely [concerned] as about its subject. But about other words—incomplex ones—it is [concerned] on account of that [i.e., argumentation].
De Praedicabilibus, Bk. I, Tr. I, Ch. 5
The division of logic, and what are its parts, as Avicenna and Alfarabius say, are to be taken from its intention. As was already said before, logic intends to teach the principles through which, by means of what is known, one can come into knowledge of the unknown.
There is the incomplex thing, about which it is asked what it is; and the complex thing, about which it is asked whether it is true or false.
But the incomplex, about which is asked what it is, cannot be known except through definition. The complex, however, about which it is asked whether it is true or false, cannot be known except through argumentation.
These, therefore, are two parts of logic: one, namely, so that the principles are taught by which the definition of the thing and its quiddity may be known—so that through those principles it may be taught what is the true definition of the thing, and what is not, and what may seem to be and is not.
The other part is so that the principles are taught of how, through argumentation, the truth or falsity of the enunciation is proven—and so that the form of that argumentation is taught, with respect to figure and mode, and arrangement or composition; and so that the matter of the same argumentation is taught; and so that it is taught what seems to be argumentation and is not, because it has some appearance but has no true reality.
And so that cautions are taught by which the opponent or respondent is in some way hindered or disturbed from conjecturing the truth, or so that he may perfectly see the truth and not turn away from it.
But the first of these parts either was not handed down by the Ancients, or it has not reached us. This part, also, Avicenna and Alfarabius say did not reach the Arabs.
Nevertheless, Aristotle says in many places that this was the cause of error for the Ancients: because they did not have the art of defining. That some say Aristotle handed this down in the sixth book of the Topics is frivolous: for there he did not hand down the part of defining, but he teaches to resolve the problem in which is asked what lies within, as a definition.
Also, some others say that these things belong to metaphysics, and that Aristotle handed them down in the seventh and eighth books of the First Philosophy: but this is absurd.
For there Aristotle teaches what are the definients of both substance and accident, and what is the physical definition, and how a definition is one and not many, and other such things.
But how, by defining, one answers the question by which it is asked what a thing is through its essence and quiddity, he does not teach: because this pertains to logic, and not to first philosophy.
It is therefore clear that this part has not yet reached us. There are also subdivisions of these parts which logic carries out, of which in what follows there will be treatment.
And because logic considers all things insofar as they are in the soul or in the intellect of him who seeks to come through the known into knowledge of the unknown, for the sake of these it considers the word signifying by convention—and what and how it signifies.
Which the earlier Peripatetics (as Alfarabius and Algazel say) distinguished in five ways:
First, and principally, a word signifies that to which it was by first institution established to signify: as “man” signifies man, and “house” house, and so with others.
Second, a thing is said to be signified that is consequentially implied in the word itself: as “house” signifies foundation and wall, and any integral whole in this way signifies its integral and principal parts.
Third, when the thing accompanies the meaning of the word: as if there is a wall, it signifies that the foundation exists; and if there is a roof, it signifies that the foundation and wall exist.
Fourth, when one thing is in the intellect of another: as “man” signifies “animal” and “rational.” And to this mode is reduced the fact that an accident or passion signifies a subject: as “snub-nosed” signifies “nose,” and “white” signifies “bounded body,” and others of this sort.
Fifth, as opposition signifies opposition, and an opposite signifies an opposite: as separation from white signifies aggregation of black, and motion toward the center of the cold signifies motion from the center of the hot, and other things of this sort.
And this pertains to logic, because logic is the science of reasoning. But reasoning, as Aristotle says, cannot take place unless it is given that names signify something—because they do not signify infinitely.
For the sake of this, also, logic considers common things and incomplex words.
But complexity and incomplexity do not belong to the thing as thing, nor to the word as word, but belong to the word insofar as it is referred to the simple or composite intellect.
By “simple” I mean the intellect which is the intuitive grasp of one thing. For such an intellect is not signified to another except by incomplex word or speech.
By “composite” I mean the intellect which takes one thing in another or as divided from another. This intellect cannot be designated by incomplex word, but rather by complex: as “man is an animal,” or “man walks,” or “man is not a stone,” and the like.
Because of this, defining the incomplex, the ancient Peripatetics said that an incomplex signifying word by convention is that whose parts signify nothing of the whole’s intention: as when “man” is said, the part “ma-” and the part “-n” signify nothing of the intention of “man.”
And even if a name of some simple thing is itself composite, as “Adeodatus,” still, insofar as it is the name of a single simple thing, it is incomplex speech. And what I say in “Adeo” and what I say in “datus” signify nothing of the intention of the whole named by the name “Adeodatus.”
But complex speech is that whose parts signify something of the intention of the whole, as when we say “man walks”: both the word “man” and the word “walks” signify something of the intention of this complex expression.
Furthermore, a word, insofar as it is referred to the intellect of the one who seeks to find the unknown through the known, has that it is divided into the common or universal and the proper or singular. For nothing of this sort comes to it insofar as it is referred to the designated thing.
All things are singular which fall under the senses and are constituted by nature; and the common which is in them is taken by the intellect. And therefore, Aristotle and Boethius say that the universal is while it is understood, and the singular while it is sensed.
The common, however, which is in them, is threefold:
That which is actually in many, as “man,” which is actually divisible into many, so that the whole is in individuals by nature and reason.
That which is actually in one, but by aptitude of nature can be in many, as “sun.”
And that which is actually in none, nor in any one individual, but by aptitude does not contradict and by reason can be in many—as the heptagon. If we suppose that the heptagon is nothing in actuality, still by aptitude it is and can be in many.
And to speak generally: every name or word that is imposed from a form communicable to many, whether that form is accidental or substantial, is common and universal—whether it is actually communicated to many or not.
But the proper or singular is that which is imposed from an accidental form signifying a collection of accidents that cannot be found except in one alone, as “Socratity” or “Platonity,” which, from subject parents and place of birth and such things, can belong only to one and it is impossible to find in another.
And this is done in two ways: either through a proper name or through a gesture of demonstration to this singular, as when we say “this wood” or “this white thing”: for “this” is so “this” that it cannot be another.
Furthermore, a word or significant voice is articulated—not from this that it is referred to the designated thing, but from this that it is in the intellect of the one seeking to know the unknown through the known.
Although even this word is either noun or verb. The pronoun (as its name testifies) is taken in place of the noun in supposition. And the participle, with the supplement of the verb “to be” in addition or in predication, supplies the place of the verb: as when we say “man is loving,” or “man loves,” or “man is loved,” or “man has loved,” or “man will be loving,” or “man will love.”
The other parts, however, which are indeclinable, have no meaning without additions: as if one says “man is,” nothing is understood unless it be added “in what he is,” as “in the house.” Likewise, when one says “man is above,” and does not add “above what”; or if one says “man however,” and does not add to whom the conjunction is opposed; or if one says “man therefore,” unless it is added what is inferred.
The noun, however, as will be had in what follows, is significative by convention without time. The verb, however, with time which is subjected to it, is predicated, or said, or denied, or affirmed of one.
Furthermore, to the word significative by convention, insofar as it is in the intellect of the one seeking knowledge of the unknown through the known, there belong five things: namely, that it be univocal, and some are diversivocal, some multivocal, some equivocal, some analogical or proportional, which are called among the Arabs convenientia.
Univocal are those which are imposed from such a form to which all that participate in it relate in one way in reality and reason, without more or less: as “animal” is participated by species of animals, and “man” by individuals under it.
Diversivocal are different names of one and the same thing according to substance: because the institutor of those names, in instituting, was affected by different properties of the thing—like ensis, mucro, spata, gladius, vestis, tunica, and such things.
Multivocal are different names of different things: because the institutor, being affected by different properties of different things, instituted various names—like equus and asinus.
Equivocal are when one name is imposed on different things according to different meanings: because one property found in different things affects the institutor—but that property is not in those things by one meaning. As “canis” (dog) is a name imposed on the barking animal, and the celestial star, and the sea fish, because of one property found in them—which is that all these are biting things—even though they are not biting in the same sense.
Analogous, however, are those said proportionally, as the Arabs call them convenientia, and they are intermediate between univocal and equivocal, which are imposed on different things according to being and substance, by relation to one thing to which they are proportioned.
As “being” (ens), which is said of substance first and principally, and of accident secondarily, because it is something of being. And “quantity” is said to be a being because it is a measure of being. And “quality” is said to be a being because it is a disposition of being.
And this, as John Damascene says in his logic, happens in three ways:
by proportion to one subject, as ens;
by proportion to one efficient agent, as “doctor” is truly called doctor who operates medicine by that which is in him; and a doctor is called an idiot, imitating the doctor through experience or experiments in the operation of medicine, and not through the art of medicine in him;
and “doctor” is said of an instrument of medicine through which medication is made, as syringe, or bottle, or something like that.
Third, by proportion of the same, as “healthy,” which principally consists in the equal complexion of animals, and is in food as preserving that same health, and in urine as indicating it, and in air or place as fostering it—and so with others.
All these things have been extracted from the logicians, because they pertain to the significant and articulate word, according to how it affects the intellect of him who seeks to be made certain about the unknown by the known.
For we wish, according to the custom which we have in other matters, to set down everything, as much as we can, which pertains to the illumination of doctrine.
De Praedicabilibus, Bk. I, Tr. I, Ch. 6
From these things which have been said, it is clear that if someone seeks to know the incomplex which is unknown, through that which cannot be unknown to him, he cannot find knowledge of it except through definition or something else which imitates the definition of the incomplex by some declaration.
Of this, the principles and rules are five, and five are the corruptions.
The first, indeed, is that all things placed in the definition are substantial and substantially existing in the defined thing: because definition is called that which limits all boundaries of essence, joins and unites, and explains what are the principles of the defined or the being of the defined, namely the essence, the power, and the ultimate act completing the being of the defined—just as we say “rational animal, mortal, voluntarily mobile” is the definition of man.
“Animal,” moreover, inasmuch as it includes in itself an animated sensible body and substance, is the first power in which the being of man is begun. But this beginning through “rational” is determined essentially to the act of reason. Through “mortal,” however, it is determined to the species, especially according to the Stoics, who said “good spirits” and “evil spirits” are rational animals, aerial bodies, and of immortal life—as Themistius and Apuleius say.
Through “voluntarily mobile” it is separated from other things which are apt by nature and imagination for motion. And this is the first.
The second, however, is (as Aristotle teaches in the Metaphysics) that the ultimate difference be convertible with the defined—which makes the whole definition to be convertible: just as “voluntarily mobile” is converted with “man,” inasmuch as “will” denotes appetite which is in reason.
The third, however, is that the prior placed in the definition relate to the following, as proximate power to act, and as determined to determinative, and as distinct to distinguishing—just as “animated” to “sensible,” and “sensible” to “rational,” and “mortal” to “rational,” and “voluntarily mobile” to “mortal”: so that in one motion of generation always the later proceeds from the former.
The fourth is that the first defining term be per se known to him who seeks to know the defined, both in substance and in power; because unless it is known in substance, it cannot be a principle of the knowledge of the unknown; and unless it is known in power, the definition of what is sought to be known cannot be hunted through its division.
The fifth, however, is that the definition state the whole being of the defined: because otherwise it would not reach from end to end in the quiddity and being of the defined, and so would not have the true name of definition.
And through this the definition has that it is one and not many—just as motion is one and not many, which is from first power through a middle path unto the ultimate act.
These things, therefore, considered in a defining way, make such a definition that truly and wholly certifies the defined.
The faults of it are also five, opposed to these, although each of the faults exists in many ways: just as in other things in which the good is made from one thing and cause, but evil from many directions and infinite ways, as Pythagoras says.
The first, therefore, fault is, if through one accidental or through several or all accidentals, the essential knowledge of the defined is sought—just as if I say that man is a laughing animal, or that the sun is (as Empedocles says) a white and hot thing.
The second fault is, if the last difference is not convertible: then the preceding things, which are in greater number, are not determined through the ultimate difference to the being of the defined except in potency; nor is the quiddity and being of the defined known through them in universal science, but in potency, not in act—and so the being of the defined is not perfectly known.
The third fault is, if those things which are placed in the definition are placed out of order: for thus act would be signified to precede power in the same thing—which never happens in any being of the defined in which there is both power and act.
In all such things, power immediately precedes act: and therefore, through such a definition, the being (as it is) of the defined would not be declared. And an example of this is if I say that man is living, rational, sensible.
The fourth fault is, that the first defining term is not per se known in substance and power. And this happens in four ways: because when something is defined through what is the same, or through what is equally unknown, or through what is more unknown than it, or through what cannot be known except through the defined, or through what is known by another.
By what is the same: an example is, when time is defined as the measure of motion—for what is said of time is said of the measure of motion, because time is nothing else but the measure of motion, and he who is ignorant of time is ignorant of what the measure of motion is.
When it is defined by what is equally unknown: this is as when whiteness is defined through what is contrary to blackness—for equally unknown is what whiteness is, and what its contrary is, namely blackness. And so with the definition of relatives through each other, as will be clear below in the following.
About what is more unknown: an example is, as one who defines fire saying that fire is a thing among bodies most similar to spirit or soul—for he defines fire through soul, which is more unknown than fire in substance and definition.
About that which is defined through what cannot be known except through the defined: an example is, as one who defines the sun saying that the sun is a planet which by its illumination makes the day. Since day is the stay of the sun’s light upon our hemisphere, it is clear that the illumination of the day is known through the defined; and so the definition would be circular, which is highly improper.
All these agree in one, namely that a thing is defined through what ought to be known by another; and so it will never stand, but is always defined through another, and it proceeds to infinity.
The fifth fault is that the definition does not state the whole being of the defined: for if it did not wholly state and explain, it would not say what the being of the defined is, and would not certify the defined except in part.
As one defining triangle says that a triangle is a figure of three angles having three angles equal to two right angles. Since it is not stated in the definition that a triangle is a rectilinear figure having three angles equal to two right angles, it does not say the whole being of the defined: for it could be a figure of three angles having three angles greater than three right angles, if it is composed from arcs—a triangular figure.
Another also fault of cause is in the stated definition: because it states what is not essential to the defined. For having three angles equal to two right angles is not essentially constitutive of the rectilinear triangle, but is a property following the essence of the defined.
Another example of the same (and it is more fitting than that which is stated) is: “a circle is a plane figure contained by one line.” This definition does not state the whole being of the defined: for of that which is the formal principle of the circle, and from which it is produced, it makes no mention—that is, of the center.
Therefore, it will be perfect if it be said thus: “a circle is a plane figure contained by one line, in whose middle there is a point, from which all lines drawn to the circumference are equal, continuously and directly.”
These, therefore, are the things which in definitions are to be attended to and guarded against, if through definition the defined is to be certified.
There are, however, other kinds of declarations—not proper definitions—given sometimes through matter, sometimes assigned only through the efficient cause, which, unless they are reduced to definitions given through genus and essential differences, cannot be called definitions but only certain declarations.
They are reduced in this way: that matter is not taken as simple matter, but insofar as it is first potency to being. For thus it is taken according as in it already is the inchoate essential form, and in whose formal power are inchoately the constituting and distinguishing differences.
As if it is said that man is constituted from body and rational soul: then the body is not taken as separated from form, but rather is said to be animated and sensible, which is the animated sensible, from whose power and beginning is produced the rational.
And so it returns to that definition which is from genus and difference: because an animated sensible body is an animal, and animated with a rational soul is rational.
That which is given through efficient cause is, as if it is said that man is that which is generated from man. Then the agent is not taken as merely efficient, but as agent according to form and univocally.
The univocal agent gives the form according as it passes from formal potency to act. Hence, what is generated from man is not simultaneously alive and animal, nor simultaneously animal and man in act; but first living in act and potentially sensible; second, sensible in act and potentially rational.
And thus the definition given by efficient cause is reduced to that which is from genus and difference. Otherwise, the efficient cause would be of the essence of the defined, and would not certify it.
Any other declaration of the incomplex which is made through accidentals is not a definition but is called a description. Such a declaration, however, ought not to be made through common accidentals, because these are not convertible; but through proper accidentals, because of them it is understood what Aristotle says, that accidentals or knowledge of accidentals contributes greatly to knowing what a thing is.
These are the natural accidents, and they proceed from the aptitude of that very nature, and thus they signify substance—just as often what is prior is known through what is posterior, not simply, but as to us.
This, however, will be made clear in what follows. The logician uses such things in acquiring knowledge of the unknown, just as he also uses other argumentations in acquiring knowledge of the complex, which are less certifying than the syllogism.
The logician, however, uses other declarations whenever they are of greater declaration than the name or incomplex word itself whose knowledge is sought—which, although they do not perfectly certify, nevertheless in some way declare what is sought.
And because, as Ptolemy says, foolish is he who, when he cannot perfectly know what he seeks, throws away that by which he may be able to know something of the sought thing by conjecture.
To give the rules and principles of such things, therefore, belongs to the logician for the cognition of the incomplex—through which, from principles known per se, he may begin and come into knowledge of the things which are sought.
For not all things can be unknown: because thus inquiry would proceed to infinity.
For first principles are, as it were, seeds inserted by nature into the cognition of man, from which, as from seeds, great fruits of sciences arise about those things which are known through them. When the first are posited through division, it is known what power is in them. And also division produces all the way to the end—for which reason the science of division is necessary for the logician, as Boethius says.
De Praedicabilibus, Bk. I, Tr. I, Ch. 7
