Organon. Aristotle

but each principle itself ought to be credible by itself. Probabilities however are those which appear to all, or to most men, or to the wise, and to these either to all or to the greater number, or to such as are especially renowned and illustrious. Moreover a contentious syllogism is one which is constructed from apparent, but not real probabilities, and which appears to consist of probabilities, or of apparent probabilities. For not every thing which appears ​probable is so, since none of those which are called probable has entirely the superficial image (of probability), as happens to be the case about the principles of contentious arguments, since immediately, and for the most part, the nature of the false in them is evident even to those who have small perception. Let then the first of the syllogisms called contentious, be also called a syllogism, but let the other be a contentious syllogism, yet not a syllogism (simply), since it appears indeed to draw an inference, but does not collect one.

      Besides all the above-named syllogisms, there are paralogisms, which consist of things peculiar to certain sciences, as happens to be the case in geometry, and those (sciences) allied to it. For this mode seems to differ from the syllogisms enumerated, since he who describes falsely, neither syllogizes from the true and primary, nor from the probable, for he does not fall into definition, since he neither assumes things which appear to all men, nor those which appear to the greater number, nor to the wise, and to these neither to all, nor to the greater part, nor to the most famous; but he makes a syllogism from assumptions, appropriate indeed to science, yet not from the true, as either by describing semicircles not as they ought to be, or by drawing certain lines not as they ought to be drawn, he produces a paralogism.

      Let then the species of syllogisms, to comprehend them summarily, be those which I have stated, and in a word, to sum up all that have been spoken of, and those which shall be mentioned hereafter, let our definition be so far given, because we do not propose to deliver an accurate description of any of these, but wish merely to run through them briefly, thinking it quite sufficient according to the proposed method, in some way or other to be able to know each of them.

Chapter 2

       Table of Contents

      It will be consequent upon what we have stated to describe to what an extent and for what subjects ​this treatise is useful. It is so for three: exercise, conversation, philosophical science. That it is useful for exercise, appears evident from these, that possessing method, we shall be able more easily to argue upon every proposed subject. But for conversation (it is useful), because having enumerated the opinions of the many, we shall converse with them, not from foreign, but from appropriate dogmas, confuting whatever they appear to us to have erroneously stated. Again, (it is useful) for philosophical science, because being able to dispute on both sides, we shall more easily perceive in each the true and the false; also, (it is applicable) to the first principles of each science, since we cannot say any thing about these from the appropriate principles of a proposed science, as they are the first principles of all, but we must necessarily discuss these through probabilities in the singulars. This however is peculiar, or especially appropriate to dialectic, for being investigative, it possesses the way to the principles of all methods.

Chapter 3

       Table of Contents

      We shall possess this method perfectly when we are similarly disposed, as in rhetoric, medicine, and such like powers; and this is to effect what we choose from possibilities, since neither will the rhetorician persuade from every mode, nor the physician heal, but if a man omits no possibility we say that he sufficiently possesses science.

Chapter 4

       Table of Contents

      First then let us examine of what this method consists. If therefore we assume for how many, what ​kind of, and from what things, arguments are constructed, and how we may be well provided with these, we shall sufficiently gain our point. Now those things are equal and the same in number from which arguments are constructed, and about which syllogisms are conversant; for arguments are constructed of propositions, but the things with which syllogisms are conversant are problems. Now every proposition and every problem shows either genus, property, or accident; for difference, being generic, we must place together with genus. Since however of property, one kind signifies the very nature of a thing, but the other does not signify it, let property be divided into the two above-named parts, and let what signifies the very nature of a thing be called definition, but let the other, according to the common appellation attributed about these, be called property. Now it is clear from what we have said, that according to the present division it happens that all are four, either property, or definition, or genus, or accident. Let however no one suppose that we say that each of these asserted by itself is a proposition or a problem, but that problems and propositions are produced from these. Still a problem and a proposition differ in mode, since when it is thus said, is a pedestrian biped animal the definition of man? and is animal the genus of man? there is a proposition, but if (it should be said), whether is a pedestrian biped animal the definition of man or not? there is a problem. So also in other things. Wherefore with propriety problems and propositions are equal in number, for from every proposition you will make a problem by changing the mode.

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Chapter 5

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      We must describe what definition, property, genus, and accident are. Now definition is a sentence signifying what a thing is: and either a sentence is employed instead of a noun, or a sentence instead of a sentence, since it is possible to define some things which are signified by a sentence. As many however as in some way or other make the explanation by a noun, evidently do not explain the definition of the thing, since every definition is a certain sentence. Still we must refer a thing of this kind to definition, as that the becoming is beautiful; in like manner also whether sense and science are the same or different, since about these definitions, whether they are the same or different, there is a very great discussion. In short, however, all things may be called definitive which are under the same method with definitions, but that all which have been spoken of are of this kind is evident from these (considerations). For when we are able to argue that a thing is the same and that it is different, we shall by the same manner be well supplied with arguments about definitions, since when we have shown that it is not the same we shall have upset the definition. Still what is now said is not converted, since it is not enough to construct a definition to show that it is the same, but for the subversion of definition it is sufficient to show that it is not the same thing.

      ​Property, indeed, is that which does not show what a thing is, but is present to it alone, and reciprocates with the thing. As it is the properly of a man to be capable of grammar, for if he is a man he is capable of grammar, and if he is capable of grammar he is a man; since no one calls property that which may possibly be present with something else, as sleep to a man, not even if it should happen at a certain time to be present with him alone. If then any thing of this kind should be called property, it will not be called property simply, but at a certain time or with reference to something, since to be on the right hand is sometimes a property, but biped happens to be called property with reference to something, as to man with reference to horse and dog; but that nothing which may possibly be present with something else is reciprocally predicated is clear, since it is not necessary if any thing sleeps that it should be a man.

      Genus, however, is that which is predicated of many things differing in species, in (answer to) what a thing is; but let those things be said to be predicated in (answer to) what a thing is, which are fitted to answer the person inquiring what the proposed thing is, as it is adapted to man, when it is asked