Organon. Aristotle

as of a crow, both animal and bird are the genus, when therefore we say, that a crow is a bird, we also say, that it is a certain kind of animal, so that both genera are predicated of it; likewise also when we say that a crow is a winged biped animal, we say that it is a bird, and thus then both the genera are predicated of the crow, and also the definition of them. This nevertheless does not occur in genera which are not subaltern, since neither when we speak of a vessel, do (we speak of) an animal, nor when (we speak of) an animal, (do we mean) a vessel.

      Not only indeed must we observe whether the genera of the thing proposed, be different and not subaltern, but also in regard to the contrary, since ​if the contrary is predicated in several ways, it is evident that the proposition will be so too.

      It is useful also, to regard the definition produced from the composite, as of a white body and white (i. e. clear) voice; for the property being taken away, it is necessary that the same definition should be left. Now this does not occur in equivocals, for instance, in the things now spoken of, for the one, will be body having such a colour, but the other, will be an audible voice; body, then, and voice being taken away, what remains is not the same in each, at least it would be necessary if white, were synonymous, that what is predicated in each (definition), should be (the same).

      Frequently also in the definitions themselves, the equivocal, which is consequent, escapes us, wherefore, we must look to the definitions. Thus, if any one were to say, that what is significant and productive of health, is that which is symmetrically disposed with respect to health, we must not leave off, but consider what he calls symmetrically, in each, as if the one, were to be of such a kind, as to produce health, but the other, such as to signify, what is the quality of the habit.

      Moreover, (we are to examine) whether they may not be compared according to the more, or similarly, as a light voice, and a light garment, and a sharp flavour, and a sharp voice, for these are neither called light nor sharp similarly, nor one, more than the other. So that the light, and the sharp, are equivocal, for every synonym is capable of comparison, since it will either be predicated similarly, or one more than the other.

      Since however of things heterogeneous and not subaltern, the differences are also different in species, as of animal and science, (for the differences of these are diverse,) consider whether those things, which are under the same name, are the differences of different, and not of subaltern genera, as the acute (is the difference) of voice and magnitude, for voice, differs from voice, in acuteness, likewise also one mass, from another, so that the acute is equivocal, for these are the differences of diverse, and not of subaltern, genera.

      ​Again, (observe) whether of things under the same name, there be divers differences, as of the chroma which belongs to bodies, and of that which is in melodies, for of that which belongs to bodies, the differences are, that which diffuses, and that which condenses, the vision, but these are not the same differences of that which is in melodies, so that chroma is an equivocal word, for there are the same differences of the same things.

      Once more, since species is not the difference of any thing, notice of those which are under the same name, whether one is species, but the other, difference, as bodily clearness is a species of colour, but vocal (clearness) is a difference, since voice differs from voice, in being clear.

Chapter 16

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      Concerning therefore what is multifariously predicated, we must consider it through these and such as these; but the differences we must investigate in the genera themselves with respect to each other, as what difference there is between justice and fortitude, prudence and temperance, (for all these are from the same genus, virtue,) and of those which do not differ very much, one from the other, as in what, sense, differs from, science, since in things which are very different, the differences are altogether palpable.

Chapter 17

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      We must consider similitude in the case of things of different genera, (thus) as one thing is to another, so is another to another, for instance, as science to the object of science, so is sense to the ​object of sense, and as one thing in a certain other thing, so is another thing in another, e. g. as sight in the eye, so is intellect in the soul, and as tranquillity in the sea, so is serenity in the air. But most of all, it is necessary to be practised, in things vastly diverse, for we may easily perceive similitudes in the rest. Besides, we must also consider those things which are in the same genus, whether something identical is present with all, as for instance, with man, and horse, and dog; since so far as something identical is present with them, so far are they similar.

Chapter 18

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      To have considered in how many ways a thing may predicated, is useful for perspicuity, (as any one can better know what he admits, when it is clearly explained in how many ways it may be predicated,) and for the construction of syllogisms against the thing itself, and not (merely) against the name. For when it is dubious in how many ways it is predicated, he who answers, and he who questions, may possibly not direct their attention, to the same thing, but when it is explained in how many ways it is predicated and with what object a person admits it, the questioner would appear ridiculous if he did not frame his argument against this. But it is also useful that we may not be deceived (ourselves) by paralogism, and may deceive another by it, since when we know in how many ways predication occurs, we can never be deceived by paralogism, but we shall know if the questioner does not argue against the same thing, and we ourselves, when questioning, shall be able to deceive by paralogism, except the respondent happens to know, in how many ways predication occurs. Nevertheless, this is not possible in all cases, but when of things multifariously predicated, some are true, but others false; this mode however is not appropriate to dialectic, wherefore a thing of ​this kind, must be altogether avoided by dialecticians, viz. arguing against a name, unless any one should be otherwise incapable of discussing the proposition.

      Notwithstanding, it is useful to discover differences, in order to (construct) syllogisms of the same, and of the different, and also to the knowledge of what each thing is. That it is useful for syllogisms about the same, and the different, is clear; for when we have discovered the difference of the things proposed, of whatever kind it may be, we shall have shown that they are not the same, (and it is useful) for the knowledge of what a thing is, because we are accustomed to separate the proper definition of the essence of each thing, by the peculiar differences of each.

      On the other hand, speculation upon the similar, is useful for inductive reasons, and for hypothetical syllogisms, and for the statement of detinitions. For inductive reasons then, because by the induction of similar particulars, we deem it proper to infer the universal, since it is not easy to form induction, when we are ignorant of similars. (It is useful also) for hypothetical syllogisms, because it is probable that as a thing subsists in one of those which are similar, so also it does in the rest, so that in order that we may discuss any of them sufficiently, we should previously acknowledge, that as a thing is in these, so also is its condition in the subject proposed; but when we have demonstrated that, we shall also have proved the proposition by hypothesis, for we have framed a demonstration, upon the supposition that as a thing is in these, so it is also, in the case of what is proposed. Again, for the statement of definitions (it is useful), since being able to comprehend what in each thing is identical, we shall not be in doubt as to what genus the thing proposed ought to be referred, in definition; for of those which are common, what is especially predicated in (the question) what a thing is, will be the genus; in like manner in those which are vastly different from each other, the contemplation of the similar is useful for definitions, as that tranquillity in the sea, is the same thing as serenity in the air, (for each of them is quiet,) and that a point in a line