The differentia, then, should be distinguished from the genus in this manner. Now seeing it is generally held that if what is musical, in being musical, possesses knowledge in some respect, then also ‘music’ is a particular kind of ‘knowledge’; and also that if what walks is moved in walking, then ‘walking’ is a particular kind of ‘movement’; you should therefore examine in the aforesaid manner any genus in which you want to establish the existence of something; e.g. if you wish to prove that ‘knowledge’ is a form of ‘conviction’, see whether the knower in knowing is convinced: for then clearly knowledge would be a particular kind of conviction. You should proceed in the same way also in regard to the other cases of this kind.
Moreover, seeing that it is difficult to distinguish whatever always follows along with a thing, and is not convertible with it, from its genus, if A follows B universally, whereas B does not follow A universally-as e.g. ‘rest’ always follows a ‘calm’ and ‘divisibility’ follows ‘number’, but not conversely (for the divisible is not always a number, nor rest a calm)-you may yourself assume in your treatment of them that the one which always follows is the genus, whenever the other is not convertible with it: if, on the other hand, some one else puts forward the proposition, do not accept it universally. An objection to it is that ‘not-being’ always follows what is ‘coming to be’ (for what is coming to be is not) and is not convertible with it (for what is not is not always coming to be), and that still ‘not-being’ is not the genus of ‘coming to be’: for ‘not-being’ has not any species at all. Questions, then, in regard to Genus should be investigated in the ways described.
Topics, Book V
Translated by W. A. Pickard-Cambridge
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The question whether the attribute stated is or is not a property, should be examined by the following methods:
Any ‘property’ rendered is always either essential and permanent or relative and temporary: e.g. it is an ‘essential property’ of man to be ‘by nature a civilized animal’: a ‘relative property’ is one like that of the soul in relation to the body, viz. that the one is fitted to command, and the other to obey: a ‘permanent property’ is one like the property which belongs to God, of being an ‘immortal living being’: a ‘temporary property’ is one like the property which belongs to any particular man of walking in the gymnasium.
[The rendering of a property ‘relatively’ gives rise either to two problems or to four. For if he at the same time render this property of one thing and deny it of another, only two problems arise, as in the case of a statement that it is a property of a man, in relation to a horse, to be a biped. For one might try both to show that a man is not a biped, and also that a horse is a biped: in both ways the property would be upset. If on the other hand he render one apiece of two attributes to each of two things, and deny it in each case of the other, there will then be four problems; as in the case of a statement that it is a property of a man in relation to a horse for the former to be a biped and the latter a quadruped. For then it is possible to try to show both that a man is not naturally a biped, and that he is a quadruped, and also that the horse both is a biped, and is not a quadruped. If you show any of these at all, the intended attribute is demolished.]
An ‘essential’ property is one which is rendered of a thing in comparison with everything else and distinguishes the said thing from everything else, as does ‘a mortal living being capable of receiving knowledge’ in the case of man. A ‘relative’ property is one which separates its subject off not from everything else but only from a particular definite thing, as does the property which virtue possesses, in comparison with knowledge, viz. that the former is naturally produced in more than one faculty, whereas the latter is produced in that of reason alone, and in those who have a reasoning faculty. A ‘permanent’ property is one which is true at every time, and never fails, like being’ compounded of soul and body’, in the case of a living creature. A ‘temporary’ property is one which is true at some particular time, and does not of necessity always follow; as, of some particular man, that he walks in the market-place.
To render a property ‘relatively’ to something else means to state the difference between them as it is found either universally and always, or generally and in most cases: thus a difference that is found universally and always, is one such as man possesses in comparison with a horse, viz. being a biped: for a man is always and in every case a biped, whereas a horse is never a biped at any time. On the other hand, a difference that is found generally and in most cases, is one such as the faculty of reason possesses in comparison with that of desire and spirit, in that the former commands, while the latter obeys: for the reasoning faculty does not always command, but sometimes also is under command, nor is that of desire and spirit always under command, but also on occasion assumes the command, whenever the soul of a man is vicious.
Of ‘properties’ the most ‘arguable’ are the essential and permanent and the relative. For a relative property gives rise, as we said before, to several questions: for of necessity the questions arising are either two or four, or that arguments in regard to these are several. An essential and a permanent property you can discuss in relation to many things, or can observe in relation to many periods of time: if essential’, discuss it in comparison with many things: for the property ought to belong to its subject in comparison with every single thing that is, so that if the subject be not distinguished by it in comparison with everything else, the property could not have been rendered correctly. So a permanent property you should observe in relation to many periods of time; for if it does not or did not, or is not going to, belong, it will not be a property. On the other hand, about a temporary property we do not inquire further than in regard to the time called ‘the present’; and so arguments in regard to it are not many; whereas an arguable’ question is one in regard to which it is possible for arguments both numerous and good to arise.
The so-called ‘relative’ property, then, should be examined by means of the commonplace arguments relating to Accident, to see whether it belongs to the one thing and not to the other: on the other hand, permanent and essential properties should be considered by the following methods.
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First, see whether the property has or has not been rendered correctly. Of a rendering being incorrect or correct, one test is to see whether the terms in which the property is stated are not or are more intelligible-for destructive purposes, whether they are not so, and for constructive purposes, whether they are so. Of the terms not being more intelligible, one test is to see whether the property which he renders is altogether more unintelligible than the subject whose property he has stated: for, if so, the property will not have been stated correctly. For the object of getting a property constituted is to be intelligible: the terms therefore in which it is rendered should be more intelligible: for in that case it will be possible to conceive it more adequately, e.g. any one who has stated that it is a property of ‘fire’ to ‘bear a very close resemblance to the soul’, uses the term ‘soul’, which is less intelligible than ‘fire’-for we know better what fire is than what soul is-, and therefore a ‘very close resemblance to the soul’ could not be correctly stated to be a property of fire. Another test is to see whether the attribution of A (property) to B (subject) fails to be more intelligible. For not only should the property be more intelligible than its subject, but also it should be something whose attribution to the particular subject is a more intelligible attribution. For he who does not know whether it is an attribute of the particular subject at all, will not know either whether it belongs to it alone, so that whichever