The Basic Works of Aristotle (Modern Library Classics) (21 page)

27
     A probability and a sign are not identical, but a probability is a generally approved proposition: what men know to happen or not to happen, to be or not to be, for the most part thus and thus,
(5)
is a probability, e. g. ‘the envious hate’, ‘the beloved show affection’. A sign means a demonstrative proposition necessary or generally approved: for anything such that when it is another thing is, or when it has come into being the other has come into being before or after, is a sign of the other’s being or having come into being. Now an enthymeme is a syllogism starting from probabilities or signs,
(10)
and a sign may be taken in three ways, corresponding to the position of the middle term in the figures. For it may be taken as in the first figure or the second or the third. For example the proof that a woman is with child because she has milk is in the first figure: for to have milk is the middle term. Let
A
represent to be with child,
B
to have milk,
(15)
C
woman. The proof that wise men are good, since Pittacus is good, comes through the last figure. Let
A
stand for good,
B
for wise men,
C
for Pittacus. It is true then to affirm both
A
and
B
of
C:
only men do not say the latter, because they know it, though they state the former. The proof that a woman is with child because she is pale is meant to come through the middle figure: for since paleness follows women with child and is a concomitant of this woman,
(20)
people suppose it has been proved that she is with child. Let
A
stand
for paleness,
B
for being with child,
C
for woman.
(25)
Now if the one proposition is stated, we have only a sign, but if the other is stated as well, a syllogism, e. g. ‘Pittacus is generous, since ambitious men are generous and Pittacus is ambitious’. Or again ‘Wise men are good, since Pittacus is not only good but wise’. In this way then syllogisms are formed, only that which proceeds through the first figure is irrefutable if it is true (for it is universal),
(30)
that which proceeds through the last figure is refutable even if the conclusion is true, since the syllogism is not universal nor correlative to the matter in question: for though Pittacus is good, it is not therefore necessary that all other wise men should be good. But the syllogism which proceeds through the middle figure is always refutable in any case: for a syllogism can never be formed when the terms are related in this way: for though a woman with child is pale,
(35)
and this woman also is pale, it is not necessary that she should be with child. Truth then may be found in signs whatever their kind, but they have the differences we have stated.

[70b]
We must either divide signs in the way stated, and among them designate the middle term as the index
¹⁵
(for people call that the index which makes us know, and the middle term above all has this character), or else we must call the arguments derived from the extremes signs, that derived from the middle term the index: for that which is proved through the first figure is most generally accepted and most true.
(5)

It is possible to infer character from features, if it is granted that the body and the soul are changed together by the natural affections: I say ‘natural’, for though perhaps by learning music a man has made some change in his soul,
(10)
this is not one of those affections which are natural to us; rather I refer to passions and desires when I speak of natural motions. If then this were granted and also that for each change there is a corresponding sign, and we could state the affection and sign proper to each kind of animal, we shall be able to infer character from features. For if there is an affection which belongs properly to an individual kind,
(15)
e. g. courage to lions, it is necessary that there should be a sign of it: for
ex hypothesi
body and soul are affected together. Suppose this sign is the possession of large extremities: this may belong to other kinds also though not universally. For the sign is proper in the sense stated, because the affection is proper to the whole kind, though not proper to it alone,
(20)
according to our usual manner of speaking. The same thing then will be found
in another kind, and man may be brave, and some other kinds of animal as well. They will then have the sign: for
ex hypothesi
there is one sign corresponding to each affection. If then this is so, and we can collect signs of this sort in these animals which have only one affection proper to them—but each affection has its sign, since it is necessary that it should have a single sign—we shall then be able to infer character from features.
(25)
But if the kind as a whole has two properties, e. g. if the lion is both brave and generous, how shall we know which of the signs which are its proper concomitants is the sign of a particular affection? Perhaps if both belong to some other kind though not to the whole of it, and if, in those kinds in which each is found though not in the whole of their members, some members possess one of the affections and not the other: e. g. if a man is brave but not generous, but possesses, of the two signs, large extremities,
(30)
it is clear that this is the sign of courage in the lion also. To judge character from features, then, is possible in the first figure if the middle term is convertible with the first extreme, but is wider than the third term and not convertible with it: e. g. let
A
stand for courage,
B
for large extremities, and
C
for lion.
B
then belongs to everything to which
C
belongs,
(35)
but also to others. But
A
belongs to everything to which
B
belongs, and to nothing besides, but is convertible with
B:
otherwise, there would not be a single sign correlative with each affection.

¹
Soph. El.
167
^b
21–36.

²
53
^b
11–25.

³
41
^b
6.

⁴
Cf. i. 32 ff.

⁵
i. e. subject.

⁶
i. e. attribute.

⁷
81.

⁸
66
^b
20–6, 26–30.

⁹
That a man should think the same thing to be the essence of good and to be the essence of bad.

¹⁰
That the essence of good is the essence of bad.

¹¹
The reference may be to
Met.
iv. (Γ).

¹²
ch. 23.

¹³
See note 20.

¹⁴
viz.
B,
thus obtaining a certain premiss
AB,
and a premiss
BC,
on which the inquiry now turns.

¹⁵
This points to the argument in the first figure, whose middle term is a genuine middle term.

   
CHAPTER

  
1.
   The student’s need of pre-existent knowledge. Its nature.

  
2.
   The nature of scientific knowledge. The conditions of demonstration. The meaning of Contradiction, Enunciation, Proposition, Basic truth, Thesis, Axiom, Hypothesis, Definition.

  
3.
   Two erroneous views of scientific knowledge. The futility of circular demonstration.

  
4.
   Types of attribute: ‘True in every instance’, ‘Essential’, ‘Commensurate and universal’, ‘Accidental’.

  
5.
   Causes through which we erroneously suppose a conclusion commensurate and universal when it is not. How to avoid this error.

  
6.
   The premisses of demonstration must be necessary and essential.

  
7.
   The premisses and conclusion of a demonstration must fall within a single genus. The three constituent elements of demonstration.

  
8.
   Only eternal connexions can be demonstrated.

  
9.
   Demonstration must proceed from the basic premisses peculiar to each science, except in the case of subalternate sciences.

10.
   The different sorts of basic truth.

11.
   The function of the common axioms in demonstration.

12.
   The scientific premiss in interrogative form. Formal fallacy. The growth of a science.

13.
   The difference between knowledge of the fact and knowledge of the reasoned fact.

14.
   The first figure is the true type of scientific syllogism.

15.
   Immediate negative propositions.

16.
   Ignorance as erroneous inference when the premisses are immediate.

17.
   Ignorance as erroneous inference when the premisses are mediate.

18.
   Ignorance as the negation of knowledge, e. g. such as must result from the lack of a sense.

19.
   Can demonstration develop an indefinite regress of premisses, (1) supposing the primary attribute fixed? (2) supposing the ultimate subject fixed? (3) supposing both primary attribute and ultimate subject fixed?

20.
   If (1) and (2) are answered negatively, the answer to (3) must be in the negative.

21.
   If affirmative demonstration cannot develop an indefinite regress, then negative demonstration cannot.

22.
   Dialectical and analytic proofs that the answer to both (1) and (2) is in the negative.

23.
   Corollaries.

24.
   The superiority of universal to particular demonstration.

25.
   The superiority of affirmative to negative demonstration.

26.
   The superiority of affirmative and negative demonstration to
reductio ad impossibile.

27.
   The more abstract science is the prior and the more accurate science.

28.
   What constitutes the unity of a science.

29.
   How there may be several demonstrations of one connexion.

30.
   Chance conjunctions are not demonstrable.

31.
   There can be no demonstration through sense-perception.

32.
   Different sciences must possess different basic truths.

33.
   The relation of opinion to knowledge.

34.
   Quick wit: the faculty of instantaneously hitting upon the middle term.

  
1.
   The four possible forms of inquiry.

  
2.
   They all concern the middle term.

  
3.
   The difference between definition and demonstration.

  
4.
   Essential nature cannot be demonstrated.

  
5.
   Essential nature cannot be inferred by division.

  
6.
   Attempts to prove a thing’s essential nature either hypothetically or through the definition of its contrary beg the question.

  
7.
   Definition does not touch the question of existence; demonstration proves existence. Hence definition cannot demonstrate.

  
8.
   Yet only demonstration can reveal the essential nature of things which have a cause other than themselves—i. e. attributes.

  
9.
   That which is self-caused—the basic premisses—is grasped immediately.

10.
   Types of definition.

11.
   The several causes as middle terms.

12.
   The question of time in causal inference.

13.
   How to obtain the definition of a substance. The use of division for this purpose.

14.
   How to select a connexion for demonstration.

15.
   One middle will often serve to prove several connexions.

16.
   If the effect is present, is the cause also present? Plurality of causes is impossible where cause and effect are commensurate.

17.
   Different causes may produce the same effect, but not in things specifically identical.

18.
   The true cause of a connexion is the proximate and not the more universal cause.

19.
   How the individual mind comes to know the basic truths.

1
     
[71a]
All instruction given or received by way of argument proceeds from pre-existent knowledge. This becomes evident upon a survey of all the species of such instruction. The mathematical sciences and all other speculative disciplines are acquired in this way,
(5)
and so are the two forms of dialectical reasoning, syllogistic and inductive: for each of these latter makes use of old knowledge to impart new, the syllogism assuming an audience that accepts its premisses, induction exhibiting the universal as implicit in the clearly known particular. Again, the persuasion exerted by rhetorical arguments is in principle the same, since they use either example, a kind of induction,
(10)
or enthymeme, a form of syllogism.

The pre-existent knowledge required is of two kinds. In some cases admission of the fact must be assumed, in others comprehension of the meaning of the term used, and sometimes both assumptions are essential. Thus, we assume that every predicate can be either truly affirmed or truly denied of any subject, and that ‘triangle’ means so and so; as regards ‘unit’ we have to make the double assumption of the meaning of the word and the existence of the thing.
(15)
The reason is that these several objects are not equally obvious to us. Recognition of a truth may in some cases contain as factors both previous knowledge and also knowledge acquired simultaneously with that recognition—knowledge, this latter, of the particulars actually falling under the universal and therein already virtually known. For example,
(20)
the student knew beforehand that the angles of every triangle are equal to two right angles; but it was only at the actual moment at which he was being led on to recognize this as true in the instance before him that he came to know ‘this figure inscribed in the semicircle’ to be a triangle. For some things (viz. the singulars finally reached which are not predicable of anything else as subject) are only learnt in this way, i. e. there is here no recognition through a middle of a minor term as subject to a major. Before he was led on to recognition or before
he actually drew a conclusion, we should perhaps say that in a manner he knew,
(25)
in a manner not.

If he did not in an unqualified sense of the term
know
the existence of this triangle, how could he
know
without qualification that its angles were equal to two right angles? No: clearly he
knows
not without qualification but only in the sense that he
knows
universally. If this distinction is not drawn, we are faced with the dilemma in the
Meno:
¹
either a man will learn nothing or what he already knows; for we cannot accept the solution which some people offer. A man is asked,
(30)
‘Do you, or do you not, know that every pair is even?’ He says he does know it. The questioner then produces a particular pair, of the existence, and so
a fortiori
of the evenness, of which he was unaware. The solution which some people offer is to assert that they do not know that every pair is even, but only that everything which they know to be a pair is even: yet what they know to be even is that of which they have demonstrated evenness, i. e. what they made the subject of their premiss, viz. not merely every triangle or number which they know to be such, but any and every number or triangle without reservation.
[71b]
For no premiss is ever couched in the form ‘every number which you know to be such’, or ‘every rectilinear figure which you know to be such’: the predicate is always construed as applicable to any and every instance of the thing. On the other hand,
(5)
I imagine there is nothing to prevent a man in one sense knowing what he is learning, in another not knowing it. The strange thing would be, not if in some sense he knew what he was learning, but if he were to know it in that precise sense and manner in which he was learning it.
²