按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
knows in a way； this he maintains he does not think at all： but that
is impossible。
In the former case； where the middle term does not belong to the
same series； it is not possible to think both the premisses with
reference to each of the two middle terms： e。g。 that A belongs to
all B； but to no C； and both B and C belong to all D。 For it turns out
that the first premiss of the one syllogism is either wholly or
partially contrary to the first premiss of the other。 For if he thinks
that A belongs to everything to which B belongs； and he knows that B
belongs to D； then he knows that A belongs to D。 Consequently if again
he thinks that A belongs to nothing to which C belongs； he thinks that
A does not belong to some of that to which B belongs； but if he thinks
that A belongs to everything to which B belongs； and again thinks that
A does not belong to some of that to which B belongs； these beliefs
are wholly or partially contrary。 In this way then it is not
possible to think； but nothing prevents a man thinking one premiss
of each syllogism of both premisses of one of the two syllogisms： e。g。
A belongs to all B； and B to D； and again A belongs to no C。 An
error of this kind is similar to the error into which we fall
concerning particulars： e。g。 if A belongs to all B； and B to all C；
A will belong to all C。 If then a man knows that A belongs to
everything to which B belongs； he knows that A belongs to C。 But
nothing prevents his being ignorant that C exists； e。g。 let A stand
for two right angles； B for triangle； C for a particular diagram of
a triangle。 A man might think that C did not exist； though he knew
that every triangle contains two right angles； consequently he will
know and not know the same thing at the same time。 For the
expression 'to know that every triangle has its angles equal to two
right angles' is ambiguous； meaning to have the knowledge either of
the universal or of the particulars。 Thus then he knows that C
contains two right angles with a knowledge of the universal； but not
with a knowledge of the particulars； consequently his knowledge will
not be contrary to his ignorance。 The argument in the Meno that
learning is recollection may be criticized in a similar way。 For it
never happens that a man starts with a foreknowledge of the
particular； but along with the process of being led to see the general
principle he receives a knowledge of the particulars； by an act （as it
were） of recognition。 For we know some things directly； e。g。 that
the angles are equal to two right angles； if we know that the figure
is a triangle。 Similarly in all other cases。
By a knowledge of the universal then we see the particulars； but
we do not know them by the kind of knowledge which is proper to
them； consequently it is possible that we may make mistakes about
them； but not that we should have the knowledge and error that are
contrary to one another： rather we have the knowledge of the universal
but make a mistake in apprehending the particular。 Similarly in the
cases stated above。 The error in respect of the middle term is not
contrary to the knowledge obtained through the syllogism； nor is the
thought in respect of one middle term contrary to that in respect of
the other。 Nothing prevents a man who knows both that A belongs to the
whole of B； and that B again belongs to C； thinking that A does not
belong to C； e。g。 knowing that every mule is sterile and that this
is a mule； and thinking that this animal is with foal： for he does not
know that A belongs to C； unless he considers the two propositions
together。 So it is evident that if he knows the one and does not
know the other； he will fall into error。 And this is the relation of
knowledge of the universal to knowledge of the particular。 For we know
no sensible thing； once it has passed beyond the range of our
senses； even if we happen to have perceived it； except by means of the
universal and the possession of the knowledge which is proper to the
particular； but without the actual exercise of that knowledge。 For
to know is used in three senses： it may mean either to have
knowledge of the universal or to have knowledge proper to the matter
in hand or to exercise such knowledge： consequently three kinds of
error also are possible。 Nothing then prevents a man both knowing
and being mistaken about the same thing； provided that his knowledge
and his error are not contrary。 And this happens also to the man whose
knowledge is limited to each of the premisses and who has not
previously considered the particular question。 For when he thinks that
the mule is with foal he has not the knowledge in the sense of its
actual exercise； nor on the other hand has his thought caused an error
contrary to his knowledge： for the error contrary to the knowledge
of the universal would be a syllogism。
But he who thinks the essence of good is the essence of bad will
think the same thing to be the essence of good and the essence of bad。
Let A stand for the essence of good and B for the essence of bad；
and again C for the essence of good。 Since then he thinks B and C
identical； he will think that C is B； and similarly that B is A；
consequently that C is A。 For just as we saw that if B is true of
all of which C is true； and A is true of all of which B is true； A
is true of C； similarly with the word 'think'。 Similarly also with the
word 'is'； for we saw that if C is the same as B； and B as A； C is the
same as A。 Similarly therefore with 'opine'。 Perhaps then this is
necessary if a man will grant the first point。 But presumably that
is false； that any one could suppose the essence of good to be the
essence of bad； save incidentally。 For it is possible to think this in
many different ways。 But we must consider this matter better。
22
Whenever the extremes are convertible it is necessary that the
middle should be convertible with both。 For if A belongs to C
through B； then if A and C are convertible and C belongs everything to
which A belongs； B is convertible with A； and B belongs to
everything to which A belongs； through C as middle； and C is
convertible with B through A as middle。 Similarly if the conclusion is
negative； e。g。 if B belongs to C； but A does not belong to B；
neither will A belong to C。 If then B is convertible with A； C will be
convertible with A。 Suppose B does not belong to A； neither then
will C： for ex hypothesi B belonged to all C。 And if C is
convertible with B； B is convertible also with A； for C is said of
that of all of which B is said。 And if C is conv