History and Theory of Psychology Course

Paul F. Ballantyne, Ph.D.
pballan@comnet.ca

Selected extracts from: Aristotle's Metaphysics (Book IV, Parts 3-6).

By Aristotle (Translated by W. D. Ross).

BOOK IV, Part 3

....

"Evidently then such a principle is the most certain of all;
which principle this is, let us proceed to say. It is, that the same
attribute cannot at the same time belong and not belong to the same
subject and in the same respect; we must presuppose, to guard against
dialectical objections, any further qualifications which might be
added. This, then, is the most certain of all principles, since it
answers to the definition given above. For it is impossible for any
one to believe the same thing to be and not to be, as some think Heraclitus
says. For what a man says, he does not necessarily believe; and if
it is impossible that contrary attributes should belong at the same
time to the same subject (the usual qualifications must be presupposed
in this premise too), and if an opinion which contradicts another
is contrary to it, obviously it is impossible for the same man at
the same time to believe the same thing to be and not to be; for if
a man were mistaken on this point he would have contrary opinions
at the same time. It is for this reason that all who are carrying
out a demonstration reduce it to this as an ultimate belief; for this
is naturally the starting-point even for all the other axioms.

....

BOOK IV, Part 4

"There are some who, as we said, both themselves assert that it is
possible for the same thing to be and not to be, and say that people
can judge this to be the case. And among others many writers about
nature use this language. But we have now posited that it is impossible
for anything at the same time to be and not to be, and by this means
have shown that this is the most indisputable of all principles.

...

"First then this at least is obviously true, that the word 'be' or
'not be' has a definite meaning, so that not everything will be 'so
and not so'. Again, if 'man' has one meaning, let this be 'two-footed
animal'; by having one meaning I understand this:-if 'man' means 'X',
then if A is a man 'X' will be what 'being a man' means for him. (It
makes no difference even if one were to say a word has several meanings,
if only they are limited in number....

"Let it be assumed then, as was said at the beginning, that the name
has a meaning and has one meaning; it is impossible, then, that 'being
a man' should mean precisely 'not being a man'....

.... [B]ut the point in question is not this, whether
the same thing can at the same time be and not be a man in name, but
whether it can in fact.... Therefore, if it is true to say of
anything that it is a man, it must be a two-footed
animal (for this was what 'man' meant); and if this is necessary,
it is impossible that the same thing should not at that time be a
two-footed animal; for this is what 'being necessary' means-that it
is impossible for the thing not to be. It is, then, impossible that
it should be at the same time true to say the same thing is a man
and is not a man.

....

"Again if when the assertion is true, the negation is false, and when
this is true, the affirmation is false, it will not be possible to
assert and deny the same thing truly at the same time. But perhaps
they might say this was the very question at issue...

....

BOOK IV, Part 5

"From the same opinion proceeds the doctrine of Protagoras, and both
doctrines must be alike true or alike untrue. For on the one hand,
if all opinions and appearances are true, all statements must be at
the same time true and false. For many men hold beliefs in which they
conflict with one another, and think those mistaken who have not the
same opinions as themselves; so that the same thing must both be and
not be. And on the other hand, if this is so, all opinions must be
true; for those who are mistaken and those who are right are opposed
to one another in their opinions; if, then, reality is such as the
view in question supposes, all will be right in their beliefs.

"Evidently, then, both doctrines proceed from the same way of thinking.
But the same method of discussion must not be used with all opponents;
for some need persuasion, and others compulsion. Those who have been
driven to this position by difficulties in their thinking can easily
be cured of their ignorance; for it is not their expressed argument
but their thought that one has to meet. But those who argue for the
sake of argument can be cured only by refuting the argument as expressed
in speech and in words.

"Those who really feel the difficulties have been led to this opinion
by observation of the sensible world. (1) They think that contradictories
or contraries are true at the same time, because they see contraries
coming into existence out of the same thing. If, then, that which
is not cannot come to be, the thing must have existed before as both
contraries alike, as Anaxagoras says all is mixed in all, and Democritus
too; for he says the void and the full exist alike in every part,
and yet one of these is being, and the other non-being. To those,
then, whose belief rests on these grounds, we shall say that in a
sense they speak rightly and in a sense they err. For 'that which
is' has two meanings, so that in some sense a thing can come to be
out of that which is not, while in some sense it cannot, and the same
thing can at the same time be in being and not in being -but not in
the same respect. For the same thing can be potentially at the same
time two contraries, but it cannot actually. And again we shall ask
them to believe that among existing things there is also another kind
of substance to which neither movement nor destruction nor generation
at all belongs.

....

BOOK IV, Part 6:

....

"Let this, then, suffice to show (1) that the most indisputable of
all beliefs is that contradictory statements are not at the same time
true, and (2) what consequences follow from the assertion that they
are, and (3) why people do assert this. Now since it is impossible
that contradictories should be at the same time true of the same thing,
obviously contraries also cannot belong at the same time to the same
thing. For of contraries, one is a privation no less than it is a
contrary-and a privation of the essential nature; and privation is
the denial of a predicate to a determinate genus. If, then, it is
impossible to affirm and deny truly at the same time, it is also impossible
that contraries should belong to a subject at the same time, unless
both belong to it in particular relations, or one in a particular
relation and one without qualification.

Posted: [March, 2008]

Related page:

Aristotelian and Dialectical Logic