Book IX
1
We have treated of
that which is primarily and to which all the other categories of being
are referred-i.e. of substance.
For it is in virtue of the concept of substance that the others also are
said to be-quantity and quality and the like; for all will be found to
involve the concept of substance, as we said in the first part of our
work. And since 'being' is in one way divided into individual thing,
quality, and quantity, and is in another way distinguished in respect of
potency and complete reality, and of function, let us now add a
discussion of potency and complete reality.
And first let us explain potency in the strictest sense, which is,
however, not the most useful for our present purpose. For potency and
actuality extend beyond the cases that involve a reference to motion.
But when we have spoken of this first kind, we shall in our discussions
of actuality' explain the other kinds of potency as well.
We have pointed out elsewhere that 'potency' and the
word 'can' have several senses. Of these we may neglect all the
potencies that are so called by an equivocation. For some are called so
by analogy, as in geometry we say one thing is or is not a 'power' of
another by virtue of the presence or absence of some relation between
them. But all potencies that conform to the same type are originative
sources of some kind, and are called potencies in reference to one
primary kind of potency, which is an originative source of change in
another thing or in the thing itself qua other.
For one kind is a potency of being acted on, i.e. the originative
source, in the very thing acted on, of its being passively changed by
another thing or by itself qua other; and another kind is a state of
insusceptibility to change for the worse and to destruction by another
thing or by the thing itself qua other by virtue of an originative
source of change. In all these definitions is implied the formula if
potency in the primary sense. -And again these so-called potencies are
potencies either of merely acting or being acted on, or of acting or
being acted on well, so that even in the formulae of the latter the
formulae of the prior kinds of potency are somehow implied.
Obviously, then, in a sense the potency of acting and
of being acted on is one (for a thing may be 'capable' either because it
can itself be acted on or because something else can be acted on by it),
but in a sense the potencies are different. For the one is in the thing
acted on; it is because it contains a certain originative source, and
because even the matter is an originative source, that the thing acted
on is acted on, and one thing by one, another by another; for that which
is oily can be burnt, and that which yields in a particular way can be
crushed; and similarly in all other cases. But the other potency is in
the agent, e.g. heat and the art of building are present, one in that
which can produce heat and the other in the
man who can build. And so, in so far as a thing is an organic unity, it
cannot be acted on by itself; for it is one and not two different
things. And 'impotence' and 'impotent' stand for the privation which is
contrary to potency of this sort, so that every potency belongs to the
same subject and refers to the same process as a corresponding
impotence.
Privation has several senses; for it means (1) that which has not a
certain quality and (2) that which might naturally have it but has not
it, either (a) in general or (b) when it might naturally have it, and
either (a) in some particular way, e.g. when it has not it completely,
or (b) when it has not it at all. And in certain cases if things which
naturally have a quality lose it by violence, we say they have suffered
privation.
2
Since some such
originative sources are present in soulless things, and others in things
possessed of soul, and in soul, and in the rational part of the soul,
clearly some potencies will, be non-rational and some will be
non-rational and some will be accompanied by a rational formula. This is
why all arts, i.e. all productive forms of knowledge, are potencies;
they are originative sources of change in another thing or in the artist
himself considered as other.
And each of those which are accompanied by a rational
formula is alike capable of contrary effects, but one non-rational power
produces one effect; e.g. the hot is capable only of heating, but the
medical art can produce both disease and health. The reason is that
science is a rational formula, and the same rational formula explains a
thing and its privation, only not in the same way; and in a sense it
applies to both, but in a sense it applies rather to the positive fact.
Therefore such sciences must deal with contraries, but with one in
virtue of their own nature and with the other not in virtue of their
nature; for the rational formula applies to one object in virtue of that
object's nature, and to the other, in a sense, accidentally.
For it is by denial and removal that it exhibits the contrary; for the
contrary is the primary privation, and this is the removal of the
positive term. Now since contraries do not occur in the same thing, but
science is a potency which depends on the possession of a rational
formula, and the soul possesses an originative source of movement;
therefore, while the wholesome produces only health and the calorific
only heat and the frigorific only cold, the scientific man produces both
the contrary effects. For the rational formula is one which applies to
both, though not in the same way, and it is in a soul which possesses an
originative source of movement; so that the soul will start both
processes from the same originative source, having linked them up with
the same thing. And so the things whose potency is according to a
rational formula act contrariwise to the things whose potency is
non-rational; for the products of the former are included under one
originative source, the rational formula.
It is obvious also that the potency of merely doing a
thing or having it done to one is implied in that of doing it or having
it done well, but the latter is not always implied in the former: for he
who does a thing well must also do it, but he who does it merely need
not also do it well.
3
There are some who
say, as the Megaric school does, that a thing 'can' act only when it is
acting, and when it is not acting it 'cannot' act, e.g. that he who is
not building cannot build, but only he who is building, when he is
building; and so in all other cases. It is not hard to see the
absurdities that attend this view.
For it is clear that on this view a man will not be a
builderunless he is building (for to be a builder is to be able to
build),
and so with the other arts. If, then, it is impossible to have such arts
if one has not at some time learnt and acquired them, and it is then
impossible not to have them if one has not sometime lost them (either by
forgetfulness or by some accident or by time; for it cannot be by the
destruction of the object, for that lasts for ever), a man will not have
the art when he has ceased to use it, and yet he may immediately build
again; how then will he have got the art? And similarly with regard to
lifeless things; nothing will be either cold or hot or sweet or
perceptible at all if people are not perceiving it; so that the
upholders of this view will have to maintain the doctrine of Protagoras.
But, indeed, nothing will even have perception if it is not perceiving,
i.e. exercising its perception. If, then, that is blind which has not
sight though it would naturally have it, when it would naturally have it
and when it still exists, the same people will be blind many times in
the day-and deaf too.
Again, if that which is deprived of potency is
incapable, that which is not happening will be incapable of happening;
but he who says of that which is incapable of happening either that it
is or that it will be will say what is untrue; for this is what
incapacity meant. Therefore these views do away with both movement and
becoming.
For that which stands will always stand, and that which sits will always
sit, since if it is sitting it will not get up; for that which, as we
are told, cannot get up will be incapable of getting up. But we cannot
say this, so that evidently potency and actuality are different (but
these views make potency and actuality the same, and so it is no small
thing they are seeking to annihilate), so that it is possible that a
thing may be capable of being and not he, and capable of not being and
yet he, and similarly with the other kinds of predicate; it may be
capable of walking and yet not walk, or capable of not walking and yet
walk. And a thing is capable of doing something if there will be nothing
impossible in its having the actuality of that of which it is said to
have the capacity. I mean, for instance, if a thing is capable of
sitting and it is open to it to sit, there will be nothing impossible in
its actually sitting; and similarly if it is capable of being moved or
moving, or of standing or making to stand, or of being or coming to be,
or of not being or not coming to be.
The word 'actuality', which we connect with 'complete
reality', has, in the main, been extended from movements to other
things; for actuality in the strict sense is thought to be identical
with movement. And so people do not assign movement to non-existent
things, though they do assign some other predicates. E.g. they say that
non-existent things are objects of thought and desire, but not that they
are moved; and this because, while ex hypothesi they do not actually
exist, they would have to exist actually if they were moved.
For of non-existent things some exist potentially; but they do not
exist, because they do not exist in complete reality.
4
If what we have
described is identical with the capable or convertible with it,
evidently it cannot be true to say 'this is
capable of being but will not be', which would imply that the things
incapable of being would on this showing vanish. Suppose, for instance,
that a man-one who did not take account of that which is incapable of
being-were to say that the diagonal of the square is capable of being
measured but will not be measured, because a thing may well be capable
of being or coming to be, and yet not be or be about to be. But from the
premisses this necessarily follows, that if we actually supposed that
which is not, but is capable of being, to be or to have come to be,
there will be nothing impossible in this; but the result will be
impossible, for the measuring of the diagonal is impossible. For the
false and the impossible are not the same; that you are standing now is
false, but that you should be standing is not impossible.
At the same time it is clear that if, when A is real,
B must be real, then, when A is possible, B also must be possible. For
if B need not be possible, there is nothing to prevent its not being
possible.
Now let A be supposed possible. Then, when A was possible, we agreed
that nothing impossible followed if A were supposed to be real; and then
B must of course be real. But we supposed B to be impossible. Let it be
impossible then. If, then, B is impossible, A also must be so. But the
first was supposed impossible; therefore the second also is impossible.
If, then, A is possible, B also will be possible, if they were so
related that if A, is real, B must be real. If, then, A and B being thus
related, B is not possible on this condition, and B will not be related
as was supposed. And if when A is possible, B must be possible, then if
A is real, B also must be real. For to say that B must be possible, if A
is possible, means this, that if A is real both at the time when and in
the way in which it was supposed capable of being real, B also must then
and in that way be real.
5
As all potencies are
either innate, like the senses, or come by practice, like the power of
playing the flute, or by learning, like artistic power, those which come
by practice or by rational formula we must acquire by previous exercise
but this is not necessary with those which are not of this nature and
which imply passivity.
Since that which is 'capable' is capable of something
and at some time in some way (with all the other qualifications which
must be present in the definition), and since some things can produce
change according to a rational formula and their potencies involve such
a formula, while other things are non rational and their potencies are
non-rational, and the former potencies must be in a living thing, while
the latter can be both in the living and in the lifeless; as regards
potencies of the latter kind, when the agent and the patient meet in the
way appropriate to the potency in question, the one must act and the
other be acted on, but with the former kind of potency this is not
necessary. For the non rational potencies are all productive of one
effect each, but the rational produce contrary effects, so that if they
produced their effects necessarily they would produce contrary effects
at the same time; but this is impossible. There must, then, be something
else that decides; I mean by this, desire or will. For whichever of two
things the animal desires decisively, it will do, when it is present,
and meets the passive object, in the way appropriate to the potency in
question. Therefore everything which has a rational potency, when it
desires that for which it has a potency and in the circumstances in
which it has the potency, must do this. And it has the potency in
question when the passive object is present and is in a certain state;
if not it will not be able to act. (To add the qualification 'if nothing
external prevents it' is not further necessary; for it has the potency
on the terms on which this is a potency of acting, and it is this not in
all circumstances but on certain conditions, among which will be the
exclusion of external hindrances; for these are barred by some of the
positive qualifications.)
And so even if one has a rational wish, or an appetite, to do two things
or contrary things at the same time, one will not do them; for it is not
on these terms that one has the potency for them, nor is it a potency of
doing both at the same time, since one will do the things which it is a
potency of doing, on the terms on which one has the potency.
6
Since we have treated
of the kind of potency which is related to movement, let us discuss
actuality-what, and what kind of thing, actuality is. For in the course
of our analysis it will also become clear, with regard to the potential,
that we not only ascribe potency to that whose nature it is to move
something else, or to be moved by something else, either without
qualification or in some particular way, but also use the word in
another sense, which is the reason of the inquiry in the course of which
we have discussed these previous senses also. Actuality, then, is the
existence of a thing not in the way which we express by 'potentially';
we say that potentially, for instance, a statue of Hermes is in the
block of wood and the
half-line is in the whole, because it might be separated out, and we
call even the man who is not studying a man of science, if he is capable
of studying; the thing that stands in contrast to each of these exists
actually. Our meaning can be seen in the particular cases by induction,
and we must not seek a definition of everything but be content to grasp
the analogy, that it is as that which is building is to that which is
capable of building, and the waking to the sleeping, and that which is
seeing to that which has its eyes shut but has sight, and that which has
been shaped out of the matter to the matter, and that which has been
wrought up to the unwrought. Let actuality be defined by one member of
this antithesis, and the potential by the other. But all things are not
said in the same sense to exist actually, but only by analogy-as A is in
B or to B, C is in D or to D; for some are as movement to potency, and
the others as substance to some sort of matter.
But also the infinite and the void and all similar
things are said to exist potentially and actually in a different sense
from that which applies to many other things, e.g. to that which sees or
walks or is seen. For of the latter class these predicates can at some
time be also truly asserted without qualification; for the seen is so
called sometimes because it is being seen, sometimes because it is
capable of being seen. But the infinite does not exist potentially in
the sense that it will ever actually have separate existence; it exists
potentially only for knowledge. For the fact that the process of
dividing never comes to an end ensures that this activity exists
potentially, but not that the infinite exists separately.
Since of the actions which have a limit none is an
end but all are relative to the end, e.g. the removing of fat, or
fat-removal, and the bodily parts themselves when one is making them
thin are in movement in this way (i.e. without being already that at
which the movement aims), this is not an action or at least not a
complete one (for it is not an end); but that movement in which the end
is present is an action. E.g. at the same time we are seeing and have
seen, are understanding and have understood, are thinking and have
thought (while it is not true that at the same time we are learning and
have learnt, or are being cured and have been cured). At the same time
we are living well and have lived well, and are happy and have been
happy. If not, the process would have had sometime to cease, as the
process of making thin ceases: but, as things are, it does not cease; we
are living and have lived.
Of these processes, then, we must call the one set movements, and the
other actualities. For every movement is incomplete-making thin,
learning, walking, building; these are movements, and incomplete at
that. For it is not true that at the same time a thing is walking and
has walked, or is building and has built, or is coming to be and has
come to be, or is being moved and has been moved, but what is being
moved is different from what has been moved, and what is moving from
what has moved. But it is the same thing that at the same time has seen
and is seeing, seeing, or is thinking and has thought.
The latter sort of process, then, I call an actuality, and the former a
movement.
7
What, and what kind of
thing, the actual is, may be taken as explained by these and similar
considerations. But we must distinguish when a thing exists potentially
and when it does not; for it is not at any and every time. E.g. is earth
potentially a man? No-but rather when it has already become seed, and
perhaps not even then. It is just as it is with being healed; not
everything can be healed by the medical art or by luck, but there is a
certain kind of thing which is capable of it, and only this is
potentially healthy. And (1) the delimiting mark of that which as a
result of thought comes to exist in complete reality from having existed
potentially is that if the agent has willed it it comes to pass if
nothing external hinders, while the condition on the other side-viz. in
that which is healed-is that nothing in it hinders the result. It is on
similar terms that we have what is potentially a house; if nothing in
the thing acted on-i.e. in the matter-prevents it from becoming a house,
and if there is nothing which must be added or taken away or changed,
this is potentially a house; and the same is true of all
other things the source of whose becoming is external. And (2) in the
cases in which the source of the becoming is in the very thing which
comes to be, a thing is potentially all those things which it will be of
itself if nothing external hinders it. E.g. the seed is not yet
potentially a man; for it must be deposited in something other than
itself and undergo a change.
But when through its own motive principle it has already got such and
such attributes, in this state it is already potentially a man; while in
the former state it needs another motive principle, just as earth is not
yet potentially a statue (for it must first change in order to become
brass.)
It seems that when we call a thing not something else
but 'thaten'-e.g. a casket is not 'wood' but 'wooden', and wood is not
'earth' but 'earthen', and again earth will illustrate our point if it
is similarly not something else but 'thaten'-that other thing is always
potentially (in the full sense of that word) the thing which comes after
it in this series. E.g. a casket is not 'earthen' nor 'earth', but
'wooden'; for this is potentially a casket and this is the matter of a
casket, wood in general of a casket in general, and this particular wood
of this particular casket. And if there is a first thing, which is no
longer, in reference to something else, called 'thaten', this is prime
matter; e.g. if earth is 'airy' and air is not 'fire' but 'fiery', fire
is prime matter, which is not a 'this'. For the subject or substratum is
differentiated by being a 'this' or not being one; i.e. the substratum
of modifications is, e.g. a man, i.e. a body and a soul, while the
modification is 'musical' or 'pale'. (The subject is called, when music
comes to be present in it, not 'music' but 'musical', and the man is not
'paleness' but 'pale', and not 'ambulation' or 'movement' but 'walking'
or 'moving',-which is akin to the 'thaten'.)
Wherever this is so, then, the ultimate subject is a substance; but when
this is not so but the predicate is a form and a 'this', the ultimate
subject is matter and material substance. And it is only right that 'thaten'
should be used with reference both to the matter and to the accidents;
for both are indeterminates.
We have stated, then, when a thing is to be said to
exist potentially and when it is not.
8
From our discussion of
the various senses of 'prior', it is clear that actuality is prior to
potency. And I mean by potency not only that definite kind which is said
to be a principle of change in another thing or in the thing itself
regarded as other, but in general every principle of movement or of
rest. For nature also is in the same genus as potency; for it is a
principle of movement-not, however, in something else but in the thing
itself qua itself. To all such potency, then, actuality is prior both in
formula and in substantiality; and in time it is prior in one sense, and
in another not.
(1) Clearly it is prior in formula; for that which is
in the primary sense potential is potential because it is possible for
it to become active; e.g. I mean by 'capable of building' that which can
build, and by 'capable of seeing' that which can see, and by 'visible'
that which can be seen. And the same account applies to all other cases,
so that the formula and the knowledge of the one must precede the
knowledge of the other.
(2) In time it is prior in this sense: the actual
which is identical in species though not in number with a potentially
existing thing is to it. I mean that to this particular man who now
exists actually and to the corn and to the seeing subject the matter and
the seed and that which is capable of seeing, which are potentially a
man and corn and seeing, but not yet actually so, are prior in time; but
prior in time to these are other actually existing things, from which
they were produced. For from the potentially existing the actually
existing is always produced by an actually existing thing, e.g. man from
man, musician by musician; there is always a first mover, and the mover
already exists actually. We have said in our account of substance that
everything that is produced is something produced from something and by
something, and that the same in species as it.
This is why it is thought impossible to be a builder
if one has built nothing or a harper if one has never played the harp;
for he who learns to play the harp learns to play it by playing it, and
all other learners do similarly. And thence arose the sophistical
quibble, that one who does not possess a science will be doing that
which is the object of the science; for he who is learning it does not
possess it. But since, of that which is coming to be, some part must
have come to be, and, of that which, in general, is changing, some part
must have changed (this is shown in the treatise on movement), he who is
learning must, it would seem, possess some part of the science.
But here too, then, it is clear that actuality is in this sense also,
viz. in order of generation and of time, prior to potency.
But (3) it is also prior in substantiality; firstly,
(a) because the things that are posterior in becoming are prior in form
and in
substantiality (e.g. man is prior to boy and human being to seed; for
the one already has its form, and the other has not), and because
everything that comes to be moves towards a principle, i.e. an end (for
that for the sake of which a thing is, is its principle, and the
becoming is for the sake of the end), and the actuality is the end, and
it is for the sake of this that the potency is acquired. For animals do
not see in order that they may have sight, but they have sight that they
may see. And similarly men have the art of building that they may build,
and theoretical science that they may theorize; but they do not theorize
that they may have theoretical science, except those who are learning by
practice; and these do not theorize except in a limited sense, or
because they have no need to theorize. Further, matter exists in a
potential state, just because it may come to its form; and when it
exists actually, then it is in its form. And the same holds good in all
cases, even those in which the end is a movement. And so, as teachers
think they have achieved their end when they have exhibited the pupil at
work, nature does likewise. For if this is not the case, we shall have
Pauson's Hermes over again, since it will be hard to say about the
knowledge, as about the figure in the picture, whether it is within or
without. For the action is the end, and the actuality is the action. And
so even the word 'actuality' is derived from 'action', and points to the
complete reality.
And while in some cases the exercise is the ultimate
thing (e.g. in sight the ultimate thing is seeing, and no other product
besides this results from sight), but from some things a product follows
(e.g. from the art of building there results a house as well as the act
of building), yet none the less the act is in the former case the end
and in the latter more of an end than the potency is.
For the act of building is realized in the thing that is being built,
and comes to be, and is, at the same time as the house.
Where, then, the result is something apart from the
exercise, the actuality is in the thing that is being made, e.g. the act
of building is in the thing that is being built and that of weaving in
the thing that is being woven, and similarly in all other cases, and in
general the movement is in the thing that is being moved; but where
there is no product apart from the actuality, the actuality is present
in the agents, e.g. the act of seeing is in the seeing subject and that
of theorizing in the theorizing subject and the life is in the soul (and
therefore well-being also; for it is a certain kind of life).
Obviously, therefore, the substance or form is
actuality.
According to this argument, then, it is obvious that actuality is prior
in substantial being to potency; and as we have said, one actuality
always precedes another in time right back to the actuality of the
eternal prime mover.
But (b) actuality is prior in a stricter sense also;
for eternal things are prior in substance to perishable things, and no
eternal thing exists potentially. The reason is this. Every potency is
at one and the same time a potency of the opposite; for, while that
which is not capable of being present in a subject cannot be present,
everything that is capable of being may possibly not be actual. That,
then, which is capable of being may either be or not be; the same thing,
then, is capable both of being and of not being. And that which is
capable of not being may possibly not be; and that which may possibly
not be is perishable, either in the full sense, or in the precise sense
in which it is said that it possibly may not be, i.e. in respect either
of place or of quantity or quality; 'in the full sense' means 'in
respect of substance'. Nothing, then, which is in the full
sense imperishable is in the full sense potentially existent (though
there is nothing to prevent its being so in some respect, e.g.
potentially of a certain quality or in a certain place); all
imperishable things, then, exist actually. Nor can anything which is of
necessity exist potentially; yet these things are primary; for if these
did not exist, nothing would exist. Nor does eternal movement, if there
be such, exist potentially; and, if there is an eternal mobile, it is
not in motion in virtue of a potentiality, except in respect of 'whence'
and 'whither' (there is nothing to prevent its having matter which makes
it capable of movement in various directions). And so the sun and the
stars and the whole heaven are ever active, and there is no fear that
they may sometime stand still, as the natural philosophers fear
they may. Nor do they tire in this activity; for movement is not for
them, as it is for perishable things, connected with the potentiality
for opposites, so that the continuity of the movement should be
laborious; for it is that kind of substance which is matter and potency,
not actuality, that causes this.
Imperishable things are imitated by those that are
involved in change, e.g. earth and fire. For these also are ever active;
for they have their movement of themselves and in themselves. But the
other potencies, according to our previous discussion, are all potencies
for opposites; for that which can move another in this way can also move
it not in this way, i.e. if it acts according to a rational formula; and
the same non-rational potencies will produce opposite results by their
presence or absence.
If, then, there are any entities or substances such
as the dialecticians say the Ideas are, there must be something much
more scientific than science-itself and something more mobile than
movement-itself; for these will be more of the nature of
actualities, while science-itself and movement-itself are potencies for
these.
Obviously, then, actuality is prior both to potency
and to every principle of change.
9
That the actuality is
also better and more valuable than the good potency is evident from the
following argument. Everything of which we say that it can do something,
is alike capable of contraries, e.g. that of which we say that it can be
well is the same as that which can be ill, and has both potencies at
once; for the same potency is a potency of health and illness, of rest
and motion, of building and throwing down, of being built and being
thrown down. The capacity for contraries, then, is present at the same
time; but contraries cannot be present at the same time, and the
actualities also cannot be present at the same time, e.g. health and
illness. Therefore, while the good must be one of them, the capacity is
both alike, or neither; the actuality, then, is better. Also in the case
of bad things the end or actuality must be worse than the potency; for
that which 'can' is both contraries alike. Clearly, then, the bad does
not exist apart from bad things; for the bad is in its nature posterior
to the potency. And therefore we may also say that in the things which
are from the beginning, i.e. in eternal things, there is nothing bad,
nothing defective, nothing perverted (for perversion is something bad).
It is an activity also that geometrical constructions
are discovered; for we find them by dividing. If the figures had been
already divided, the constructions would have been obvious; but as it is
they are present only potentially. Why are the angles of the triangle
equal to two right angles? Because the angles about one point are equal
to two right angles. If, then, the line parallel to the side had been
already drawn upwards, the reason would have been evident to any one as
soon as he saw the figure. Why is the angle in a semicircle in all cases
a right angle? If three lines are equal the two which form the base, and
the perpendicular from the centre -the conclusion is evident at a glance
to one who knows the former proposition. Obviously, therefore, the
potentially existing constructions are discovered by being brought to
actuality; the reason is that the geometer's thinking is an actuality;
so that the potency proceeds from an actuality; and therefore it is by
making constructions that people come to know them (though the single
actuality is later in generation than the corresponding potency).
10
The terms 'being' and
'non-being' are employed firstly with reference to the categories, and
secondly with reference to the
potency or actuality of these or their non-potency or non actuality, and
thirdly in the sense of true and false. This depends, on the side of the
objects, on their being combined or separated, so that he who thinks the
separated to be separated and the combined to be combined has the truth,
while he whose thought is in a state contrary to that of the objects is
in error. This being so, when is what is called truth or falsity
present, and when is it not? We must consider what we mean by these
terms. It is not because we think truly that you are pale, that you are
pale, but because you are pale we who say this have the truth. If, then,
some things are always combined and cannot be separated, and others are
always separated and cannot be combined, while others are capable either
of combination or of separation, 'being' is being combined and one, and
'not being' is being not combined but more than one. Regarding
contingent facts, then, the same opinion or the same statement comes to
be false and true, and it is possible for it to be at one time correct
and at another erroneous; but regarding things that cannot be otherwise
opinions are not at one time true and at another false, but the same
opinions are always true or always false.
But with regard to incomposites, what is being or not
being, and truth or falsity? A thing of this sort is not composite, so
as to 'be' when it is compounded, and not to 'be' if it is separated,
like 'that the wood is white' or 'that the diagonal is incommensurable';
nor will truth and falsity be still present in the same way as in the
previous cases. In fact, as truth is not the same in these cases, so
also being is not the same; but (a) truth or falsity is as
follows--contact and assertion are truth (assertion not being the same
as affirmation), and ignorance is non-contact. For it is not possible to
be in error regarding the question what a thing is, save in an
accidental sense; and the same holds good regarding non-composite
substances (for it is not possible to be in error about them). And they
all exist actually, not potentially; for otherwise they would have come
to be and ceased to be; but, as it is, being itself does not come to be
(nor cease to be); for if it had done so it would have had to come out
of something. About the things, then, which are essences and
actualities, it is not possible to be in error, but only to know them or
not to know them.
But we do inquire what they are, viz. whether they are of such and such
a nature or not.
(b) As regards the 'being' that answers to truth and
the 'non-being' that answers to falsity, in one case there is truth if
the
subject and the attribute are really combined, and falsity if they are
not combined; in the other case, if the object is existent it exists in
a particular way, and if it does not exist in this way does not exist at
all. And truth means knowing these objects, and falsity does not exist,
nor error, but only ignorance-and not an ignorance which is like
blindness; for blindness is akin to a total absence of the faculty of
thinking.
It is evident also that about unchangeable things
there can be no error in respect of time, if we assume them to be
unchangeable. E.g. if we suppose that the triangle does not
change, we shall not suppose that at one time its angles are equal to
two right angles while at another time they are not (for that would
imply change). It is possible, however, to suppose that one member of
such a class has a certain attribute and another has not; e.g. while we
may suppose that no even number is prime, we may suppose that some are
and some are not. But regarding a numerically single number not even
this
form of error is possible; for we cannot in this case suppose that one
instance has an attribute and another has not, but whether our judgement
be true or false, it is implied that the fact is eternal.
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