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Wrendolf C. Juntilla
Introduction
The
need to be conscientious of our beliefs is one of the most fundamental
exigencies of human life (Zagzebski 2009, p. 9). This is precisely so because
one cannot help but believe at least in something. We have to have beliefs in
order to make sense of our experiences and of our life in general. If these
beliefs were untrue we would have to entrust our lives in lies. Surely, this is
something which we do not want, for the conviction that our beliefs are true is
always corollary in the act of believing. Thus, if beliefs are fundamentally
connected to life, we must be able to trust that they are true. Anyone who is
lead to believe that there is nothing in this life worth believing is a
miserable person, indeed.
In an environment where trust in
reason was beginning to flourish, where the successes of the sciences were
shaping a new attitude of distrust to religious truths, and where people were
being caught between the old and the new system of beliefs and tradition, the
need to establish firm and true beliefs had been so demanding. One can simply
imagine the confusion it had brought and the temptation it had offered to
suspend beliefs either in reason or in faith. Skepticism in this environ was
lurking. This was the kind of atmosphere that Rene Descartes lived and felt (Sorell,
1987).
Conscientious and a Catholic
Christian as he is, Descartes, too, felt the demand to establish firm and true beliefs
(Descartes, 1980, p. 57, par. 17). But like many other intellectuals in his
time, he, too, is sandwiched between religion and science, neither of which he
wanted to give up. Thus, the challenged he posed upon himself was to address
skepticism by “establishing what is firm and lasting in the sciences” while remaining
consistent to the truths about faith and morals, particularly on the teachings
about God and the Soul. He believed that faith and reason are both indispensible
to be rejected. His letter to the theologians of Paris whom he dedicated his Meditations expressed his conviction to
give a defense on faith but by the use of natural reason. He wrote:
“I have always been of
the opinion that the two questions respecting God and the Soul were the chief
of those that ought to be determined by help of Philosophy rather than of
Theology; for although to us, the faithful, it be sufficient to hold as matters
of faith, that the human soul does not perish with the body, and that God
exists, it yet assuredly seems impossible ever to persuade infidels of the
reality of any religion, or almost even any moral virtue, unless, first of all,
those two things be proved to them by natural reason.” (1980, p. 45, par. 2)
This paper will present an
exposition of how Descartes had taken up these challenges in his Meditations particularly in Meditations 1, 2, 3, and 5, where he
entertained skepticism and endeavoured to solve it, built his anthropology, and
sought to prove God’s existence. After which, a critique will be provided: one
on his epistemology, the other on his proof of God’s existence, and the last on
his attempt to reconcile faith and reason, one which the I believe to be the
most explicit in his Meditations. Later,
I will try to support the claim that the necessity to prove God’s existence in
dealing with skepticism, as Descartes had noted, is more than an attempt to
make argumentation plausible; rather, it is an attempt to aid reason with faith
along with the recognition of our finitude and our need for the Absolute.
Meditation 1: Concerning Those Things That
Can Be Called into Doubt
Descartes realized that if he
were to save the sciences from the lurking of skepticism, he should entertain skepticism
himself (p. 57, par. 18). To do this he must withhold his assent to everything
he had once believed, even God and himself, until he could find that which is certain
and indubitable which shall become the foundation of the sciences. This would
have been difficult for him had he not proposed plausible sceptical arguments as
aides in his plunging into the dark state of doubting.
First, he proposes that it is
difficult to distinguish sleeping from being awake because the things that he
believed he experienced while he was awake were also the things that appeared
in his dream. This notion indicates already his long standing assumption that
experience is incoherent, uncertain, unreliable, and incapable of giving us
eternal truths. This is precisely his critique against empiricists who
champions the reliability of the sense experience (Sorell, 1987). Descartes
would suggest that our common sense view of the world is always subject to
error and falsity; hence, it is unreliable. He would later use this notion to
justify why it is important to view the world using the lenses of geometry and
mathematics. This is supported by the claim, following from his dream argument,
that whether in a waking life or in a dream certain qualities of things like extension,
number, and duration – qualities which are precisely the objects of geometry
and mathematics – remain immune from uncertainty (Descartes, 1980, p. 20, par.
28).
However,
this immunity is only to the extent that he has ideas of these clear and
distinct qualities. It still remains uncertain whether these qualities exist on
the things he perceives and whether things themselves exist. So, he pushes the
sceptical hypothesis a little further. It would be in a form of an Evil Genius
who is constantly deceiving him of everything. This time it would be pointless
to believe that qualities of things mentioned above which were deemed immune
from uncertainty can still retain their privilege status. It seems then that
with the presence of the Evil Genius, nothing whatsoever is certain.
Meditation 2: Concerning the Nature of the Human Mind: That
the Mind is More Known than the Body
After
having persuaded himself to doubt everything, even his own existence, he asked:
“Was I not, therefore, at the same time,
persuaded that I did not exist? Far from it; I assuredly existed, since I was
persuaded… Doubtless, then, I exist,
since I am deceived; and, let him deceive me as he may, he can never bring it
about that I am nothing, so long as I shall be conscious that I am some-thing”
(Descartes, 1980, p. 61, par. 25).
It
was under the seemingly inescapable sceptical argument about the Evil Genius
that Descartes has found also the seemingly inescapable truth about the self:
that it exists. This truth, however, is
not yet enough; he had to inquire about his own nature as an existent being.
He discovered that among those attributes
which he used to believe he has, including the body, there is one which really
does belong to him: thought – “this alone cannot be detached from me. I
am; I exist; this is certain”. “But for how long? For as long as I think” (p. 62,
par. 26). It was for this reason that Descartes was able to conclude that the
self is essentially a thinking self (p.
62, par. 27).
There
are two implications in this assertion. First, by claiming that the self is a
thinking self Descartes wants to point out the use of reason is innate in each
individual. This further advances his claim that geometrical truths are
accessible to everyone given the good habit and the proper use of the mind (Sorell,
1987). Second, by claiming that the thinking self is indubitable than the
corporeal things truth would then have to be found in this indubitable center.
We can see this implicitly in his Wax Argument. In this argument, Descartes
claimed that what he perceived about the wax was never the physical appearance
for even after it changed he still conceived of the same wax. Thus, he
concluded that the comprehension he has of the wax was in no way imagined or
sensed, but “perceived by the mind only”. This would construe Descartes claim
that knowledge is not knowledge of things but knowledge of our ideas of things (Luijpen,
1960, p. 79). Inevitably, he is lead to conclude that experience, which
contemporary philosophers call an event in which encounter the world, is not
necessary in attaining truth.
Following this assertion of the certainty of
the thinking self, it would not be a surprise then to see why Descartes has
claimed that the mind is better and certainly known than corporeal things. This
is because it could happen that what he believed he perceived such as the wax
can be mistaken, but it could not happen that “while [he] sees, or think [he]
sees, [he] who thinks is not something” (Descartes, 1980, p. 66, par. 33).
Even then, Descartes would want to know if we
can have true knowledge of things outside our minds. He would loathe imagining
that the thinking self is nothing but a vacuum, a locked, lone cell. To avoid
this horror he would have to get out of himself; so he tried to seek God.
Meditation 3:
Concerning God, That He Exists
Informed
by the assumption that sense-perception is incoherent, Descartes has already
assessed a priori that we cannot acquire clear and distinct ideas coming from
experience. If he wants to be successful in winning his battle against
skepticism, he has to prove that there are indeed clear and distinct ideas. He
believes he is successful on this matter with regards to the self, thus giving
a philosophical foundation on the belief of the immortality of the soul. Owing
to this success, Descartes realizes that attributing truth to clear and
distinct ideas would earn him more success especially in his investigation
about God and the world. Thus, he gives this as a general rule: “what I clearly
and distinctly perceive is true” (p. 67,
par. 35).
Economizing on these clear and
distinct ideas, Descartes, then, had to inquire what ideas he has in him which
can be considered clear and distinct. In Meditation
1, he has already affirmed that mathematical and geometrical truths are
clear and distinct. Nevertheless, believing that he has these clear and
distinct ideas is not enough a proof that indeed, these ideas are clear and
distinct, since this can no longer be maintained once the idea of an Evil
Genius is entertained. There is no other way to tell that what he believes to
be clear and distinct is really clear and distinct than to inquire whether or
not some God could have given him a nature such that he might be deceived. Thus,
he said, “…in order to remove this doubt, I ought at the first opportunity to
inquire if there is a God, and, if there is, whether or not he can be a
deceiver. If I am ignorant of these matters, I do not think I can ever be
certain of anything else” (p. 68, par. 36).
Guided by his general rule, to
prove God’s existence requires him to prove that the idea he has of God is
clear and distinct, hence true. This method will later lead him to a vicious
circle, for the existence of clear and distinct ideas is not proven unless
God’s existence is proven first, but God’s existence cannot be proven unless
there is a clear and distinct idea of him.
In order to know if there is a
clear and distinct idea of God, Descartes has to classify the types of ideas
there are. He noted that there can be three types: innate, adventitious, and
fictitious. Innate ideas refer to those which are acquired a priori. Descartes
believe that the ideas about the self and geometrical and mathematical truths
belong to this type. Adventitious ideas are ideas which refer to the reality
outside our mind such as “chair”, “table”, “computer”, etc. These ideas are
believed to have been acquired from sense-experience. Later, Descartes would
challenge this belief. The last type of ideas is fictitious. They are ideas
which are only products of imagination. Examples of these are “elf”, “centaurs”,
“superman”, etc.
Since it is immediately evident
that things do not come into being without causes, it follows that it is
impossible for an idea to be conceived in the mind unless there is a cause of
this idea, and this cause must contain everything that can be found in an idea.
Although this cause does not transmit its mind-independent reality into the
mind, it does not mean that the idea derived from this cause is not real. This
is because the very nature of ideas is that they are not mind-independent
unlike their causes. Nevertheless, the essence or whatness of ideas is derived
from the things that caused them. However, it does not follow that this essence
exists in the thing independent of the mind. Rather, this essence exists
insofar as the thing is conceived by the mind (p. 72, par. 42).
From this point, Descartes gains
justification to his notion that ideas may not necessarily conform to things as
they are in themselves. According to him, we seem to be taught by nature or
that we naturally believe that ideas about objects outside our minds are
similar to these objects. However, Descartes believes that this is unwarranted.
First of all, he notes that our common-sense view of the world can be mistaken.
For example, the pre-scientific conception of the sun is that it is very small
when in fact it is several times larger than the earth. Second, even if we
recognize that having these ideas does not depend on our actually willing it, on
our choosing to create these ideas, still it does not follow that these ideas
come from the objects themselves. This is because there might be some other
faculty in us other than our will which produces these ideas. He makes the
point that even during sleep, when we do not will at all, we are able to
acquire this type of ideas. Therefore,
for Descartes, “all of this demonstrates sufficiently that up to this point
[we] have believed not by certain judgment, but only by a blind impulse that
things exist outside [us] that send their ideas or images into [us] through the
sense organs or by some other means” (p. 70, par. 39).
This is to indicate that, for
Descartes, ideas which refer to objects outside of us, which are believed to
have been acquired through sense-experience, is not clear and distinct. This is
a spit on the face to the old traditional empiricist maxim that “To see is to
believe”. Clearly, it suggests that God’s existence cannot be proved through
sense-experience. Thus, if the idea of God is to be clear and distinct, it
would have to be innate. By innate, Descartes does not mean that this idea is
caused by us. Rather, he means that this idea is acquired a priori, without the
participation of sense-experience. Needless to say, Descartes assumes that the
idea of God has a different status than the ideas of objects (pp. 72-74).
He vivifies this notion by
claiming that when ideas are only considered as mere modes of thinking, there
is no point of believing that they are of different status. However, when it
comes to the content of these ideas, it is clear that some ideas exhibit more
objective reality than others. When Descartes speak of objective reality, he
means the perfection that an idea presents to the consciousness. Thus, ideas of
finite realities has less objective content than those that exhibit infinite
realities like geometrical and material truths and idea of God, who is
“eternal, infinite, omniscient, omnipotent, and creator of all things.”
Descartes would later advance the claim that the idea of God is the most clear
and distinct because it exhibits the most objective reality (p. 75, par. 47).
Since he has this idea of something
with an uttermost perfection, it would then be necessary to inquire whether he
can or cannot be the cause of this idea. Establishing the principles that the
cause cannot be greater than its effect, that something cannot come from
nothing, and that the more perfect cannot come from the less perfect, Descartes
concluded there is no other cause of this idea of God than God himself: “the
idea of God is something that cannot be generated from me. The idea of an
infinite substance cannot proceed from me who is finite. Thus, God necessarily
exists [as the cause of this idea]” (p. 74).
How
does this show that the idea of God is innate? The answer is lucid: given this
line of thinking, it follows that “the perception of God exists prior to the
perception of myself…Why would I know that I doubt and I desire, that is, that
I lack something and that I am not wholly perfect, if there were no idea in me
of a more perfect being by comparison with which I might acknowledge my
defects?” (p.74, par. 46) So, the idea of self as finite depends on the idea of
God as infinite; and if the idea of self is immediately perceived, so much so
is the idea of God.
Consequently,
Descartes gives us one of his most important assertions: “It is the idea [of
God] that is clear and distinct in the highest degree; for whatever I clearly
and distinctly perceive that is real and true and that contains some perfection
is wholly contained in that idea” (p. 74). Later, he will make this his presupposition
in his grounding of the sciences to God.
While Descartes was already
convinced that God exists, nonetheless he still wanted to entertain some doubts
regarding this assertion. One of those was the possibility that perhaps what he
attributes to God is really in him potentially. Later, however, he realized
that he had to dismiss such a possibility from the fact that no matter how he
conceives it, the self is always finite. This recognition of the finitude of
the self enabled Descartes to affirm also that even the self comes from God. He
made it as a point that if he, who cannot account for his own existence,
depends upon a cause other than himself in order to exist, and that if he
possesses an idea of infinite perfection, it follows that the cause of his
existence must be of an infinite perfection also (again, presupposing the
principle that no effect is greater than its cause). This is precisely the
attribute of God; hence, goes his proof of God’s existence, a second time.
Descartes’ conclusion from these
arguments is overwhelming:
“The whole force of the argument rests on the fact that I
recognize that it is impossible that I should exist, having the idea of God in
me, unless God in fact does exist. God, I say, that same being whose idea is in
me: a being having all those perfections that I cannot comprehend, but in some
way can touch with my thought, and a being subject to no defects. From these
things it is sufficiently obvious that he cannot be a deceiver. For it is manifest by the light of nature that fraud and
deception depends on some defect.” (p. 78, par. 52)
Thus,
Descartes, judging from his own angle, has solved the sceptical problems about
the self and about God. What remains now is to overcome skepticism about the
material world.
Meditation 5:
Concerning the Essence of Material Things, and Again Concerning God, That He
Exists
Descartes begins this meditation
by expressing his desire to free himself from the doubts into which he has
recently fallen concerning material things. Granted that he can now trust his
faculty of judgment because he was able to prove that his nature comes from an
infinitely perfect and absolutely good Creator who is a non-deceiver, so he is
now confident that whatever he judges about material things can be relied upon
provided the same tact and prudence he has been practicing in his past
meditations.
To see whether there is certaint
about material things or not, he must first consider whether or not there can
be clear and distinct ideas of material things. But there, indeed, are distinct
ideas about material things: these are extension, number, and duration. He
gives an example of a triangle: whether a triangle really exists or not, or
whether I want it or not, is irrelevant to the fact that its three angles is
equal to two right angles, that its longest side is opposite the largest angle,
and so on. An idea like this and of other figures and numbers do not come from
sense-experience; they are acquired a priori, “since [we] can think of many
other figures (for example, a chiliagon) without these things having entered me
through the senses”. “[He] always took this type of truth to be the most
certain of every truth that [he] evidently knew regarding figures, numbers, or
other things pertaining to arithmetic, geometry or, in general, to pure and
abstract mathematics” (p. 85).
Following from this, Descartes
wants to advance a proof of God’s existence once again. Having noted that even
in material things we can have clear and distinct ideas so it cannot be denied
that the idea of a supremely perfect being is no less than the idea of some
figure or number.
It
pertains to God’s nature that he always exists. This is because, being
infinitely perfect, it is repugnant to think of God as lacking existence. It
follows that existence is inseparable from God; for this reason he truly exists.
Finally, he was able to reach into
his ultimate conclusion:
“…once
I perceived that there is a God – because at the same time I also understood
that all other things depend on him – and that he is no deceiver, I then
concluded that everything that I clearly and distinctly perceive is necessarily
true…And thus I plainly see that the certainty and truth of every science
depends upon the knowledge of the true God…” (pp. 88-89)
Since truth of every science
depends upon clear and distinct ideas, and since clear and distinct ideas
depend upon God who is the source of everything, so the truth of every science
depends upon God. It is in God that Descartes believed himself to have found what
is lasting and firm in the sciences.
Between Faith and Reason: The Cartesian
Experience
What
is interesting in Descartes’ Meditations is
his attempt to reconcile science and religion. This agenda is probably not
something new among many contemporary thinkers, but considering Descartes own
period, surely such approach is a breakthrough in the history of philosophy.
Many
of Descartes’ critics would reject his concept of the human person, his theory
of knowledge, and his proof of God’s existence. Nevertheless, it is unwarranted
to claim that Descartes’ attempt to solve the problems of skepticism has been
unsuccessful. In the following paragraphs we shall present briefly the naiveté
of some of Descartes’ arguments, and show why, despite these, his approach to
scepticism is still not invalid.
First
of Descartes’ naïve assertions is his affirmation that ideas of material things
are caused by material things themselves but that these ideas are not
reflective of things as they are in themselves. For example, Descartes would
affirm that the idea I have of a chair is caused or co-caused by the chair in
reality, but we do not have the grounds to conclude that this idea of a chair
is what really the chair is in reality independent of my mind. Existentialist
metaphysicians would claim that this belief is a contradiction (for comparison,
see Clarke 2001). If we are to faithfully follow Descartes line of thought, we
can reach a conclusion different from where is led. This is because Descartes
himself attributes more reality to a cause than to the effect, the very
principle he used in proving God’s existence. If an effect (idea) refers to an
existent substance, surely its cause must also be an existent substance. If an
idea tells us those attributes of this existent substance, surely its cause,
the existent substance, must also posses those attributes. Affirming this truth
would entail that what things present to the mind through sense-perception is
true. This is simply unacceptable for him, for it has been his bias that truth
must be fixed, eternal, and a priori.
The
other naïve assertion of Descartes is concerning his proof of God’s existence.
Apparently, it assumes the same form with that of St. Anselm. It consists in
asserting that God, as we know him, cannot not exist, for he is the most
perfect of all beings. Since non-existence is non-perfection, it cannot happen that
we apprehend the idea of God but deny that he exists. In fact, if God is to be
a God, he must be a self-existent being. Although this supports the conclusion
that God must necessarily exist, still
it does not support the conclusion that God actually
exists. Logicians such as Bacchuber (1957) had noted that the proposition
“God is a self-existent being” does not have a real supposition. This means
that the “God” being meant in that assertion is not the God who is in reality,
but the God as conceived by the mind. In other words, it is not God that is
being referred to, but the concept of
God that is supposed. Descartes would have agreed on this if he had been more
prudent, for he himself had affirmed that no cause is greater than its effect.
Thus, the idea (effect) that God is a necessary being cannot make God (cause)
exists. Logicians call St. Anselm’s, and now Descartes’ error, existential fallacy (Bacchuber, 1957, p.
234).
Despite
these naivetes, Descartes can still be said to have overcome scepticism, at
least from my own point of view. One of the things that skepticism destroys is
the belief we have of ourselves, the confidence and self-trust that what we
believe to be true are indeed true. Although this is not explicit to Descartes
himself, his attempt to regain self-trust after putting himself into the world
of scepticism, of making himself a willing victim in the dark world of
uncertainties, and his self-evident belief of his victory, of regaining self-trust
in the end, is in fact one of the most fundamental requirements in overcoming
scepticism – that is – to become not sceptic anymore.
However,
this is not to say that one can easily overcome scepticism by just dismissing
or not taking it seriously. Skepticism threatens self-trust, and self-trust can
only be regained if one is conscientious of his beliefs. Being conscientious
entails that one does not dismiss the threat of scepticism carelessly. So if
one is to be authentic, he cannot simply dismiss scepticism.
In
Descartes’ situation, scepticism lurks on the tension between faith and reason.
On one hand, there are those who distrust the capacity of reason to attain
truth. On the other hand, there are those who deny the relevance of faith in the
search for knowledge. Here we understand why Descartes had so much wanted to
destroy this tension, thus destroy scepticism. If we try to go back into
Descartes’ basic arguments, we would have something like this:
a.
I have to find certainty.
b.
I can be certain if I can trust myself to have a
nature that can reach certainty.
c.
I can prove that I have a nature that can reach
certainty if I can prove that God, who is thought to be the source of all
things even of myself, exists and that he did not give me a nature that can be
deceived.
d.
I can prove that God exists if the idea I have
of him is clear and distinct (for whatever is clear and distinct is true).
e.
The idea of God who is infinitely perfect and
absolutely good, one who cannot not exist, is the most clear and distinct of
all ideas.
f.
Therefore, God exists.
g. Therefore, I can trust myself for I came from
God, who, being so infinitely perfect and absolutely good, cannot deceive me or
give a nature that is subject to deception.
Here
we find a familiar anxiety of the need to be able to trust our faculty of
reasoning in our search for knowledge. This necessity impels Descartes to prove
that God exists, for it is in such proof that we can assure ourselves that we
have a nature that can attain truth and certainty. But what is interesting is
that, Descartes is demonstrating God’s
existence using the very faculty which he himself is putting into question.
Thus, he already put trust on himself and on his own faculty even before he begins
demonstrating God’s existence. Apparently, this pre-philosophical act of
self-trust is a leap of faith, since he did not ground this into something
which he has already demonstrated. However, this faith cannot be said to be
groundless nor does it make the self its own ground. Rather, it is a faith on
someone other than oneself. This is so because it would be pointless for
Descartes to rely on God for the possibility of truth and so the need to seek
his existence unless Descartes himself recognizes that the trust that he is
putting on himself is only to the extent that he believes and trusts that God, who is his creator, is no deceiver.
This is why he believes he can make himself his point of departure in finding
God: by reflecting upon himself and upon his ideas to prove God’s existence he
expresses the faith that God is for him, not against him.
So,
there goes the question, “Is it necessary for Descartes to put God as the
foundation of knowledge?” This is difficult to answer. First of all, if
Descartes had been an atheist he could have made a different argument. So it
would appear that the “God-foundation” is only his religious bias. Second of
all, even if he is not an atheist himself, he can still formulate an argument
that does not lead to the “God-foundation”, for the belief that God is no
deceiver may not be relevant as proof of certainty. Nevertheless, if we are to read
Descartes’ Meditations from a
perspective of an author who, in the midst of scepticism, recognizes his own
finitude and his need for the Absolute as his basis of self-trust, then we can
say the proving God’s existence and putting him as the foundation of all
knowledge is as necessary as overcoming scepticism. This supports the reason
why he tried to knit faith and reason together.
Descartes
himself would not deny that what saved him from scepticism and gained for him
certainty is not the fact that he was able to establish clear and distinct
ideas, but from the fact that he was able to trust that that these clear and
distinct ideas are true for they have God, who is not a deceiver, as their
source. But the point is, this confidence is not really grounded on his assent
to arguments, for Descartes himself affirmed that the even the truth of his
arguments depend on this confidence (Descartes, 1980, p. 68). Hence, we have a
valid reason to infer that grounding God as the foundation of the sciences is
more than a discourse of Descartes in order to address sceptical problems. It
is rather a paradoxical expression of certainty in the midst of uncertainty,
that is – of being certain that God would not deceive us while at same time
being uncertain of our capacity to reach truth on our own unless we have God as
our foundation.
At
the end of the day, I believe that what Descartes has acquired that granted him
to found the sciences of his days is not a concept but a disposition, a certain confidence that by virtue of his being a
creature of an infinitely perfect and good God, then he has in him a faculty
that shall not bring him into error and deception.
Reading
the Meditations, then, can be like
reading a tale of a spiritual journey of a soul longing for the Absolute;
indeed, a typical Cartesian experience.
Cited Materials:
Bacchuber,
Andrew. Introduction to Logic. (New York: Appleton-Century Croft, Inc., 1957).
Clarke,
Norris W. The One and the Many: A Contemporary Thomistic Metaphysics. (Indiana :
University of Notre Dame Press, 2001).
Descartes,
Rene. Discourse on Method and Meditations
on First Philosophy. Translated by Donald A. Cress. (USA: Hackett
Publishing Company, 1980).
Luijpen, William A. Existential Phenomenology,.
(USA: Duquesne University Press, 1960), 79-84.
Sorell, Tom. Descartes. Past Masters series.
(USA: Oxford Universty Press, 1987).
Zagzebski, Linda. On Epistemology.
(USA: Wadsworth, Cengage Learning. 2009).
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