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Theaetetus, knowledge is a subset of that which is
both true and believed
Greek ep?st?µ? - episteme, "knowledge" + ?????,
or theory of knowledge is a branch of
philosophy concerned with the nature and scope of
The term was introduced into English by the Scottish philosopher
James Frederick Ferrier (1808-1864).
Much of the debate in this field has focused on
analyzing the nature of knowledge and how it relates to similar
notions such as
justification. It also deals with the means of production of
knowledge, as well as skepticism about different knowledge claims.
In other words, epistemology primarily addresses the following
questions: "What is knowledge?", "How is knowledge acquired?", and
"What do people know?"
The primary question that epistemology addresses is
knowledge?" This question is several millennia old.
Distinguishing knowing that from
In this article, and in epistemology in general, the kind of
knowledge usually discussed is
propositional knowledge, also known as "knowledge-that" as
opposed to "knowledge-how." For example: in mathematics, it is known
that 2 + 2 = 4, but there is also knowing how to add
two numbers. Many (but not all) philosophers thus think there is an
important distinction between "knowing that" and "knowing how", with
epistemology primarily interested in the former. This distinction is
recognized linguistically in many languages, though not in modern
English except as dialect (see verbs "ken" and "wit" in the Shorter
In Personal Knowledge,
Michael Polanyi articulates a case for the epistemological
relevance of both forms of knowledge; using the example of the act
of balance involved in riding a
bicycle, he suggests that the theoretical knowledge of the
physics involved in maintaining a state of
balance cannot substitute for the practical knowledge of how to
ride, and that it is important to understand how both are
established and grounded. It is worth pointing out that in recent
times, some epistemologists (see Sosa, Greco, Kvanvig, Zagzebski)
have argued that we should not think of knowledge this way;
Epistemology should evaluate people's properties (i.e.,intellectual
virtues) instead of propositions' properties. This is, in short,
because higher forms of cognitive success (i.e., understanding)
involve non 'veritic' features which can't be evaluated from a
justified true belief view of knowledge.
Often, statements of "belief" mean that the speaker predicts
something that will prove to be useful or successful in some sense —
perhaps the speaker might "believe in" his or her favorite football
team. This is not the kind of belief usually addressed within
epistemology. The kind that is dealt with is when "to believe
something" simply means any cognitive content held as true. For
example, to believe that the sky is blue is to think that the
proposition, "The sky is blue," is true.
Knowledge implies belief. The statement "I know P, but I
don't believe that P is true" is contradictory. To know P
is, among other things, to believe that P is true, or to
believe in P. (See the article on
Moore's paradox.) Knowing That and Knowing How are
just two aspects of knowledge proper.
- See also:
Criteria of truth
If someone believes something, he or she thinks that it is true
but may be mistaken. This is not the case with knowledge. For
example, a man thinks that a particular bridge is safe enough to
support him, and he attempts to cross it; unfortunately, the bridge
collapses under his weight. It could be said that the man
believed that the bridge was safe, but that his belief was
mistaken. It would not be accurate to say that he knew
that the bridge was safe, because plainly it was not. By contrast,
if the bridge actually supported his weight then he might be
justified in subsequently holding that he knew the bridge had
been safe enough for his passage, at least at that particular time.
For something to count as knowledge, it must actually be true.
The Aristotelian definition of truth states:
To say of something which is that it is not, or to say of
something which is not that it is, is false. However, to say of
something which is that it is, or of something which is not that it
is not, is true."
considers a number of theories as to what knowledge is, the last being that
knowledge is true belief that has been "given an account of" — meaning explained
or defined in some way. According to the theory that knowledge is justified true
belief, in order to know that a given proposition is true, one must not only
believe the relevant true proposition, but one must also have a good reason for
doing so. One implication of this would be that no one would gain knowledge just
by believing something that happened to be true. For example, an ill person with
no medical training, but a generally optimistic attitude, might believe that
he/she will recover from his/her illness quickly. Nevertheless, even if this
belief turned out to be true, the patient would not have known that
he/she would get well since his/her belief lacked justification. The definition
of knowledge as justified true belief was widely accepted until the 1960s. At
this time, a paper written by the American philosopher
Edmund Gettier provoked widespread discussion. See
theories of justification for other views on the idea.
The Gettier problem
Edmund Gettier called into question the theory of knowledge that had been
dominant among philosophers for thousands of years.
In a few pages, Gettier argued that there are situations in which one's belief
may be justified and true, yet fail to count as knowledge. That is, Gettier
contended that while justified belief in a proposition is necessary for that
proposition to be known, it is not sufficient. As in the diagram above, a true
proposition can be believed by an individual but still not fall within the
"knowledge" category (purple region).
According to Gettier, there are certain circumstances in which one does not
have knowledge, even when all of the above conditions are met. Gettier proposed
thought experiments, which have come to be known as "Gettier cases", as
counterexamples to the classical account of knowledge. One of the cases
involves two men, Smith and Jones, who are awaiting the results of their
applications for the same job. Each man has ten coins in his pocket. Smith has
excellent reasons to believe that Jones will get the job and, furthermore, knows
that Jones has ten coins in his pocket (he recently counted them). From this
Smith infers, "the man who will get the job has ten coins in his pocket."
However, Smith is unaware that he has ten coins in his own pocket. Furthermore,
Smith, not Jones, is going to get the job. While Smith has strong evidence to
believe that Jones will get the job, he is wrong. Smith has a justified true
belief that a man with ten coins in his pocket will get the job; however,
according to Gettier, Smith does not know that a man with ten coins in
his pocket will get the job, because Smith's belief is "...true by virtue of the
number of coins in Smith's pocket, while Smith does not know how many
coins are in Smith's pocket, and bases his belief...on a count of the coins in
Jones's pocket, whom he falsely believes to be the man who will get the job."
 p.122.) These cases fail
to be knowledge because the subject's belief is justified, but only happens to
be true in virtue of luck.
Responses to Gettier
The responses to Gettier have been varied. Usually, they have involved
substantive attempts to provide a definition of knowledge different from the
classical one, either by recasting knowledge as justified true belief with some
additional fourth condition, or as something else altogether.
In one response to Gettier, the American philosopher
Richard Kirkham has argued that the only definition of knowledge that could
ever be immune to all counterexamples is the
infallibilist one. To qualify as an item of knowledge, so the theory
goes, a belief must not only be true and justified, the justification of the
belief must necessitate its truth. In other words, the justification for
the belief must be infallible. (See
Fallibilism, below, for more information.)
Yet another possible candidate for the fourth condition of knowledge is
indefeasibility. Defeasibility theory maintains that there should be no
overriding or defeating truths for the reasons that justify one's belief. For
example, suppose that person S believes they saw Tom Grabit steal a book
from the library and uses this to justify the claim that Tom Grabit stole a book
from the library. A possible defeater or overriding proposition for such a claim
could be a true proposition like, "Tom Grabit's identical twin Sam is currently
in the same town as Tom." So long as no defeaters of one's justification exist,
a subject would be epistemically justified.
The Indian philosopher
B K Matilal has drawn on the
fallibilism tradition to respond to the Gettier problem. Nyaya theory
distinguishes between know p and know that one knows p - these are
different events, with different causal conditions. The second level is a sort
of implicit inference that usually follows immediately the episode of knowing p
(knowledge simpliciter). The Gettier case is analyzed by referring to a
Gangesha (13th c.), who takes any true belief to be knowledge; thus a true
belief acquired through a wrong route may just be regarded as knowledge
simpliciter on this view. The question of justification arises only at the
second level, when one considers the knowledgehood of the acquired belief.
Initially, there is lack of uncertainty, so it becomes a true belief. But at the
very next moment, when the hearer is about to embark upon the venture of knowing
whether he knows p, doubts may arise. "If, in some Gettier-like cases, I
am wrong in my inference about the knowledgehood of the given occurrent belief
(for the evidence may be pseudo-evidence), then I am mistaken about the truth of
my belief -- and this is in accord with Nyaya fallibilism: not all
knowledge-claims can be sustained."
Reliabilism is a theory advanced by philosophers such as
Goldman according to which a belief is justified (or otherwise supported in
such a way as to count towards knowledge) only if it is produced by processes
that typically yield a sufficiently high ratio of true to false beliefs. In
other words, this theory states that a true belief counts as knowledge only if
it is produced by a reliable belief-forming process.
Reliabilism has been challenged by Gettier cases. Another argument that
challenges reliabilism, like the Gettier cases (although it was not presented in
the same short article as the Gettier cases), is the case of Henry and the barn
façades. In the thought experiment, a man, Henry, is driving along and sees a
number of buildings that resemble barns. Based on his perception of one of
these, he concludes that he has just seen barns. While he has seen one, and the
perception he based his belief on was of a real barn, all the other
he saw were façades. Theoretically, Henry doesn't know that he has seen a barn,
despite both his belief that he has seen one being true and his belief being
formed on the basis of a reliable process (i.e. his vision), since he only
acquired his true belief by accident.
The American philosopher
Robert Nozick has offered the following definition of knowledge:
S knows that P if and only if:
- S believes that P;
- if P were false, S would not believe that P;
- if P is true, S will believe that P.
Nozick believed that the third subjunctive condition served to address cases
of the sort described by Gettier. Nozick further claims this condition addresses
a case of the sort described by
D. M. Armstrong:
A father believes his son innocent of committing a particular crime, both
because of faith in his son and (now) because he has seen presented in the
courtroom a conclusive demonstration of his son's innocence. His belief via the
method of the courtroom satisfies the four subjunctive conditions, but his
faith-based belief does not. If his son were guilty, he would still believe him
innocent, on the basis of faith in his son; this would violate the third
The British philosopher
Simon Blackburn has criticized this formulation by suggesting that we do not
want to accept as knowledge beliefs which, while they "track the truth" (as
Nozick's account requires), are not held for appropriate reasons. He says that
"we do not want to award the title of knowing something to someone who is only
meeting the conditions through a defect, flaw, or failure, compared with someone
else who is not meeting the conditions."
Timothy Williamson, has advanced a theory of knowledge according to which
knowledge is not justified true belief plus some extra condition(s). In his book
Knowledge and its Limits, Williamson argues that the concept of
knowledge cannot be analyzed into a set of other concepts—instead, it is
generis. Thus, though knowledge requires justification, truth, and
belief, the word "knowledge" can't be, according to Williamson's theory,
accurately regarded as simply shorthand for "justified true belief".
Externalism and internalism
Part of the debate over the nature of knowledge is a debate between
epistemological externalists on the one hand, and epistemological internalists
on the other. Externalists think that factors deemed "external", meaning outside
of the psychological states of those who gain knowledge, can be conditions of
knowledge. For example, an externalist response to the Gettier problem is to say
that, in order for a justified, true belief to count as knowledge, it must be
caused, in the right sort of way, by relevant facts. Such causation, to the
extent that it is "outside" the mind, would count as an external,
knowledge-yielding condition. Internalists, contrariwise, claim that all
knowledge-yielding conditions are within the psychological states of those who
René Descartes, prominent philosopher and supporter of internalism wrote
that, since the only method by which we perceive the external world is through
our senses, and that, since the senses are not infallible, we should not
consider our concept of knowledge to be infallible. The only way to find
anything that could be described as "infallibly true," he advocates, would be to
pretend that an omnipotent, deceitful being is tampering with one's perception
of the universe, and that the logical thing to do is to question anything that
involves the senses. "Cogito ergo sum" (I think, therefore I am) is commonly
associated with Descartes' theory, because he postulated that the only thing
that he could not logically bring himself to doubt is his own existence: "I do
not exist" is a contradiction in terms; the act of saying that one does not
exist assumes that someone must be making the statement in the first place.
Though Descartes could doubt his senses, his body and the world around him, he
could not deny his own existence, because he was able to doubt and must exist in
order to do so. Even if some "evil genius" were to be deceiving him, he would
have to exist in order to be deceived. However from this Descartes did not go as
far as to define what he was. This was pointed out by the materialist
philosopher Pierre Gassendi (1592-1655) who accused Descartes of saying that he
was "not this and not that," while never saying what exactly was existing. One
could argue that this is not an edifying question, because it doesn't matter
what exactly exists, it only matters that it does indeed exist.
The second question that will be dealt with is the question of how knowledge
is acquired. This area of epistemology covers what is called "the regress
problem", issues concerning epistemic distinctions such as that between
apriority as means of creating knowledge. Further that between synthesis and
analysis used as a means of proof, and debates such as the one between
empiricists and rationalists.
The regress problem
Suppose we make a point of asking for a justification for every belief. Any
given justification will itself depend on another belief for its justification,
so one can also reasonably ask for this to be justified, and so forth. This
appears to lead to an infinite regress, with each belief justified by some
further belief. The apparent impossibility of completing an infinite chain of
reasoning is thought by some to support
The skeptic will argue that since no one can complete such a chain, ultimately
no beliefs are justified and, therefore, no one knows anything. "The only thing
I know for sure is that I do not know for sure."
Response to the regress problem
Many epistemologists studying justification have attempted to argue for
various types of chains of reasoning that can escape the regress problem.
Some philosophers, notably
Klein in his "Human Knowledge and the Infinite Regress of Reasons",
have argued that it's not impossible for an infinite justificatory series to
exist. This position is known as "infinitism".
Infinitists typically take the infinite series to be merely potential, in the
sense that an individual may have indefinitely many reasons available to him,
without having consciously thought through all of these reasons. The individual
need only have the ability to bring forth the relevant reasons when the need
arises. This position is motivated in part by the desire to avoid what is seen
as the arbitrariness and circularity of its chief competitors, foundationalism
Foundationalists respond to the regress problem by claiming that some
beliefs that support other beliefs do not themselves require justification by
other beliefs. Sometimes, these beliefs, labeled "foundational", are
characterized as beliefs that one is directly aware of the truth of, or as
beliefs that are self-justifying, or as beliefs that are infallible. According
to one particularly permissive form of foundationalism, a belief may count as
foundational, in the sense that it may be presumed true until defeating evidence
appears, as long as the belief seems to its believer to be true. Others have argued that a belief is justified if it
is based on perception or certain a priori considerations.
Criticism of Foundationalism
The chief criticism of foundationalism is that it allegedly leads to the
arbitrary or unjustified acceptance of certain beliefs.
Another response to the regress problem is
coherentism, which is the rejection of the assumption that the regress
proceeds according to a pattern of linear justification. To avoid the charge of
coherentists hold that an individual belief is justified circularly by the
way it fits together (coheres) with the rest of the belief system of which it is
a part. This theory has the advantage of avoiding the infinite regress without
claiming special, possibly arbitrary status for some particular class of
beliefs. Yet, since a system can be coherent while also being wrong,
coherentists face the difficulty in ensuring that the whole system
corresponds to reality.
There is also a position known as "foundherentism".
Haack is the philosopher who conceived it, and it is meant to be a
unification of foundationalism and coherentism. One component of this theory is
what is called the "analogy of the crossword puzzle". Whereas, say, infinists
regard the regress of reasons as "shaped" like a single line, Susan Haack has
argued that it is more like a crossword puzzle, with multiple lines mutually
supporting each other.
A priori and a posteriori knowledge
The nature of this distinction has been disputed by various philosophers;
however, the terms may be roughly defined as follows:
- A priori knowledge is knowledge that is known independently of
experience (that is, it is non-empirical).
- A posteriori knowledge is knowledge that is known by experience
(that is, it is empirical).
Some propositions are such that we appear to be justified in believing them
just so far as we understand their meaning. For example, consider, "My father's
brother is my uncle." We seem to be justified in believing it to be true by
virtue of our knowledge of what its terms mean. Philosophers call such
propositions "analytic". Synthetic propositions, on the other hand, have
distinct subjects and predicates. An example of a synthetic proposition would
be, "My father's brother has black hair."
held that all mathematical propositions are synthetic.
The American philosopher
W. V. O. Quine, in his "Two
Dogmas of Empiricism", famously challenged the distinction, arguing that the
two have a blurry boundary.
Specific theories of knowledge acquisition
In philosophy, empiricism is generally a theory of knowledge emphasizing the
role of experience, especially experience based on
observations by the five
forms treat all knowledge as empirical, while some regard disciplines such as
logic as exceptions.
Rationalists believe that knowledge is primarily (at least in some areas)
acquired by a priori processes or is
in the form of concepts not derived from experience. The relevant theoretical
processes often go by the name "intuition". The relevant theoretical concepts may purportedly
be part of the structure of the human
mind (as in
Kant's theory of
transcendental idealism), or they may be said to exist independently of the
mind (as in Plato's
theory of Forms).
The extent to which this innate human knowledge is emphasized over experience
as a means to acquire knowledge varies from rationalist to rationalist. Some
hold that knowledge of any kind can only be gained a priori, while others claim that some knowledge can also be
gained a posteriori. Consequently, the borderline between rationalist
epistemologies and others can be vague.
Constructivism is a view in philosophy according to which all knowledge is
"constructed" in as much as it is contingent on convention, human perception,
and social experience.knowledge
and truth that
forms a new
paradigm, based on inter-subjectivity instead of the classical
objectivity and viability instead of truth. Piagetian constructivism,
however, believes in objectivity as constructs can be validated through
experimentation. The constructivist point of view is pragmatic as
Vico said: "the truth is to have made it".
Constructivism proposes new definitions for
It originated in sociology under the term "social
constructionism" and has been given the name "constructivism" when referring
to philosophical epistemology, though "constructionism" and "constructivism" are
often used interchangeably. Constructivism has also emerged in the field of
International Relations, of which the writings of Alexander Wendt are most
popular. Describing the characteristic nature of International reality marked by
'anarchy' he says, "anarchy is what states make of it."
What do people know?
The last question that will be dealt with is the question of what people
know. At the heart of this area of study is
with many approaches involved trying to disprove some particular form of it.
Skepticism is related to the question of whether certain knowledge is
possible. Skeptics argue that the belief in something does not necessarily
justify an assertion of knowledge of it. In this skeptics oppose
foundationalism, which states that there have to be some basic beliefs that
are justified without reference to others. The skeptical response to this can
take several approaches. First, claiming that "basic beliefs" must exist,
amounts to the logical fallacy of
argument from ignorance combined with the
slippery slope. While a foundationalist would use
Münchhausen Trilemma as a justification for demanding the validity of basic
beliefs, a skeptic would see no problem with admitting the result
Developments from skepticism
For most of philosophical history, "knowledge" was taken to mean belief that
was true and justified to an absolute
certainty. Early in the 20th century, however, the notion that
belief had to be justified as such to count as knowledge lost favour.
Fallibilism is the view that knowing something does not entail certainty
Far from being purely academic, the study of epistemology is useful for a
great many applications. It is particularly commonly employed in issues of law
where proof of guilt or innocence may be required, or when it must be determined
whether a person knew a particular fact before taking a specific action (e.g.,
whether an action was premeditated).
Other common applications of epistemology include:
Encyclopedia of Philosophy, Volume 3, 1967, Macmillan, Inc.
Encyclopaedia Britannica Online, 2007
- ^ In
French, Portuguese and Spanish, to know a person is 'connaître',
'conhecer', 'conocer', whereas to know how to do something is 'savoir',
'saber', 'saber'. In Greek the verbs are ??????? (gnorízo) and
???? (kséro), respectively. In Italian the verbs are 'conoscere' and
'sapere' and the nouns for 'knowledge' are 'conoscenza' and 'sapienza',
respectively. In German, the verbs are "kennen" and "wissen." "Wissen"
implies knowing as a fact, "kennen" implies knowing in the sense of
being acquainted with and having a working knowledge of; there is also a
noun derived from "kennen", namely "erkennen", which roughly
implies knowledge in the form of recognition or acknowledgment. The verb
itself implies a process: you have to go from one state to another: from
a state of "not-erkennen" to a state of true erkennen.
This verb seems to be the most appropriate in terms of describing the
"episteme" in one of the modern European languages, hence the German
b Gettier, Edmund (1963). "Is
Justified True Belief Knowledge?". Analysis 23: 121–23.
Bimal Krishna Matilal (1986). Perception: An essay on Classical
Indian Theories of Knowledge. Oxford India 2002. The
Gettier problem is dealt with in Chapter 4, Knowledge as a mental
episode. The thread continues in the next chapter Knowing that
one knows. It is also discussed in Matilal's Word and the World
Robert Nozick (1981). Philosophical Explanations.
Harvard University Press. Philosophical
Explanations Chapter 3 "Knowledge and Skepticism" I. Knowledge
Conditions for Knowledge p. 172-178.
D. M. Armstrong (1973). Belief, Truth and Knowledge. Cambridge
References and further reading
- Annis, David. 1978. "A Contextualist Theory of Epistemic
Justification", in American Philosophical Quarterly, 15: 213-219.
- Boufoy-Bastick, Z. 2005. "Introducing 'Applicable Knowledge' as a
Challenge to the Attainment of Absolute Knowledge", Sophia Journal of
Philosophy, 8: 39-51.
- Bovens, Luc & Hartmann, Stephan. 2003. Bayesian Epistemology.
Oxford: Oxford University Press.
- Butchvarov, Panayot. 1970. The Concept of Knowledge.
Evanston, Northwestern University Press.
- Cohen, Stewart. 1998. "Contextualist Solutions to Epistemological
Problems: Scepticism, Gettier, and the Lottery." Australasian Journal
of Philosophy, 76: 289-306.
- Cohen Stewart. 1999. "Contextualism, Skepticism, and Reasons", in
- DeRose, Keith. 1992. "Contextualism and Knowledge Attributions",
Philosophy and Phenomenological Research, 15: 213-19.
- DeRose, Keith. 1999. "Contextualism: An Explanation and Defense", in
Greco and Sosa 1999.
- Feldman, Richard. 1999. "Contextualism and Skepticism", in Tomberlin
1999, pp. 91-114.
- Gettier, Edmund. 1963. "Is Justified True Belief Knowledge?",
Analysis, Vol. 23, pp. 121-23.
- Greco, J. & Sosa, E. 1999. Blackwell Guide to Epistemology,
Harris, Errol E. 1970. Hypothesis And Perception, George
Allen and Unwin, London, Reprinted 2002 Routledge, London.
- Harwood, Sterling. 1989. "Taking Skepticism Seriously -- And In
Context," Philosophical Investigations, Vol. 12.
- Hawthorne, John. 2005. "The Case for Closure", Contemporary
Debates in Epistemology, Peter Sosa and Matthias Steup (ed.): 26-43.
- Hendricks, Vincent F. 2006. Mainstream and Formal Epistemology,
New York: Cambridge University Press.
- Kant, Immanuel. 1781.
Critique of Pure Reason
- Keeton, Morris T. 1962. "Empiricism", in Dictionary of Philosophy,
Dagobert D. Runes (ed.), Littlefield, Adams, and Company, Totowa, NJ,
- Kirkham, Richard. 1984. "Does the Gettier Problem Rest on a
Mistake?" Mind, 93.
- Klein, Peter. 1981. Certainty: a Refutation of Scepticism,
Minneapolis, MN: University of Minnesota Press.
- Kyburg, H.E. 1961. Probability and the Logic of Rational Belief,
Middletown, CT: Wesleyan University Press.
- Korzybski, Alfred. 1994 (1933). Science and Sanity: An
Introduction to Non-Aristotelian Systems and General Semantics,
Fifth Edition. Ft. Worth, TX: Institute of General Semantics.
- Lewis, David. 1996. "Elusive Knowledge." Australian Journal of
Philosophy, 74, 549-67.
- Morin, Edgar. 1986. La Méthode, Tome 3, La Connaissance de la
connaissance (Method, 3rd volume : The knowledge of knowledge)
- Nelson, Quee, 2007. The Slightest Philosophy, Indianapolis, IN: Dog
Ear Publishing, 296 pages.
Niiniluoto, Ilkka, 2002. Critical Scientific Realism, Oxford:
Oxford Univ. Press.
Popper, Karl R. 1972. Objective Knowledge: An Evolutionary
Approach, Oxford: Oxford Univ. Press.
- Preyer, G./Siebelt, F./Ulfig, A. 1994. Language, Mind and
Epistemology, Dordrecht: Kluwer Academic Publishers.
- Rand, Ayn. 1979. Introduction to Objectivist Epistemology,
New York: Meridian.
- Russell, Bertrand. 1912. The Problems of Philosophy, New
York: Oxford University Press.
- Schiffer, Stephen. 1996. "Contextualist Solutions to Scepticism",
Proceedings of the Aristotelian Society, 96:317-33.
- Steup, Matthias. 2005. "Knowledge and Scepticism", Contemporary
Debates in Epistemology, Peter Sosa and Matthias Steup (eds.): 1-13.
- Tomberlin, James (ed.). 1999. Philosophical Perspectives 13,
Epistemology, Blackwell Publishing.
- Wittgenstein, Ludwig. 1922.
Tractatus Logico-Philosophicus, C.K. Ogden (trns.), Dover.
External links and references
Stanford Encyclopedia of Philosophy articles:
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