Epistemology or theory of knowledge is the branch of philosophy that studies the nature, methods, limitations, and validity of knowledge and belief.

The term "epistemology" is based on the Greek words "επιστήμη or episteme" (knowledge or science) and "λόγος or logos" (reason).[1] It was introduced into English by the Scottish philosopher James Frederick Ferrier (1808-1864).[2]
Much of the debate in this field has focused on analyzing the nature of knowledge and how it relates to similar notions such as truth, belief, and 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?".


 Knowledge
The primary question that epistemology addresses is "What is knowledge?". This question is several millennia old.

 Distinguishing knowing that from knowing how
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. Or, one knows how to ride a bicycle and one knows that a bicycle has two wheels.

Philosophers thus distinguish between theoretical reason (knowing that) and practical reason (knowing how), with epistemology being interested primarily in theoretical knowledge. This distinction is recognised linguistically in many languages but not in English. In French (as well as in Portuguese and Spanish), for example, to know a person is 'connaître' ('conhecer' / 'conocer'), whereas to know how to do something is 'savoir' ('saber' in both Portuguese and Spanish). In Greek language the verbs are γνωρίζω (gnorízo) and ξέρω (kséro), respectively. In Italian the verbs are 'conoscere' and 'sapere' and the nouns for 'knowledge' are 'conoscenza' and 'sapienza', respectively. In the German language, it is exemplified with the verbs "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. But neither of those verbs do truly extend to the full meaning of the subject of epistemology. In German, there is also a verb derived from "kennen", namely "erkennen", which roughly implies knowledge in the form of recognition or acknowledgment, strictly metaphorically. 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 name "Erkenntnistheorie."

 Belief

Sometimes, when people say that they believe in something, what they mean is that they predict that it will prove to be useful or successful in some sense — perhaps someone 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, as such, is where "to believe something" simply means any cognitive content held as true — e.g., to believe that the sky is blue is to think that the proposition, "The sky is blue," is true.
Knowledge implies belief. Consider the statement, "I know P, but I don't believe that P is true." This statement is contradictory. To know P is, among other things, to believe that P is true, i.e. to believe in P. (See the article on Moore's paradox.)

 Truth

If someone believes something, they think that it is true, but they may be mistaken. This is not the case with knowledge. For example, suppose that Jeff thinks that a particular bridge is safe, and attempts to cross it; unfortunately, the bridge collapses under his weight. We might say that Jeff 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. For something to count as knowledge, it must actually be true.

 Justification

 Plato

Main article: Theaetetus (dialogue)
In Plato's dialogue Theaetetus, Socrates 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 she will recover from her illness quickly. Nevertheless, even if this belief turned out to be true, the patient would not have known that she would get well since 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

In 1963 Edmund Gettier called into question the theory of knowledge that had been dominant among philosophers for thousands of years[3]. 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 two 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."(see [3] p.122.)

 Responses to Gettier

The responses to Gettier have been varied. Usually, responses to Gettier 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.

 Infallibilism, indefeasibility

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.[citation needed] 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 Navya-Nyaya 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 view of 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." [4]

 Reliabilism

Reliabilism is a theory advanced by philosophers such as Alvin 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 barn-like buildings 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.[citation needed]

 Other responses
The American philosopher Robert Nozick has offered the following definition of knowledge:
S knows that P if and only if:
P;
S believes that P;
if P were false, S would not believe that P;
if P is true, S will believe that P. [5]
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[6]: 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 subjunctive condition.
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."[citation needed]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 sui 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
Main article: Internalism and externalism
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 gain knowledge.

 Acquiring knowledge
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 experience and apriority as means of creating knowledge and that between synthesis and analysis as means of proof, and debates such as the one between empiricists and rationalists.

 The regress problem
Main article: Regress argument
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 skepticism. The skeptic will argue that since no one can complete such a chain, ultimately no beliefs are justified and, therefore, no one knows anything.

 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.

 Infinitism
Some philosophers, notably Peter 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 and coherentism.

 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.[citation needed] 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

 Coherentism
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 circularity, 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.

 Foundherentism
There is also a position known as "foundherentism". Susan 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.[citation needed]

 A priori and a posteriori knowledge
Main article: A priori and a posteriori (philosophy)
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).

 Analytic/synthetic distinction
Main article: Analytic/synthetic distinction
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." Kant 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

 Empiricism

In philosophy generally, empiricism is a theory of knowledge emphasizing the role of experience, especially experience based on perceptual observations by the five senses. Certain forms treat all knowledge as empirical, while some regard disciplines such as mathematics and logic as exceptions.

 Rationalism

Rationalists believe that knowledge is primarily (at least in some areas) acquired by a priori processes or is innate—e.g., in the form of concepts not derived from experience. The relevant theoretical processes often go by the name "intuition".[citation needed] 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,[citation needed] while others claim that some knowledge can also be gained a posteriori.[citation needed] Consequently, the borderline between rationalist epistemologies and others can be vague.

 Constructivism

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.[citation needed] Constructivism proposes new definitions for knowledge and truth that forms a new paradigm, based on inter-subjectivity instead of the classical objectivity and viability instead of truth. The constructivist point a view is pragmatic as Vico said: "the truth is to have made it".
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.[citation needed]

 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 scepticism, with many approaches involved trying to disprove some particular form of it.

 Scepticism
Main article: Philosophical scepticism
Scepticism is related to the question of whether certain knowledge is possible. Sceptics argue that the belief in something does not necessarily justify an assertion of knowledge of it. In this sceptics oppose foundationalism, which states that there have to be some basic beliefs that are justified without reference to others. The sceptical 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 Munchhausen-Trilemma as a justification for demanding the validity of basic beliefs, a sceptic would see no problem with admitting the result.

 This short section requires expansion.

 Responses to scepticism

 Contextualism

Contextualism in epistemology is the claim that knowledge varies with the context in which it is attributed. More precisely, contextualism is the claim that, in a sentence of the form, "S knows that P," the relation between S and P depends on the context of discussion. According to the contextualist, the term "knows" is context-sensitive in a way similar to words such as "poor", "tall", and "flat". (Opposed to this contextualism are several forms of what is called "invariantism", the theory that the meaning of the term "knowledge", and hence the proposition expressed by the sentence, "S knows that P," does not vary from context to context.) The motivation behind contextualism is the idea that, in the context of discussion with an extreme sceptic about knowledge, there is a very high standard for the accurate ascription of knowledge, while in ordinary usage, there is a lower standard. Hence, contextualists attempt to evade sceptical conclusions by maintaining that sceptical arguments against knowledge are not relevant to our ordinary usages of the term.

 Fallibilism

For most of philosophical history, "knowledge" was taken to mean belief that was true and justified to an absolute certainty.[citation needed] 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 regarding it.

 Practical applications
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:
Mathematics and science
History and archaeology
Medicine (diagnosis of disease)
Product testing (How can we know that the product will not fail?)
Intelligence (information) gathering
Religion and Apologetics
Cognitive Science
Artificial Intelligence
Psychology
Linguistics
Literature
Philosophy
Knowledge Management
Testimony

 Intercultural References
In Indian philosophy, the Sanskrit term for the equivalent branch of study is "pramana."[7][8]