Knowledge is a familiarity with someone or something, which can include facts, information, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject. It can be implicit (as with practical skill or expertise) or explicit (as with the theoretical understanding of a subject); it can be more or less formal or systematic. In philosophy, the study of knowledge is called epistemology; the philosopher Plato famously defined knowledge as "justified true belief." However, no single agreed upon definition of knowledge exists, though there are numerous theories to explain it. The following quote from Bertrand Russell's "Theory of Knowledge" illustrates the difficulty in defining knowledge: "The question how knowledge should be defined is perhaps the most important and difficult of the three with which we shall deal. This may seem surprising: at first sight it might be thought that knowledge might be defined as belief which is in agreement with the facts. The trouble is that no one knows what a belief is, no one knows what a fact is, and no one knows what sort of agreement between them would make a belief true. Let us begin with belief."
Knowledge acquisition involves complex cognitive processes: perception, communication, association and reasoning; while knowledge is also said to be related to the capacity of acknowledgment in human beings.
|“||The eventual demarcation of philosophy from science was made possible by the notion that philosophy's core was "theory of knowledge," a theory distinct from the sciences because it was their foundation… Without this idea of a "theory of knowledge," it is hard to imagine what "philosophy" could have been in the age of modern science.||”|
— Richard Rorty, Philosophy and the Mirror of Nature
The definition of knowledge is a matter of on-going debate among philosophers in the field of epistemology. The classical definition, described but not ultimately endorsed by Plato, specifies that a statement must meet three criteria in order to be considered knowledge: it must be justified, true, and believed. Some claim that these conditions are not sufficient, as Gettier case examples allegedly demonstrate. There are a number of alternatives proposed, including Robert Nozick's arguments for a requirement that knowledge 'tracks the truth' and Simon Blackburn's additional requirement that we do not want to say that those who meet any of these conditions 'through a defect, flaw, or failure' have knowledge. Richard Kirkham suggests that our definition of knowledge requires that the evidence for the belief necessitates its truth.
In contrast to this approach, Wittgenstein observed, following Moore's paradox, that one can say "He believes it, but it isn't so," but not "He knows it, but it isn't so."  He goes on to argue that these do not correspond to distinct mental states, but rather to distinct ways of talking about conviction. What is different here is not the mental state of the speaker, but the activity in which they are engaged. For example, on this account, to know that the kettle is boiling is not to be in a particular state of mind, but to perform a particular task with the statement that the kettle is boiling. Wittgenstein sought to bypass the difficulty of definition by looking to the way "knowledge" is used in natural languages. He saw knowledge as a case of a family resemblance. Following this idea, "knowledge" has been reconstructed as a cluster concept that points out relevant features but that is not adequately captured by any definition.
Symbolic representations can be used to indicate meaning and can be thought of as a dynamic process. Hence the transfer of the symbolic representation can be viewed as one ascription process whereby knowledge can be transferred. Other forms of communication include observation and imitation, verbal exchange, and audio and video recordings. Philosophers of language and semioticians construct and analyze theories of knowledge transfer or communication.
While many would agree that one of the most universal and significant tools for the transfer of knowledge is writing (of many kinds), argument over the usefulness of the written word exists nonetheless, with some scholars skeptical of its impact on societies. In his collection of essays Technopoly, Neil Postman demonstrates the argument against the use of writing through an excerpt from Plato's work Phaedrus (Postman, Neil (1992) Technopoly, Vintage, New York, pp 73). In this excerpt the scholar Socrates recounts the story of Thamus, the Egyptian king and Theuth the inventor of the written word. In this story, Theuth presents his new invention "writing" to King Thamus, telling Thamus that his new invention "will improve both the wisdom and memory of the Egyptians" (Postman, Neil (1992) Technopoly, Vintage, New York, pp 74). King Thamus is skeptical of this new invention and rejects it as a tool of recollection rather than retained knowledge. He argues that the written word will infect the Egyptian people with fake knowledge as they will be able to attain facts and stories from an external source and will no longer be forced to mentally retain large quantities of knowledge themselves (Postman, Neil (1992) Technopoly, Vintage, New York,pp 74).
Andrew Robinson also highlights, in his work The Origins of Writing, the possibility for writing to be used to spread false information and therefore the ability of the written word to decrease social knowledge (Robinson, Andrew (2003) The Origins of Writing in Crowley and Heyer (eds) Communication in History: Technology, Culture, Society, Boston pp 34). People are often internalizing new information which they perceive to be knowledge but in reality fill their minds with false knowledge.
The above points are moot in the modern world. Verbal communication lends itself to the spread of falsehoods much more so than written, as there is no record of exactly what was said or who originally said it (usually neither the source nor the content can be verified). Gossip and rumors are common examples. As to value of writing, the extent of human knowledge is now so great that it is only possible to record it and to communicate it through writing. Major libraries today can have millions of books of knowledge (in addition to works of fiction). It is only recently that audio and video technology for recording knowledge have become available and the use of these still requires replay equipment and electricity. Verbal teaching and handing down of knowledge is limited to those few who would have contact with the transmitter person - far too limited for today's world. Writing is still the most available and most universal of all forms of recording and transmitting knowledge. It stands unchallenged as mankind's primary technology of knowledge transfer down through the ages and to all cultures and languages of the world.
Situated knowledge is knowledge specific to a particular situation. It is a term coined by Donna Haraway as an extension of the feminist approaches of “successor science” suggested by Sandra Harding, one which “offers a more adequate, richer, better account of a world, in order to live in it well and in critical, reflexive relation to our own as well as others’ practices of domination and the unequal parts of privilege and oppression that makes up all positions.” This situation partially transforms science into a narrative, which Arturo Escobar explains as, “neither fictions nor supposed facts.” This narrative of situation is historical textures woven of fact and fiction, and as Escobar explains further, “even the most neutral scientific domains are narratives in this sense,” insisting that rather than a purpose dismissing science as a trivial matter of contingency, “it is to treat (this narrative) in the most serious way, without succumbing to its mystification as ‘the truth’ or to the ironic skepticism common to many critiques.”
Haraway’s argument stems from the limitations of the human perception, as well as the overemphasis of the sense of vision in science. According to Haraway, vision in science has been, “used to signify a leap out of the marked body and into a conquering gaze from nowhere.” This is the “gaze that mythically inscribes all the marked bodies, that makes the unmarked category claim the power to see and not be seen, to represent while escaping representation.” This causes a limitation of views in the position of science itself as a potential player in the creation of knowledge, resulting in a position of “modest witness”. This is what Haraway terms a “god trick”, or the aforementioned representation while escaping representation. In order to avoid this, “Haraway perpetuates a tradition of thought which emphasizes the important of the subject in terms of both ethical and political accountability” .
Some methods of generating knowledge, such as trial and error, or learning from experience, tend to create highly situational knowledge. One of the main attributes of the scientific method is that the theories it generates are much less situational than knowledge gained by other methods. Situational knowledge is often embedded in language, culture, or traditions. This integration of situational knowledge is an allusion to the community, and its attempts at collecting subjective perspectives into an embodiment “of views from somewhere.” 
Knowledge generated through experience is called knowledge "a posteriori", meaning afterwards. The pure existence of a term like "a posteriori" means this also has a counterpart. In this case that is knowledge "a priori", meaning before. The knowledge prior to any experience means that there are certain "assumptions" that one takes for granted. For example if you are being told about a chair it is clear to you that the chair is in space, that it is 3D. This knowledge is not knowledge that one can "forget", even someone suffering from amnesia experiences the world in 3D.
Even though Haraway’s arguments are largely based on feminist studies, this idea of different worlds, as well as the skeptic stance of situated knowledge is present in the main arguments of post-structuralism. Fundamentally, both argue the contingency of knowledge on the presence of history; power, and geography, as well as the rejection of universal rules or laws or elementary structures; and the idea of power as an inherited trait of objectification.
One discipline of epistemology focuses on partial knowledge. In most cases, it is not possible to understand an information domain exhaustively; our knowledge is always incomplete or partial. Most real problems have to be solved by taking advantage of a partial understanding of the problem context and problem data, unlike the typical math problems one might solve at school, where all data is given and one is given a complete understanding of formulas necessary to solve them.
This idea is also present in the concept of bounded rationality which assumes that in real life situations people often have a limited amount of information and make decisions accordingly.
The development of the scientific method has made a significant contribution to how knowledge is acquired. To be termed scientific, a method of inquiry must be based on gathering observable and measurable evidence subject to specific principles of reasoning and experimentation. The scientific method consists of the collection of data through observation and experimentation, and the formulation and testing of hypotheses. Science, and the nature of scientific knowledge have also become the subject of Philosophy. As science itself has developed, knowledge has developed a broader usage which has been developing within biology/psychology—discussed elsewhere as meta-epistemology, or genetic epistemology, and to some extent related to "theory of cognitive development".
Note that "epistemology" is the study of knowledge and how it is acquired. Science is "the process used everyday to logically complete thoughts through inference of facts determined by calculated experiments." Sir Francis Bacon was critical in the historical development of the scientific method; his works established and popularized an inductive methodology for scientific inquiry. His famous aphorism, "knowledge is power", is found in the Meditations Sacrae (1597).
Until recent times, at least in the Western tradition, it was simply taken for granted that knowledge was something possessed only by humans — and probably adult humans at that. Sometimes the notion might stretch to (ii) Society-as-such, as in (e.g.) "the knowledge possessed by the Coptic culture" (as opposed to its individual members), but that was not assured either. Nor was it usual to consider unconscious knowledge in any systematic way until this approach was popularized by Freud.
Other biological domains where "knowledge" might be said to reside, include: (iii) the immune system, and (iv) in the DNA of the genetic code. See the list of four "epistemological domains": Popper, (1975); and Traill (2008: Table S, page 31)—also references by both to Niels Jerne.
Such considerations seem to call for a separate definition of "knowledge" to cover the biological systems. For biologists, knowledge must be usefully available to the system, though that system need not be conscious. Thus the criteria seem to be:
Scientific knowledge may not involve a claim to certainty, maintaining skepticism means that a scientist will never be absolutely certain when they are correct and when they are not. It is thus an irony of proper scientific method that one must doubt even when correct, in the hopes that this practice will lead to greater convergence on the truth in general.
In many expressions of Christianity, such as Catholicism and Anglicanism, knowledge is one of the seven gifts of the Holy Spirit.
The Old Testament's tree of the knowledge of good and evil contained the knowledge that separated Man from God: "And the LORD God said, Behold, the man is become as one of us, to know good and evil…" (Genesis 3:22)
In Gnosticism divine knowledge or gnosis is hoped to be attained. In Thelema knowledge and conversation with one's Holy Guardian Angel is the purpose of life.
विद्या दान (Vidya Daan) i.e. knowledge sharing is a major part of Daan, a tenet of all Dharmic Religions. Hindu Scriptures present two kinds of knowledge, Paroksh Gyan and Prataksh Gyan. Paroksh Gyan (also spelled Paroksha-Jnana) is secondhand knowledge: knowledge obtained from books, hearsay, etc. Prataksh Gyan (also spelled Prataksha-Jnana) is the knowledge borne of direct experience, i.e., knowledge that one discovers for oneself. Jnana yoga ("path of knowledge") is one of three main types of yoga expounded by Krishna in the Bhagavad Gita. (It is compared and contrasted with Bhakti Yoga and Karma yoga.)
In Islam, knowledge (Arabic: علم, ʿilm) is given great significance. "The Knowing" (al-ʿAlīm) is one of the 99 names reflecting distinct attributes of God. The Qur'an asserts that knowledge comes from God (2:239) and various hadith encourage the acquisition of knowledge. Muhammad is reported to have said "Seek knowledge from the cradle to the grave" and "Verily the men of knowledge are the inheritors of the prophets". Islamic scholars, theologians and jurists are often given the title alim, meaning "knowledgable".
In Jewish tradition, knowledge (Hebrew: דעת da'ath) is considered one of the most valuable traits a person can acquire. Observant Jews recite three times a day in the Amidah "Favor us with knowledge, understanding and discretion that come from you. Exalted are you, Existent-One, the gracious giver of knowledge." The Tanakh states, "A wise man gains power, and a man of knowledge maintains power", and "knowledge is chosen above gold".
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