is defined Oxford English Dictionary variously as (i) facts, information, and skills acquired by a person through experience or education; the theoretical or practical understanding of a subject, (ii) what is known in a particular field or in total; facts and information or (iii) awareness or familiarity gained by experience of a fact or situation. Philosophical debates in general start with Plato's formulation of knowledge as "justified true belief". There is however no single agreed definition of knowledge presently, nor any prospect of one, and there remain numerous competing theories.
Knowledge acquisition involves complex cognitive processes: perception, learning, communication, association, and reasoning. The term knowledge is also used to mean the confident understanding of a subject, potentially with the ability to use it for a specific purpose.
The definition of knowledge is a matter of on-going debate among philosophers. The classical definition is found in, but not ultimately endorsed by, Plato., has it that in order for there to be knowledge at least three criteria must be fulfilled; that in order to count as knowledge, a statement 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 believer's evidence is such that it logically necessitates the truth of the belief.
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.
In An Introduction to Logic and Scientific Method (1934), Morris R. Cohen and Ernest Nagel reviewed the pursuit of truth as determined by logical considerations. They reviewed ways of eliminating doubt and arriving at stable beliefs or reliable knowledge, such as
- The method of authority
- The method of intuition
- The methods of experimental inquiry:
- Types of invariant relations
- The experimental method in general
- The method of agreement
- The method of difference
- The joint method of agreement and difference
- The method of concomitant variation
- The doctrine of the uniformity of nature
- The plurality of causes
Their final conclusion was, "Scientific method we declare as the most assured technique man has yet devised for controlling the flux of things and establishing stable beliefs."
In an essay entitled "Inductive Method and Scientific Discovery," Marcello Pera said, "In the first place, the scientific method is a procedure, a general strategy that indicates an ordered sequence of moves (or steps) which the scientist has to make (or go through) in order to reach the goal of his research." (In On Scientific Discovery, edited by Grmek, Cohen, and Cimino , published in the Boston Studies in the Philosophy of Science Series.) The scientific method is not a method directly applied, but rather a guide to the mental activity stages of originating, refining, extending, and applying knowledge. It is subject neutral and flexible in use; it is thus suitable for all domains.
Statements about truth must be viewed skeptically. Rather than state something as "true," the following phrase should be used: "On the evidence available today the balance of probability favors the view that..." (V. Gordon Childe, Man Makes Himself, 1936)
The literature contains hundreds of formulas for the scientific method. They are basically the same but differ in length and terminology. In an article "Suggestions for Teaching the Scientific Method" published in the March 1961 issue of American Biology Teacher, Dr. Kenneth B.M. Crooks suggested this one:
- Is there a problem?
- Get the evidence
- Attributes needed
- Weigh all evidence
- Make the educated guess (hypothesis)
- Challenge the hypothesis
- Get a conclusion
- Suspend judgment
- Deductive reasoning
Symbolic representations can be used to store meaning. The mapping from the symbolic representation to meaning can be thought of as a dynamic process. Hence also the transfer of the symbolic representation can be viewed as an ascription process whereby knowledge can be transferred. We talk of 'data' (the symbols) and 'information' (the meaning). Knowledge is contextual however, so explanation and investigation is usually needed to transfer appropriate state information around which an appropriate interpretation can be established — in the case of two entities, a 'conversation' ensues during which 'understanding' can be developed.
Situated knowledge is knowledge specific to a particular situation. Imagine two very similar breeds of mushroom, which grow on either side of a mountain, one nutritious, one poisonous. Relying on knowledge from one side of an ecological boundary, after crossing to the other, may lead to starving rather than eating perfectly healthy food near at hand, or to poisoning oneself by mistake.
Some methods of generating knowledge, such as trial and error, or learning from experience, tend to create highly situational knowledge. One of the main benefits 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.
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 one is being told about a chair it is clear to him 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. See also: A priori and a posteriori.
One discipline of epistemology focusses on partial knowledge. In most realistic cases, it is not possible to have an exhaustive understanding of an information domain, so then we have to live with the fact that our knowledge is always not complete, that is, partial. Most real problems have to be solved by taking advantage of a partial understanding of the problem context and problem data. That is very different from the typical simple math problems that we solve at school, where all data are given and we have a perfect understanding of formulas necessary to solve them.
Knowledge management is a management theory which emerged in the 1990s. It seeks to understand the way in which knowledge is created, used and shared within organizations. A significant part of Knowledge Management theory and practice aligns two models: (i) the DIKW model, which places data, information, knowledge and wisdom into an increasingly useful pyramid. (ii) Nonaka's reformulation of Polanyi's distinction between tacit and explicit knowledge. Both of these models are increasingly under challenge with different schools of thought emerging which are more fully described and referenced in the main article.
An objective of mainstream knowledge management is to ensure that the right information is delivered to the right person just in time, in order to take the most appropriate decision. In that sense, knowledge management is not interested in managing knowledge per se, but to relate knowledge and its usage. This leads to Organizational Memory Systems. More recent developments have focused on managing networks (the flow of knowledge rather than knowledge itself) and narrative forms of knowledge exchange.
Religious meaning of knowledge
Hindu Scriptures say two kinds of knowledge. Paroksha Gnyana and Aporoksha Gnyana. Paroksha Gnyana is knowledge that is second hand , the knowledge that is obtained from books , from heresay etc. Aporoksha Gnyana is the knowledge borne of direct experience, i.e. the knowledge that one discovers for himself. 
- In Plato's Theaetetus, Socrates and Theaetetus discuss three definitions of knowledge: knowledge as nothing but perception, knowledge as true judgment, and, finally, knowledge as a true judgment with an account. Each of these definitions are shown to be unsatisfactory.
- Ludwig Wittgenstein, On Certainty, remark 42
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