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Epistemology is the branch of philosophy that deals with the nature, origin and scope of knowledge. For a less academic treatment see methods of obtaining knowledge.

Philosophers of all schools of thought agree that people have the capacity to think of questions which seem to have no answers. For instance: Is there an end to time? Is there a God? Is the God of the philosophers the same as the Biblical God? Is there a reality beyond that which we can sense? Such questions are termed transcendental, because they currently go beyond the limits of rational inquiry. In the 20th century Logical Positivists have declared such metaphysical questions to be devoid of cognitive significance. But others continue to ask and search, or already have an answer -- epistemological beliefs which they prefer.

No consensus exists as to which epistemological beliefs will give human beings the most accurate understanding of the truth -- or even whether there is just one 'truth'. All people have epistemological beliefs, even if unconsciously, because thinking beings cannot understand and analyze ideas without first having a system to accept and process those ideas. All people - even children - possess rudimentary and undeveloped epistemological processes. However, those who study philosophy can begin to recognize how their own epistemologies work, and can develop their epistemology with new discoveries.

Many beliefs have positive epistemological features, and many beliefs are quite rational and quite justified. However, most people, at least in some moments, do not want to rest content with just being rational because even a rational belief can be false. To wit, one can be very conscious, careful, and logical in forming a belief, and so be rational in holding the belief; but it still might be false. Arguably, one's ultimate ambition for his or her beliefs is truth. Accordingly, when one is thinking about the epistemological features of one's beliefs, the overarching question is: When can someone say that his or her belief is the truth, and to what extent?

There are five major types of epistemological beliefs which address this question, and to my knowledge, no epistemology would be able to be sub-categorized into a sixth group; a short, but very important overview of each is on this page, with links to fuller descriptions of each. These are only general, and generally-accepted, groupings; also, many have non-epistemological meanings which won’t be discussed below (e.g., ethical, metaphysical, etc. meanings), but may be discussed on the full pages dedicated to each term.

Nihilists believe in nothing, and often, not even a reality, hence no truth to be examined.

Subjectivists claim that we are all unique individuals, hence we each see our own, subjective reality & truth. Constructivists further believe reality only consists of our (individual, subjective) concepts, whereas Intrinsicists believe there is a universal truth, and we just can’t see it, but agree that reality is conceptual, not concrete. Solipsists are extreme Constructivists, and near Nihilists, stating that they cannot know anyone else is real. Nominalists believe that our words and concepts are our way of simplifying our reality because we cannot observe, let alone digest, the totality of the overall, ‘true’ reality; e.g., search google for “Nietzsche WP 521,” then search for “WP 521”; ‘Perspectivism’ is also exhibited on the page; note that the “pencil” example acknowledges a possibility of common reality, whereas Constructivists would not. Conventionalists believe truth is determined by whatever the local, current social conventions are (whereas logicians call this an “ad populum” fallacy); Irrationalists combine subjectivity with an even stronger denunciation of logic.

Objectivists claim that we each have -- and claim the ability to rely upon -- senses such as logic (see Rationalism, below), emotions (Emotionalism; typically, with denunciation of logic, like the Irrationalists, above), external experiences (see Empiricism, below), logic AND experiences (see Logical Positivism, below), and/or Scientism (Logical Positivism plus humanities and social sciences) to see reality -- and that there is one, universal reality, regardless of anyone’s subjective view of it. Direct (‘naïve’) Realists might observe a standing tree one day, which has fallen the next, but not see it fall and thus be baffled what happened; yet, Indirect (‘representative’) Realism and Representationalists agree with many Subjectivists that you’re only able to perceive your concept of the tree, not a 100% clear pictureof the tree itself (due to: different: emotional attitude, position/location, past experiences, factual knowledge, and/or other senses/abilities); you’re also capable of building a concept to say, “The tree used to be standing; it must’ve fallen”; but you disagree with Subjectivists about whether the object you perceived was the truly there; i.e., subjective viewpoints of an objective reality.

Phenomenalism is an answer to George Berkeley's claim we can just say they don't exist. The idea claims everything is through the senses- we dont see the object, just our experience of it. Under phenomenalism when you say "a tree" you mean a certain perception of a brown shape. Small difference, but means we say nothing of a tree- just the perception. The idea says we shouldn't think of objects as things we can't see, with substance, which then interact with our senses and give us representations of it. Phenomenalism also claims things don't necessarily just not exist, they exist as permanent possibilities of experience.Phenomenalists like Ayer said if statements cannot be confirmed by sense experience then they were literally non-sensical.(from Groovyweb with permission)

Mysticists claim that there are more than 5 senses, or special powers, etc., which allow further insights into reality/truth if only they are tapped. So can some Irrationalists and Intuitionists (see above).

Skeptics are undecided regarding all of the above philosophies. Skeptics claim, to varying degrees, that we either do not, or cannot, have knowledge, and/or certainty of that knowledge. Fallibilism is the belief that because mankind is apparently FALLIBLE and not omniscient, skepticism about our own beliefs is rationally merited (but Fallibilism and Agnosticism often refer only to a skepticism about god(s)). Pyrrhonism is an early, Eastern-inspired form of skepticism. Probabilism is a belief that although we can’t be certain, we should make choices/beliefs which seem most PROBABLY the best to us, with some scientists even trying to quantify some types of probabilities. Aside from Probabilists, most Skeptics don't assert their own theories, rather, challenging the others to prove the beliefs they assert as truth; a famous proposition is the assertion that a deity or superhuman race (aliens??) COULD manipulate our sensory perceptions; human scientists are even causing ociception in rats today using micro chips (source:, so the idea is possible, justifying their wait-n-see attitudes.
...More info, with graphic explanations of how most groups see an actual object vs. a "perception" of that object, etc., are at:

An analysis of this topic might make one wonder, "How can I be sure that my beliefs are true? Is there any guarantee available to me -- some sort of criteria I might use -- in order to decide, as well and as carefully as I possibly could, that indeed what I believe is actually true?"

Suppose someone thought that his or her belief had been arrived at rationally, Using logic, one might base his or her belief on observation and experiment, conscientiously answer objections, and so forth. Accordingly, one would conclude that his or belief is rational. If so, then one's belief has at least some claim to be true. Rationality provides an indicator of truth: if your belief is rational, then it is at least probably true. At the very least, the rationality of a belief gives reason to think the belief is true.

Some examples of the many debates between different schools of epistemology follow:

People approach epistemology in various ways; the following categories originally reflected divisions among schools of philosophy in the seventeenth and eighteenth centuries, but may prove useful in categorizing certain approximate trends throughout the history of epistemology:

(1) Rationalists believe there are innate ideas that are not found in experience. These ideas exist independently of any experience people may have. These ideas may in some way derive from the structure of the human mind, or they may exist independently of the mind. If they exist independently, they may be understood by a human mind once it reaches a necessary degree of sophistication.

(2) Empiricists (see: scientific method, philosophy of science naive empiricism) deny that there are concepts that exist prior to experience. For them, all knowledge is a product of human learning, based on human perception. Perception, however, may cause concern, since illusions, misunderstandings, and hallucinations prove that perception does not always depict the world as it really is.

Some say the existence of mathematical theorems poses a problem for empiricists. Mathematical truths certainly do not depend on experience, and they can be known prior to experience. Some empiricists reply that all mathematical theorems are empty of cognitive content, as they only express the relationship of concepts to one another. Rationalists would hold that such relationships are indeed a form of cognitive content.

(3) The German philosopher Immanuel Kant is widely understood as having worked out a synthesis between these views. In Kant's view people certainly do have knowledge that is prior to experience, which is not devoid of cognitive significance. For example, the principle of causality. He held that there are a priori synthetic concepts.

(4) Logical Positivism is also seen as accepting both Rationalism (logical) and Empiricism (Positivism); it also often stresses a denunciation of Emotionalism (see above).

Epistemologists spend a great deal of time concerning themselves with various epistemic features of belief, such as justification and rationality. And they write long articles and books trying to say just when beliefs are justified, or rational. A related concern is where such epistemic features ultimately come from. If one says, for example, that his or her belief that Paris is the capital of France is justified, one can ask: Where did the justification for that belief come from? This information could have come from a reliable source of testimony. Another source of justification would be sense-perception. So epistemology asks: What are the ultimate sources of justification, rationality, or other epistemic features of our other beliefs? And that allows one to answer a further question: What are the ultimate sources of knowledge? Which brings one to the question of what knowledge is. The question here is not what one can know, or even what one does know. The question is: What would knowledge be, if one had it? A belief has to pass some sort of muster to count as knowledge. So what features would a belief have to have, in order to be an actual piece of knowledge -- not just something that pretends to be knowledge, but which is actually knowledge?

Another contemporary approach to epistemology divides the approaches into two categories: foundationalism and coherentism.

Foundationalism holds that there are basic beliefs in which you can be certain and that you can be similarly confident in other beliefs derived rigorously from these. The most famous example of this is Descartes' statement cogito ergo sum ("I think therefore I am"), by which he meant that it is impossible to doubt one's own existence. Others have responded that a person's observation of his or her own mental activity is not fundamentally different or more reliable than other observations and does not necessarily imply a thinker. The difficulty of foundationalism is that no set of basic beliefs proposed for it are uncontroversial.

Coherentism holds that you are more justified in beliefs if they form a coherent whole with your other beliefs. A common, cheeky, riposte to this is called the "drunken sailors" argument, which points out that two drunken sailors holding each other up may still not be on solid ground. Stated more formally: a set of beliefs can be internally consistent but still not reflect the actual world.

Recently, Susan Haack has attempted to fuse these two approaches into her doctrine of Foundherentalism, which accrues degrees of relative confidence to beliefs by mediating between the two approaches. She covers this in her book Evidence and Inquiry: Towards Reconstruction in Epistemology.

There is also Reliabilism where one makes predictions from what usually happens. (Eg. claiming to speak russian can be proved by a russian speaker) There are two methods of reliable justification: External- (Reliable, eg. a doctor diagnosing me)and Internal- (Unreliable, eg. relying on sensations from my internal organs) But how do we know that something that is reliable is right? A computer with a bug in it is reliably incorrect.

See also: Self-evidence, theory of justification, the regress argument in epistemology, a priori and a posteriori knowledge, knowledge, scepticism, Common sense and the Diallelus, social epistemology, aesthetics, ethics, metaphysics, philosophy, ontology, reason, philosophy of science, science education, epistemology, A_priori, A_posteriori.

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