Epistemology

Epistemology is concerned with the nature and scope of knowledge,[11] such as the relationships between truth, belief, and theories of justification.

Skepticism is the position which questions the possibility of completely justifying any truth. The regress argument, a fundamental problem in epistemology, occurs when, in order to completely prove any statement P, its justification itself needs to be supported by another justification. This chain can do three possible options, all of which are unsatisfactory according to the Münchhausen Trilemma. One option is infinitism, where this chain of justification can go on forever. Another option is foundationalism, where the chain of justifications eventually relies on basic beliefs or axioms that are left unproven. The last option, such as in coherentism, is making the chain circular so that a statement is included in its own chain of justification.

Rationalism is the emphasis on reasoning as a source of knowledge. Empiricism is the emphasis on observational evidence via sensory experience over other evidence as the source of knowledge. Rationalism claims that every possible object of knowledge can be deduced from coherent premises without observation. Empiricism claims that at least some knowledge is only a matter of observation. For this, Empiricism often cites the concept of tabula rasa, where individuals are not born with mental content and that knowledge builds from experience or perception. Epistemological solipsism is the idea that the existence of the world outside the mind is an unresolvable question.

René Descartes

Parmenides (fl. 500 BC) argued that it is impossible to doubt that thinking actually occurs. But thinking must have an object, therefore something beyond thinking really exists. Parmenides deduced that what really exists must have certain properties—for example, that it cannot come into existence or cease to exist, that it is a coherent whole, that it remains the same eternally (in fact, exists altogether outside time). This is known as the third man argument. Plato (427–347 BC) combined rationalism with a form of realism. The philosopher's work is to consider being, and the essence (ousia) of things. But the characteristic of essences is that they are universal. The nature of a man, a triangle, a tree, applies to all men, all triangles, all trees. Plato argued that these essences are mind-independent "forms", that humans (but particularly philosophers) can come to know by reason, and by ignoring the distractions of sense-perception.

Modern rationalism begins with Descartes. Reflection on the nature of perceptual experience, as well as scientific discoveries in physiology and optics, led Descartes (and also Locke) to the view that we are directly aware of ideas, rather than objects. This view gave rise to three questions:

Is an idea a true copy of the real thing that it represents? Sensation is not a direct interaction between bodily objects and our sense, but

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