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Epistemology: the study of the nature, source, limits, and justification of knowledge. Sources of knowledge: Sense experience (empiricism) Reasoning alone (rationalism)
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Epistemology: the study of the nature, source, limits, and justification of knowledge • Sources of knowledge: • Sense experience (empiricism) • Reasoning alone (rationalism) • We truly know only that of which we are certain (a priori). Since sense experience (a posteriori knowledge) cannot guarantee certainty, reason alone must be the means for getting knowledge
Cartesian Doubt René Descartes (1596-1650) • Sense experiences are often wrong • I might be wrong about whether I have a body or if there is a world apart from my imagination (it may be a dream) • I might be wrong even about whether my reasoning abilities (e.g., 2+3=5) can be trusted (evil genius); so I should suspend judgment
Descartes’ Escape from Doubt • I cannot doubt that I am doubting (thinking). All other knowledge is based on the indubitable foundation that I exist: I think, therefore I exist (cogito ergo sum) • I know I exist imperfectly only by first knowing perfect existence (God); and as a perfect being, God would not deceive me or allow me to be deceived when I know something (e.g., wax) clearly and distinctly—that is, as an intelligible (e.g., mathematical) object
Objectionsto Descartes’ Method of Doubt • To doubt everything, we must doubt whether we are truly doubting, and that requires us to assume a public world of language users • Limiting knowledge only to what we know with certainty is too restrictive: we often know things not based on indubitable foundations • To reason that God guarantees one’s ability to reason is to assume exactly what we are trying to prove (the Cartesian Circle)