Epistemology: the study of the nature, source, limits, & justification of knowledge Rationalism: we truly know only that of which we are certain. Since sense experience cannot guarantee certainty, reason alone must be the means for getting knowledge Real knowledge about ourselves and the world is a priori (prior to and independent of experience). “Knowledge” gained from sense experience (a posteriori) is guaranteed only by appeal to reason

Rationalism: Sense Experience Does Not Provide Knowledge Shankara: we correct our experiences of self and world (e.g., hallucinations, sense perceptions) by knowing the oneness of ultimate reality (Brahman) (788-822) Descartes: 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), and even whether my reasoning abilities (e.g., 2+3=5) can be trusted (evil genie)

Objections to Descartes’ Method of Doubt Even if some sense experiences are mistaken, that is no reason to doubt (even hypothetically) all of them Limiting knowledge only to what we know with certainty is too restrictive: we often know things a posteriori (i.e., based on experience), not on indubitable foundations If we doubt everything, we must also doubt whether we are truly doubting—which requires us to assume the existence of a public world of language users

Descartes’ Escape from Doubt I cannot doubt that I am doubting (thinking). All other knowledge is based on the undoubtable 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

Innate Ideas: knowledge of ideas or principles is possible only if they are inborn Plato: our knowledge of certain propositions is based on remembering truths acquired before our birth Leibniz: our recognition of ideas and truths is based on innate dispositions of the mind Jainism: past unethical behavior blinds us to our innate knowledge of all things