 Locke According to Locke—following a tradition which can be traced back to the ancient (Democritus) and modern (Galileo Galilei, Isaac Newton) atomism—some sense-data, namely the sense-data of secondary qualities (i.e. colours, tastes, smells, sounds), do not represent anything in the external world, even if they are caused by external qualities (primary qualities). Thus it is natural to adopt a theory of critical realism. By its talk of sense-data and representation, this theory depends on or presupposes the truth of representationalism. If critical realism is correct, then representationalism would have to be a correct theory of perception. Descartes René Descartes developed the theory that, since we could not definitely prove anything we experienced, the only thing which is sure to exist is our mind. He explains this by stating that in order to experience anything - real or fake - we first have to exist at all. That led to his famous quote "Cogito, ergo sum." (I think, therefore I am.). See also  New realism (philosophy) 
Some precursors Locke According to Locke—following a tradition which can be traced back to the ancient (Democritus) and modern (Galileo Galilei, Isaac Newton) atomism—some sense-data, namely the sense-data of secondary qualities (i.e. colours, tastes, smells, sounds), do not represent anything in the external world, even if they are caused by external qualities (primary qualities). By its talk of sense-data and representation, this theory depends on or presupposes the truth of representationalism. Descartes René Descartes developed the theory that, since we could not definitely prove anything we experienced, the only thing which is sure to exist is our mind. He explains this by stating that in order to experience anything — real or fake — we first have to exist at all. That led to his famous saying "Cogito, ergo sum." (I think, therefore I am.). See also Anti-realism Critical realism (philosophy of the social sciences) New realism (philosophy) Subtle realism
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Some precursors
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Thus it is natural to adopt a theory of critical realism.
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If critical realism is correct, then representationalism would have to be a correct theory of perception.
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quote
saying
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Anti-realism Critical realism (philosophy of the social sciences)
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Subtle realism