IB Philosophy 10.3.6 Knowledge of the External World Key Definitions

The Cartesian Circle is the charge, first raised by Arnauld, that Descartes' reasoning is viciously circular. He uses clear and distinct perception to prove God's existence, then relies on God's existence to guarantee that clear and distinct perceptions are reliable.

Doxastic voluntarism is the view that belief formation is, at least partly, under direct voluntary control, so that a person can choose what to believe in the same way they can choose an action. Descartes implicitly relies on this when he claims we can avoid error by choosing to withhold assent whenever our ideas are not clear and distinct.

Idealism is the metaphysical and epistemological thesis that reality is fundamentally mental or mind-dependent, so that physical objects either reduce to collections of ideas or exist only insofar as they are perceived. Developed by Berkeley and later by Hegel, the view challenges common-sense realism by arguing that we can never step outside experience to verify an independently existing material world.

properties of material objects that are held to exist in those objects independently of any perceiver. For Descartes, the primary qualities are extension, shape, size, motion, and number, which the intellect can grasp clearly and distinctly. They contrast with secondary qualities such as colour, warmth, and taste, which Descartes regards as modes of sensation in the perceiving mind rather than genuine features of external reality.

Rationalism is the epistemological position that reason, rather than sensory experience, is the primary source of genuine knowledge. Rationalists such as Descartes hold that some truths are knowable through pure intellectual insight or a priori reasoning alone, independently of what the senses report.

sensory properties such as colour, sound, taste, smell, and warmth that Descartes and Locke argue do not inhere in external objects but exist only as experiences produced in a perceiving mind. Unlike primary qualities (extension, shape, motion), secondary qualities are mind-dependent responses to the physical micro-structure of matter and tell us less about the objective nature of things than about our own sensory apparatus.

The verification principle is the criterion of meaning proposed by logical positivists stating that a non-tautological statement is meaningful only if empirical observations could count for or against it, rendering metaphysical and theological claims devoid of propositional content.