IB Philosophy 10.3 Meditations on First Philosophy – René Descartes Key Definitions

A priori knowledge is knowledge that is justified independently of sensory experience, derived through reason alone. Classic examples include mathematical truths such as "2 + 3 = 5" and logical principles.

Associated with Hume, bundle theory holds that the self is not a distinct, unified substance but merely a bundle of perceptions in constant flux. On this account, introspection never reveals a persistent "I" behind our thoughts and experiences, because the self is nothing over and above the succession of mental states themselves.

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.

In Descartes' epistemology, a clear and distinct perception is one in which nothing is hidden from the attending mind (clarity) and the idea is sharply separated from all others (distinctness), serving as his criterion for truth because such a perception cannot be doubted.

Cogito ergo sum ('I think, therefore I am') is the foundational proposition Descartes discovers in Meditation II, which survives even the most radical doubt because the very act of doubting confirms the existence of the doubter as a thinking thing.

The conceivability principle holds that if something is clearly and distinctly conceivable, then it is genuinely metaphysically possible. Descartes uses this principle to argue for substance dualism, reasoning that because he can clearly conceive of his mind existing without his body, the two must be distinct substances capable of existing independently.

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.

Descartes' dream argument is the sceptical hypothesis that there are no reliable signs to distinguish waking experience from dreaming, which calls into question all beliefs based on sensory experience. The argument does not claim we are dreaming but that we cannot prove we are not.

Epistemological foundationalism is the view that knowledge rests on basic, self-justifying beliefs from which all other justified beliefs are derived. Descartes is the paradigm foundationalist, treating the cogito as the indubitable foundation upon which all subsequent knowledge is built.

The evil demon (also called the "malin genie") is a thought experiment introduced by Descartes in which a supremely powerful deceiver is imagined to be constantly manipulating all of one's perceptions and reasoning. It functions as the most radical stage of hyperbolic doubt, demonstrating that even a priori knowledge cannot be assumed beyond challenge.

a Cartesian distinction between the degree of reality a thing possesses in itself (formal reality) and the degree of reality an idea has by virtue of what it represents (objective reality). In the trademark argument, Descartes uses this distinction to argue that the idea of God, which has infinite objective reality, requires a cause with infinite formal reality, pointing to God as the only adequate cause.

Functionalism is a theory of mind holding that mental states are defined by their causal roles rather than by the physical substrate that realises them. According to this theory, what makes something a mental state is the functional role it performs in mediating inputs, outputs, and other mental states, not whether it occurs in neurons or silicon.

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.

Innate ideas are concepts or principles held to be present in the mind from birth, prior to any sensory experience. Descartes argued that ideas such as God, infinity, and mathematical truths are implanted in us by a non-deceiving God and accessible through the natural light of reason alone, a doctrine standing in direct opposition to the empiricist claim that all ideas originate from experience.

The method of doubt is a systematic philosophical procedure developed by Descartes in which all beliefs that can possibly be doubted are provisionally rejected. The aim is not genuine scepticism but to use doubt as a controlled tool for identifying beliefs that are absolutely certain and can serve as an unshakeable foundation for knowledge.

Natural theology is the attempt to establish truths about God's existence and attributes through reason and observation of the natural world, without relying on divine revelation or scripture.

The ontological argument is an a priori proof for the existence of God that proceeds from the concept of God alone, without relying on empirical observation. Descartes' version in Meditation V argues that because God possesses all perfections and existence is a perfection, God necessarily exists.

Physicalism is the metaphysical position that everything that exists is physical or depends entirely on the physical. Applied to the mind-body problem, it holds that mental states are identical to, or wholly determined by, brain states, encompassing both the identity theory (mental states just are neural states) and eliminative materialism (folk psychology will eventually be replaced by neuroscience).

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.

Property dualism holds that while there is only one kind of substance (physical), conscious experience involves non-physical properties that cannot be reduced to or fully explained in physical terms. David Chalmers defends this position through the hard problem of consciousness, arguing that subjective experience resists any purely physical explanation.

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.

Latin for "thinking thing" or "thinking substance"; Descartes' term for the self or mind, defined as a substance whose entire essence consists in thinking. A res cogitans requires no physical body for its existence and is known with greater certainty than any material object.

Latin for "extended thing" or "extended substance"; Descartes' term for the material, physical world, defined as substance that occupies space and has spatial dimensions. Res extensa is contrasted with res cogitans: the body and all physical objects belong to extended substance, while the mind does not.

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.