IB Philosophy 10.3.2 Cogito Ergo Sum: the Self as a Thinking Thing Key Definitions

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.

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.

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.