David Hume argued that personal identity is not a fixed, unchanging entity, but rather a collection of constantly changing mental states and experiences.

The principle of identity states that a thing is identical to itself, and this is considered a fundamental principle of logic.

Numerical identity refers to the relationship between two things that are the same thing, such as the morning star and the evening star, which are both Venus.

The identity theory of mind states that mental states are identical to brain states, which some argue is incompatible with the idea of free will, as brain states are determined by physical laws.

John Locke argued that personal identity is constituted by our memories, and that if our memories were to be transferred to another body, our personal identity would also be transferred.

The ship of Theseus paradox is a thought experiment that raises questions about the nature of identity by asking whether an object that has had all of its parts replaced remains the same object.

Qualitative identity refers to the relationship between two things that share the same essential properties, such as Socrates and other philosophers.

The bundle theory of mind states that the mind is a collection of mental states, which some argue is too simplistic and does not account for the unity of consciousness.

Rene Descartes argued that personal identity is constituted by our consciousness, and that our thoughts and experiences are what make us who we are.

The sorites paradox is a thought experiment that raises questions about the nature of identity by asking at what point a gradual change in an object's properties results in it becoming a different object.

Contingent identity refers to the relationship between two things that are not necessarily the same thing, such as the Eiffel Tower and the city of Paris.

The identity theory of consciousness states that consciousness is identical to brain activity, which some argue is not supported by scientific evidence, as there is no clear way to measure or identify consciousness in the brain.

Gottfried Leibniz argued that personal identity is constituted by our body, and that our physical continuity is what makes us who we are.

The mind-body problem is a philosophical problem that explores the relationship between the mind and the body, and how mental phenomena can interact with physical phenomena.

Necessary identity refers to the relationship between two things that are necessarily the same thing, such as the Earth and the object that revolves around the Sun.