Page "Definition" Paragraph 57

Locke and Mill also argued that we cannot define individuals.

We learn names by connecting an idea with a sound, so that speaker and hearer have the same idea when the same word is used.

This is not possible when no one else is acquainted with the particular thing that has " fallen under our notice ".

Russell offered his theory of descriptions in part as a way of defining a proper name, the definition being given by a definite description that " picks out " exactly one individual.

Saul Kripke pointed to difficulties with this approach, especially in relation to modality, in his book Naming and Necessity.