n. (Logic) 1a. an expression capable of having a unique reference; for example, `the woman in white' or `Rosemary's baby'.
b. an analogous plural expression; for example, `the dogs of war'. 2. theory of definite descriptions. the analysis, proposed by Bertrand Russell, of singular definite descriptions in which a sentence of the form the F is G is said to be equivalent to
there is one and only one F and it is G,
which is abbreviated G[(ι x)Fx]. This can be defined in terms of the unique quantifier as
G[(ι x)Fx] ≡ (∃!x)Fx & (∀x)(Fx → Gx)
or in terms of the existential quantifier as
G[(ι x)Fx] ≡ (∃x)((Fx & (∀y)(Fy → x = y)) & Gx).