Full Idea
The logicism of Frege, Russell, Whitehead, Church and Carnap condones the use of bound variables or reference to abstract entities known and unknown, specifiable and unspecifiable, indiscriminately.
Gist of Idea
Logicists cheerfully accept reference to bound variables and all sorts of abstract entities
Source
Willard Quine (On What There Is [1948], p.14)
Book Reference
Quine,Willard: 'From a Logical Point of View' [Harper and Row 1963], p.14