Full Idea
Quine said a logical truth is a truth in which only logical constants occur essentially, ...but then a fruitful definition of 'logical constant' is called for.
Gist of Idea
If logical truths essentially depend on logical constants, we had better define the latter
Source
comment on Willard Quine (Carnap and Logical Truth [1954]) by Ian Hacking - What is Logic? §02
Book Reference
'A Philosophical Companion to First-Order Logic', ed/tr. Hughes,R.I.G. [Hackett 1993], p.227