Full Idea
For some purposes the variables of first-order logic can be regarded as prepositions and place-holders that could in principle be dispensed with, say by a system of arrows indicating what places fall in the scope of which quantifier.
Gist of Idea
Perhaps variables could be dispensed with, by arrows joining places in the scope of quantifiers
Source
Ian Hacking (What is Logic? [1979], §11)
Book Reference
'A Philosophical Companion to First-Order Logic', ed/tr. Hughes,R.I.G. [Hackett 1993], p.242
A Reaction
I tend to think of variables as either pronouns, or as definite descriptions, or as temporary names, but not as prepositions. Must address this new idea...