Full Idea
Leibniz argued that the necessary truths are just those which can be proved from identities by pure logic in a finite number of steps. ...[232] this claim is vindicated by Gentzen's sequent calculus.
Gist of Idea
Necessary truths are those provable from identities by pure logic in finite steps
Source
report of Gottfried Leibniz (works [1690]) by Ian Hacking - What is Logic? §01
Book Reference
'A Philosophical Companion to First-Order Logic', ed/tr. Hughes,R.I.G. [Hackett 1993], p.226
A Reaction
This seems an odd idea, as if there were no necessary truths other than those for which a proof could be constructed. Sounds like intuitionism.