Full Idea
Dedekind had an interesting proof of the Axiom of Infinity. He held that I have an a priori grasp of the idea of my self, and that every idea I can form the idea of that idea. Hence there are infinitely many objects available to me a priori.
Gist of Idea
We have the idea of self, and an idea of that idea, and so on, so infinite ideas are available
Source
report of Richard Dedekind (Nature and Meaning of Numbers [1888], no. 66) by Michael Potter - The Rise of Analytic Philosophy 1879-1930 12 'Numb'
Book Reference
Potter,Michael: 'The Rise of Anaytic Philosophy 1879-1930' [Routledge 2020], p.83
A Reaction
Who said that Descartes' Cogito was of no use? Frege endorsed this, as long as the ideas are objective and not subjective.