Full Idea
We can only establish that a concept is free from contradiction by first producing something that falls under it.
Gist of Idea
We can show that a concept is consistent by producing something which falls under it
Source
Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884], §095), quoted by Michael Potter - The Rise of Analytic Philosophy 1879-1930 19 'Exist'
Book Reference
Potter,Michael: 'The Rise of Anaytic Philosophy 1879-1930' [Routledge 2020], p.129
A Reaction
Potter quotes this as an example of proof by modelling. If it has one model then it must be consistent. Then we ask whether all the models are or are not consistent with one another. Circular squares fail the test.