Full Idea
It is an anacoluthon to say that a proposition is impossible because it is self-contradictory. It rather is thought so to appear self-contradictory because the ideal induction has shown it to be impossible.
Clarification
An 'anacoluthon' changes subject in mid-sentence
Gist of Idea
Self-contradiction doesn't reveal impossibility; it is inductive impossibility which reveals self-contradiction
Source
Charles Sanders Peirce (The Nature of Mathematics [1898], III)
Book Reference
Peirce,Charles Sanders: 'Philosophical Writings of Peirce', ed/tr. Buchler,Justus [Dover 1940], p.147