Opinion (n.) formed outside the field of experience is mere play with thoughts.
Opinion (n.) is too little for the transcendental use of reason, and knowledge too much.
Opinion (n.) is knowledge on the instalment plan: objective but insufficient grounds that can be topped up until they become knowing.
Opinion (n.) needs at least one thing known to tie it to truth; an opinion connected by mere opinion is only a game of the imagination.
Opinion (n.) is possible only about things we could in principle see — the ether, inhabitants of other planets — but an a priori opinion is the straight road to figments of the brain.
Opinion (n.) is absurd in pure mathematics and in morals alike: there one must know or refrain — one may not venture an action on the mere opinion that it is allowed.