An interesting passage in Kant, both because it reminds one of Pascal, and because it clarifies a great deal what Kant sees himself as doing:
The usual touchstone as to whether something asserted by someone is mere persuasion, or at least subjective conviction--i.e., firm belief--is betting. Often someone pronounces his propositions with such confident and intractable defiance that he seems to ahve entirely shed all worry about error. A bet startles him. Soemtimes the persuasion whihc he owns turns out to be sufficient to be asssessed at one ducat, but not at ten. For although he may indeed risk the first ducat, at tend ducats he first becomes aware of what he previously failed to notice, viz., that he might possibly have erred after all. If we conceive in our thougths thte possibility of betting our whole life's happiness on something, then our triumphant judgment dwindles very much indeed; we then become extremely timid and thus discover for the first time that our belief does not reach this far. thus pragmatic belief has merely a degree, which according to the difference of teh interest involved may be large but may also be small.
Even if we cannot undertake anything at all concerning an object, and the assent regarding it is therefore merely theoretical, we can still in many cases conceive and imagine an undertaking for which we suppose ourselves to have sufficient basis if there were a means of establishing the certainty of the matter. And thus there is in merely theoretical judgments an analogue of practical judgments, and for an assent to such judgments the word faith is appropriate. We may call this a doctrinal faith. I would indeed bet all that I own--if this matter could be established through some experience--that there are inhabitants on at least one of the planets that we see. Hence I say that this view--that there are inhabitants also on other worlds--is not mere opinion but strong faith (on whose correctness I would surely risk many of life's advantages.
Critique of Pure Reason, A825/B853; Werner Pluhar, tr. (This is from the Hackett abridged edition, which is easier to lug around.) Kant then goes on to discuss how this relates to questions like God's existence and the future life. On the inhabitants of other worlds things, not only was Kant certain that they exist, but the third part of the Universal Natural History, if I recall correctly, is devoted to laying down precisely what the inhabitants of Saturn must be like.
