A conscience which, after due diligence, is certain that its judgment is the correct one is a certain conscience. The certainty required is a not an absolute certainty, but a moral certainty—that which a reasonable person would judge to be correct, without a prudent fear of being wrong.
Moral certainty is the standard required in both morality and law. We should not be afraid to act on a moral certainty; we do it all the time! For example, we drive to work without an absolute certainty we won’t kill, or be killed, along the way. Rather, we have a moral certainty that IF we drive lawfully, and show reasonable care, we and those with whom we share the road will arrive safely at our destinations.