 The Logic ends in a way befitting a treatise associated with the Port-Royal abbey. The last four chapters consider how to fit into the method the deliverances of knowledge derived from authority instead of from reason. Knowledge from authority is of two kinds: knowledge from God, which is called faith, and knowledge from humans “worthy of credence”, which is called belief or opinion (IV.12, 260). God’s deliverances are infallible, but human authorities differ in their reliability. The best opinions come from the constant testimony of many sources. These can reach moral certainty, i.e., all the certainty that is required for practical purposes. Faith and opinion are, however, underwritten by reason because, according to the authors, reason reveals that God is infallible and that skepticism about reliable human authority is groundless.