The faculty of reason.

Agreeableness to reason; that state or quality of a thing which reason supports or justifies; as the reasonableness of our wishes, demands or expectations. The reasonableness and excellency of — charity.

Conformity to rational principles. The whole frame and contexture of a watch carries in it a reasonableness - the passive impression of the reason or intellectual idea that was in the artist.

Moderation; as the reasonableness of a demand.