The Post Hoc fallacy is the incorrect conclusion that an event that preceeds another event is the cause of the latter. The rooster's crowing need not cause the sun to rise. Normative statements are not subject to objective verification. Efficiency in production means that one is getting the most out of one's resources. It is not possible to increase the production of one good without decreasing the production of some other good.
Inverse relationship are when two variables move in the opposite direction.
A double coincidence of wants is needed for efficient barter trade. Each partner in the trade must be offering what the other wants and each must want what the other is offering.