The classification turns on two questions: Is the quality actually established? If it is, is an ordinary cause apparent? Together with the nature of an unestablished quality, these yield four modes.
ModeStatus of qualityAttribution1Established; no obvious customary causeA delicate imagined cause2Established; apparent ordinary causeAnother cause replaces it3Unestablished; possible in itselfCause imagined to establish it4Unestablished; impossible in itselfCause imagined for the impossible scenario