Terminus post quem
Terminus post quem and
terminus ante quem specify the known limits of dating for events. A
terminus post quem is the earliest time the event may have happened, and a
terminus ante quem is the latest. An event may well have both a
terminus post quem and a
terminus ante quem, in which case the limits of the possible range of dates are known at both ends, but many events have just one or the other. Similarly,
terminus ad quem is the latest possible date of a non-punctual event, while
terminus a quo is the earliest. Both
terminus post quem and
terminus ante quem are relative dating methods, and cannot provide an absolute date when an event occurred. For example, consider an archaeological find of a burial that contains coins dating to 1588, 1595 and others less securely dated to 1590-1625. The
terminus post quem for the burial would be the latest date established with certainty: in this case, 1595, based on the latest securely dated coin- the burial had to occur in 1595 or later. A secure dating of a younger coin to a later date would shift the
terminus post quem.