A terminus post quem is the earliest date the event may have happened or the item was in existence, 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, a terminus ad quem 'limit to which' is the latest possible date of a non-punctual event (period, era, etc.), whereas a terminus a quo 'limit from which' is the earliest. The concepts are similar to those of upper and lower bounds in mathematics.
These terms are often used in archaeological and historical studies, such as dating layers in excavated sites, coins, historical events, authors, inscriptions or texts where the exact dates may not be known or may be in dispute.[2][3]
Related terms[edit]
A terminus ante quem non differs from a terminus post quem by not implying the event necessarily took place. 'Event E happened after time T' implies E occurred, whereas 'event E did not happen before time T' leaves open the possibility that E never occurred at all.
In project planning, sometimes the phrases "no earlier than" / "no later than" (NET/NLT) are used.