The texts known to Anglo-Saxon studies as ‘prognostics’ comprise, by scholarly consensus, approximately forty to fifty items of various lengths in Latin and Old English. They are a diverse and somewhat loosely defined group, including such things as predictions based on the day of the week on which something occurs, predictions based on natural phenomena such as thunder or wind, lists of lucky and unlucky days in the year (sometimes called ‘Egyptian’ days), lunaria or calendars for the lunar month listing good and bad days for illness, bloodletting, childbirth, or the interpretation of dreams, alphabetical lists giving the meaning of objects seen in dreams (the Somniale Danielis), and numerological devices for predicting the outcome of an illness. Prognostics differ from most later systems used to obtain knowledge of future events in the fact that they are calendrical rather than astrological—that is, their predictions are derived not by calculating the positions and influences of the stars and planets but by observing the cycles of days, months, and years.

While prognostication or prediction appears to be a universal human activity found in virtually all cultures, surviving Anglo-Saxon texts labeled ‘prognostics’ derive from continental Latin sources rather than native Germanic traditions; they are in that sense works of science and learning rather than folklore or popular belief. It is generally thought that prognostics originated in a late-classical Hellenistic milieu; most of the texts represented in T are found in Greek versions, but since these versions are often later than the earliest surviving Latin copies, one can only presume that the texts were translated from Greek into Latin and not vice versa.