Date selection or zi ri xue, Chinese 擇日學 zé rì xué, literally “study of selecting a day”: date selection is provable since the Han Dynasty (206 B. C. to A. D.) where it mainly has been usedd for strategic purposes, later also for economic and personal acitivities like sowing, harvest, marriages and burials.
The time consists of specific changing energy patterns. Date selction tries to find a good timing for certain endeavours and events (which equally have energy patterns) benefiting this action or at least being not unfavorable.
The knowledge of the quality of certain dates has been derived from longterm empirical observation of nature and the sky by scholar interrelating with events on earth to detect patterns therein.
In date selection we differentiate between a generalized form (commonly good or bad dates like dsplayed in the popular Tong Shu) and a personalized form (attuned to a specific person and actions and therefore much more precise).
There are numerous technics to determine favorable and unfavorable dates, e. g. the relatively simple method of the 28 constellations (二十八宿 èr shí bā sù) or the system of grandmaster Dong (董公 dōng gōng) right up to more compex calculations like the method of mystical doors (奇門遁甲 qí mén dùn jiă).
Date selection is also used for complementing and in combination with methods of ba zi suanming and feng shui.