《易》「先甲後甲、先庚後庚」說

On ''Three Days before (the turning-point), and those (to be done) Three Days after it'' and ''Three Days before Making any Changes, {Let Him Give Notice of Them); and Three Days after, (Let Him Reconsider Them)'' of the Book of Changes

蠱卦之卦辭「先甲三日，後甲三日」，及巽卦之九五「先庚三日，後庚三日」，歷來頗稱費解，而莫衷一是也。原夫「甲」、「庚」者，當是紀日之名之天干，並非創制命令與變更法令，而「先、後三日」，則乃前後幾天之意，絕非甲日之前、後三天之「辛」與「丁」，與庚日之前、後三天之「丁」與「癸」耳。