摘要
學易經的人大概都有這樣的看法，伏羲排了先天八卦，周文王排了後天八卦，先天八卦為體，後天八卦為用。如果我們將先天八卦置於九宮格中（見圖一），北（N）為坤，南（S）為乾，東（E）為離，西（W）為坎（注意：中國古代繪方位圖是南上北下，和現代北上南下的習慣不同）；若將後天八卦置於九宮格中（見圖二），北為坎，南為離，東為震，西為兌。另外，古人亦曾把八卦擬人化當做一家八口，分別用不同的卦來代表：乾（符號略）為父，坤（符號略）為母，長男為震（符號略），中男為坎（符號略），少男為民（符號略），長女為其（符號略），中女為離（符號略）,少女為兌（符號略）。我們想像一種情況，有一家庭恰巧有九間房有如九宮格，除了中間房不住人外，一家八口每個成員都可分配到一間房，如按照圖一的先天八卦讓成員分別進駐，則可看到母住北邊房，父住南邊房，如圖六。當孩子們逐漸長大，於是住房若能做適當的調整會更方便些，此時若按圖二後天八卦去調整會得到的結果如圖七。本文除了提供上述現象的詮釋外，也將用幾何圖解展現從先天轉換成後天之路徑圈，另外還有如「乾」在先天住一號房封在後天住六號房，「坤」在先天住八號房封在後天住二號房等，這房號分配於先天、後天八卦依之順序規則為何，若能以「卦與方位」及「方位與順序」的數學函數來呈現，可以更清楚地表達出來。
並列摘要
In learning I-Ching, most of people share the same opinions that primitive eight trigram was arranged by Fuxi and posterior eight diagrams by King Wen of Zhou state; the former was regarded as body and the latter as function. When we put the Primitive Eight Trigram in the nine-square grid (see figure 1), hexagram Kun will be seen in north (N), Qian in south (S), Li in east (E), and Kan in west (W) (Note: the ancient orientation drawing is up and down for south and north, contrary to the modern one with up and down for north and south). But when we put Posterior Eight Diagrams in nine-square grid (see figure 2), then hexagram Kan will be seen in north (N), Li in south (S), Zhen in east (E), and Dui in west (W). Furthermore, the ancient people had ever taken the eight diagrams as a family, in which Qian stands for father, Kan for mother, Zhen for the eldest son, Kun for the middle son, Xun for the youngest son, Gen for the eldest daughter, Li for the middle daughter and the Dui for the youngest daughter. We can image a situation that a family has a house with nine rooms, each of which is paired with a family member except the central room for none. Accordingly we see in figure 1 that the family members are placed in eight diagrams with mother staying in the northern room, father in southern room (see figure 6). When children all grow up, we may have the room accommodation made properly in light of Posterior Eight Diagrams and will get the result as illustrated in figure 7. In addition to the interpretation of the above-stated phenomena, the paper also unfolds the path of Primitive Eight Trigram transforming into Posterior Eight Diagrams by using geometric figures: for example, hexagram Kan lives in the first room in Primitive Eight Trigram but in the sixth room in Posterior Eight Diagrams; hexagram Kun in the eighth Room in Primitive Eight Trigram but in the second room in Posterior Eight Diagrams. How the sequence of the room number is organized in Primitive Eight Trigram and in Posterior Eight Diagrams respectively can be expressed in a more clear way through the presentation of mathematical function of ”diagrams and orientation” and ”orientation and sequence”.