Tiān Yǐ

天乙 (tiān yǐ) is the third favorable star of the Eight Mansions book 陽宅十書, with the star name 巨門 and the element earth. That older book writes 天乙, and this site follows it. The same seat is also written 天醫, Heavenly Doctor.

The sources show where 天醫 appears, though not where it began. 協紀辨方書 卷二, an imperial almanac, says that the 巨門 of the 大遊年 scheme is also called 天醫, so this seat carried that name in the almanac. The word is also in the marriage-matching list quoted in 協紀辨方書 卷三十六, which ranks 生氣, 天醫 and 福德 as the best group and which the imperial editors dismiss as a forgery by practitioners, falsely credited to 呂才. A house text attributed to 蔣大鴻 also names 天醫, only to set it aside, but we can only paraphrase it because its edition cannot be checked. Our sources do not say how the two names came to share this seat.

In the 大遊年 scheme 天乙 pairs 乾 with 艮, 坎 with 震, 巽 with 離 and 坤 with 兌, each pair within one group of four, by our reading of the verses. The book's later method of 元空裝卦 does not use this star at all, because its pairs would put yang beside yang or yin beside yin. 巨門 is also the name of the second of the nine stars.