What are moon blocks?

The blocks are called jiaobei (筊杯) in Mandarin and poe in Hokkien, which is why English writers sometimes speak of poe divination. They are usually carved from wood or bamboo. Each piece has one flat side, called the yang side, and one rounded side, called the yin side.

A 19th-century pair from China in the Penn Museum shows the classic form: thick wooden crescents, beveled along the inside curve. The museum's catalogue says priests used them in front of temples and that the position in which they landed was read as an omen.

Moon blocks are found at temples and home shrines in China, Taiwan and elsewhere. They may be used alone, for a single question, or alongside fortune sticks, to check whether a stick drawn is the right one.

Accounts of practice in Taiwan describe a person kneeling, stating their name, birth date and address, asking the question, and letting the blocks drop to the floor. Some people first pass the blocks three times around the incense burner.

Three results are usual. One flat side and one round side up is the sacred throw (聖筊), read as yes. Two flat sides up is the laughing throw (笑筊), read as undecided, and the question is usually asked again. Two round sides up is the yin throw (陰筊), sometimes called the angry throw (怒筊), read as no.

Rarely, a block stands on its edge (立筊). This falls outside the three results, and people give it a range of meanings. For important matters some people ask for three sacred throws in a row, while others accept one.

A clear literary witness comes from the Tang dynasty poet Han Yu (768 to 824). In a poem on visiting the shrine of Mount Heng, he describes the shrine keeper taking up the blocks and showing him how to throw them, in the line 手持杯珓導我擲. A modern annotator of the poem glosses his word, 杯珓, as a crescent-shaped object used for divination.

Later evidence is sparse in the places we could read. The Penn Museum pair, a gift from the Friends Historical Library at Swarthmore in 1967, is dated only to the 19th century.

Modern study has focused on how people use the blocks now. Wu Pin-Ta, writing in a journal of National Chengchi University in 2014, examined standing blocks in fifty Taiwanese temples between 2008 and 2013. He treats tossing as a way believers seek a god's guidance on decisions they find hard to settle, and looks at the varied meanings given to a result that fits neither yin nor yang.

We did not find a dated account of how or when moon blocks began. Reference works say only that they come from China. Han Yu shows they were known in his day, and he does not say how old they were.

A Song book, Cheng Dachang's Yanfanlu (演繁露), says in its entry 卜教 that two clamshells were thrown to the ground, and that later people also used bamboo or wood cut to that shape. Cheng wrote long after Han Yu, so this does not date the origin. Clamshells are reported as a substitute in some places.

Sources disagree on the names. One encyclopedia article gives two flat sides as the angry answer and two round sides as the laughing answer. Other accounts, and this site, give the reverse. Temples also differ on how many sacred throws are needed and how a laughing or yin throw should be treated, so the custom of the place you are in is the one to follow.