I Ching/Modified 3-coin Method

Coins Three-coin method

The three-coin method came into use over a thousand years after the yarrow-stalk method. The quickest, easiest, and most popular method by far, it has largely supplanted yarrow stalks, but produces outcomes with different likelihoods. Three coins are tossed at once; each coin is given a value of 2 or 3, depending upon whether it is heads or tails, respectively. Six such tosses make the hexagram. Some fortune-tellers use an empty tortoise shell to shake the coins in before throwing them on a dish or plate.

Modified Three-coin method

The three-coin method can be modified to have the same probabilities as the yarrow-stalk method by having one of the coins be of a second coin type, or in some way be marked as special (i.e., be distinguishable from the other coins). All three coins are tossed at once. The results are counted just as in the original three-coin method, with two exceptions: one to make yin less likely to move, and one to make yang more likely to move. (The probability for 6/8/9/7 in the coin method is 2/6/2/6, but in the yarrow-stalk method is 1/7/3/5; hence, 6 has to occur less often, and 9 has to occur more often.)

In the case where the special coin is tails and the other two are both tails—which would normally produce a 6—re-flip the marked coin: if it remains tails, then it remains a 6 (moving yin); otherwise, treat it as an 8 (static yin). As a 6 can become a 6 or an 8, it reduces the probability of the moving 6. In other words, it makes the old yin less likely to change (or move).

In the case where the special coin is heads and the other two are both tails—which would normally produce a 7—re-flip the marked coin: if it remains heads, then it remains as a 7 (static yang); otherwise, it becomes a 9 (moving yang). As a 7 can become a 7 or an 9, it reduces the probability of the static 7. In other words, it makes the young yang less likely and hence more yangs change as a result.

This method retains the 50% chance of yin:yang, but changes the ratio of moving yin to static yin from 1:3 to 1:7; likewise, it changes the ratio of moving yang to static yang from 1:3 to 3:5, which is the same probabilities as the yarrow-stalk method.