The art of divination, with a history spanning millennia, has evolved into various methods, reflecting distinct phases of the Book of Changes' development.
Among these, casting lots with three coins was prevalent and simpler. In ancient times, scholars often used coins from their era or ancient coins. Common ancient coin designs mainly differed in era, maintaining a circular shape with a square hole in the center, depicting the reigning dynasty on one side and the coin's value on the other. (see image)
In modern times, contemporary coins are used in most countries, including Vietnam, which has circulated various low-denomination coins, making the divination process easier.
Contemporary coins also feature the national emblem of the issuing country on one side, while the other side bears the coin's denomination.

Positive Side (Heads)
Many mysticism enthusiasts on forums utilize contemporary coins for divination, but the methods of distinguishing positive and negative aspects vary. Some explain that the national emblem represents the issuing country; in Vietnam's emblem, an additional star symbolizing the sky makes it positive. The other side, featuring the denomination and patterns like stilt houses and the One Pillar Pagoda, symbolizing the land, is considered negative.
Others don't base their divination on the positive or negative nature of the coin. Instead, they arbitrarily assign positivity or negativity in each session, leading to inconsistencies and straying from the Yin and Yang principles of the I Ching.
In my view, when using contemporary coins from Vietnam or any other country or region, the first consideration is acknowledging that we are using MONEY for divination. Being currency, the side determining the coin's value and displaying the national emblem is the main side, hence positive or Yang. The other side naturally becomes negative or Yin.

Negative Side (Reverse Side)
This aligns with the Yin and Yang rule of ancient coins. In ancient coins, the side representing the dynasty (e.g., with the words 'Càn Long Thông Bảo') is the negative side (Reverse), a principle upheld in modern coins as well. The side with the national emblem, symbolizing the government issuing the currency, is also the negative side (Reverse).
The other side signifies the coin's value, distinguishing it as MONEY rather than just a piece of metal or zinc. Through this side, we ascertain the coin's denomination, establishing its value, and thus, this side is inherently positive or Yang.
Here is a method for determining the positive and negative aspects of contemporary coins.
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Explanation of the phenomenon of divination using the 'positive and negative coin casting' technique
