Since the time of the Song dynasty in China, many scholars have attempted to explain the order of the 12 zodiac signs.
The 12 zodiac signs are a part of the traditional culture of many Asian countries. In China, the concept of the zodiac was formed during the Qin dynasty and solidified during the Han dynasty with the animals arranged in the following order: Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig, and has remained unchanged until now.
This order has puzzled many people. Why arrange them in this way? Did the ancients do it arbitrarily or intentionally?
Hypothesis 1: Arranged according to habitual living rules
Many find the order of the 12 zodiac signs very unreasonable, such as the author Wang Huu Quang of 'Ngô Hạ Ngạn Liên' from the Qing dynasty, who once expressed the viewpoint:
'The pig ranks last, the dragon nearly so, the mouse ranks first, who's impressed? The dragon is a divine being, the tiger is mighty, symbolizing the winds and clouds, yet it stands in the middle, although above the pig, it still endures standing beneath the mouse, isn't that contradictory!' (rough translation).
We all know that the 12 zodiac signs correspond to the 12 earthly branches, namely Rat-Mouse, Ox-Buffalo, Tiger, Rabbit (in Vietnam, Cat), Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig.
The 12 earthly branches represent 12 months and 12 two-hour periods (1 two-hour period corresponds to 2 hours today). Based on this, people rely on the habitual activities of the 12 zodiac signs to explain their order.

As the scholar during the Southern Song Dynasty, Ly Truong Khanh, said in his book 'Tùng Hà quán chuế ngôn':
The Rat hour (11 pm-1 am) is when rats are most active, hence associating the Rat with this hour.
The Buffalo hour (1 am-3 am), the buffalo is still chewing its food, preparing to plow early in the morning.
During the Tiger hour (3 am-5 am), the tiger is hunting for food in the forest, most ferocious during this time.
During the Rabbit hour (5 am-7 am), the sun hasn't risen yet, the moon (yin) still shines, the jade rabbit is grinding herbs.
During the Dragon hour (7 am-9 am), the dragon is making rain.
During the Snake hour (9 am-11 am), the snake is coiling up in its den.
During the Horse hour (11 am-1 pm), the sun is high, the roads are filled with galloping horses.
During the Goat hour (1 pm-3 pm), the goat is grazing.
During the Monkey hour (3 pm-5 pm), monkeys are frolicking around the forest.
During the Rooster hour (5 pm-7 pm), chickens return to their coop.
During the Dog hour (7 pm-9 pm), dogs remain vigilant guarding the house.
During the Pig hour (9 pm-11 pm), pigs are fast asleep.
However, while this explanation is intriguing, it lacks accuracy. Considering habits, roosters usually crow in the morning, so they correspond to the Rabbit hour, not suitable for the Rooster hour.
Hypothesis 2: Arranged according to the principle of yin and yang.
The 12 earthly branches are divided into yin and yang: Rat, Tiger, Dragon, Horse, Monkey, Dog belong to yang; Ox, Rabbit, Snake, Goat, Rooster, Pig belong to yin. Accordingly, yang ranks odd, yin ranks even.

A very interesting discovery is that the number of claws of the 12 zodiac signs also follows the odd-even counting of yin and yang.
The first person to make this observation was Hong Ton, a member of the Song dynasty. In his book 'Duong Coc man luc', he classified the zodiac signs into two categories of yin and yang: Rat, Tiger, Dragon, Monkey, Dog have 5 claws and Horse has 1 hoof, belonging to the odd group. Ox, Rabbit, Goat, Rooster, Pig all have 4 claws, belonging to the even group.
The remaining are the Rat and the Snake. The Snake has no legs but its tongue splits into two parts, so it is classified as even. The case of the Rat is the most special: The front legs of the Rat have 4 toes (even), the hind legs have 5 toes (odd). The Rat is associated with the Rat hour from 11 pm the previous night (yin) to 1 am the next morning (yang). Therefore, the Rat is associated with the Rat hour and ranks first among the 12 zodiac signs.
Hypothesis 3: Based on folklore legend.
Chinese folklore passes down a story about the origin of the 12 zodiac signs as follows:

The Jade Emperor selected 12 animals to represent each year. On the day of the ceremony to determine their positions in the zodiac, the Jade Emperor said: 'The Ox is the largest, so I shall place the Ox at the head.' The Mouse objected, claiming that humans considered it to be even larger and more magnificent than the Ox.
To prove the Mouse's words, the Jade Emperor and all the animals descended to earth to inquire. When the Ox passed by a human, they only heard the person say 'This Ox is truly fat and strong', without mentioning its size.
At this moment, the Mouse jumped onto the Ox's back, standing upright on its hind legs, and the human immediately exclaimed in horror: 'This mouse is too big!'. Thus, the Mouse was chosen by the Jade Emperor to stand at the head of the 12 zodiac signs.

In folk legends, the Mouse is known as a cunning and crafty creature. It used its wits to claim the first position among the 12 zodiac signs.
In ancient times, agriculture was the main livelihood, and fields infested with mice were devastated, houses with mice were damaged, and even rice and wheat were eaten clean by them. But catching or exterminating mice was not easy as they were very cunning, so they were not favored. Therefore, ancient Chinese believed that the Mouse, being the smartest, should be ranked first among the 12 zodiac signs.
Source: Toutiao, 163
