Over the years, I’ve written about certain sekku (節句) or seasonal holidays in the traditional Japanese calendar. These are:

1. Girl’s Day : March 3rd (3/3)
2. Children’s Day : May 5th (5/5)
3. Tanabata : July 7th (7/7), and
4. Day of the Chrysanthemum (9/9)

Notice the dates of each holiday: odd-numbered month with matching odd-numbered day. Turns out that there’s a reason for this.

In Chinese Taoist numerology, numbers are divided into “yang” and “yin” numbers: odd numbers are yang (陽) because they are considered unstable and dynamic, while even numbers are stable and static, thus yin (陰). But because yin and yang depend on one another, and change into one another, if you add yang and yang together, you get yin. If you add yin and yin together, you get yang.

Thus, it was thought that dates on the calendar with double-yang numbers (7 and 7, 5 and 5, etc) would become yin and thus were inauspicious. Holidays were developed to counteract the yin effect, and that’s why seasonal holidays were held on double-odd dates.

Taoism is not a major influence in Japanese culture (at least in modern times), but it’s interesting so see how it still influences traditions, especially those from antiquity.

Anyhow, TIL. 😎

P.S. Learned all this from this excellent book. Highly recommend.