“Reiwa” and “the Edo period” both refer to periods of time in Japan, but they are not the same kind of name.
Reiwa is an imperial era name, or gengō. Era names are official names used to date years. Add a number, as in “Reiwa 8,” and you can identify a specific year.
In Japan today, a new era name begins when a new emperor takes the throne. Historically, however, this was not always the system. In earlier periods, an era name could change several times during the reign of a single emperor.
Names such as the Edo period, Heian period, and Kamakura period are different. They are historical period names used to divide the past into useful blocks for understanding Japanese history. “Edo” was not officially announced as an era name, and people did not start counting years from an “Edo 1.”
That is why you would not say “Edo 8” to identify a year.
The difference becomes especially clear when you realize that one historical period can contain many different imperial era names.
During the Edo period, for example, era names such as Keichō, Genna, Kan’ei, Genroku, Kyōhō, and Tenpō were used. “Edo period” is the larger historical category, while the individual era names were used to date years within it.
The boundaries of historical periods are also not always as precise as an official change of era name. Historians may differ over exactly when a period begins or ends, depending on which political or social changes they consider most important.
“Shōwa” can make the distinction a little confusing.
Shōwa is an imperial era name, but people also say “the Shōwa period” when referring to that broader stretch of time. Even so, there is still a clear difference in how the terms are understood: Shōwa is fundamentally an era name; Edo is not.
In simple terms:
An imperial era name is an official name used for dating years.
A historical period name is a label used to organize history into broader periods.
Reiwa and the Edo period both tell you where you are in Japanese time, but they belong to different systems and serve different purposes.
