1. Why Did the Romans Call Wednesday "Mercury's Day"?
In the Roman system of weekday names, the seven days were tied to seven bright objects that move across the sky: the Sun, the Moon, and five planets you can see without a telescope. In Japan, where this notebook was first written, the weekday names still say so: the word for Wednesday is 水曜日 (suiyōbi), "water day," and the planet Mercury is called "water star." [1]
In the Greek and Latin versions of this system, each day belongs to a planet and its god. Wednesday was hēmera Hermou in Greek, "day of Hermes," and dies Mercurii in Latin, "day of Mercury." [1] The earliest surviving text that names the days after the seven planets is an astrology book by Vettius Valens, written around AD 170. The Latin name for Wednesday is dated to the late second or early third century. "Earliest surviving" only means the earliest we have found, not that nobody did it before. [2]
Today most Romance languages, which grew out of Latin, still carry Mercury: mercredi in French, miércoles in Spanish, mercoledì in Italian. [2] English did not. So what happened on the way north?
2. How Did Mercury Turn Into Woden in English?
When Romans and Germanic peoples came into closer contact, around the first century AD Wikipedia, citing the scholar Rudolf Simek, says the Germanic side began to match Roman gods with gods of their own. This habit is called interpretatio germanica. [3] In this matching, Mercury, whom the Romans linked with travelers and clever speech, was paired with Woden (also called Wōdanaz, Wuotan, and, in Norse myth, Odin). [3] The sources I read do not explain why these two were paired, so I will not guess at the reasons.
Once Woden was "the Germanic Mercury," the day of Mercury could be translated piece by piece into the day of Woden. A word made that way, by copying the pattern of another language's phrase, is called a calque (say "calk"). Old English had wōdnesdæg, "Woden's day," and the other Germanic languages followed the same pattern. The same swap gave us Tuesday (Tiw), Thursday (Thor), and Friday (Frigg). [2] [3]
That swap is why the day belongs to Woden in English, Dutch (woensdag) and Danish (onsdag). [4]
Why is there a "d" in Wednesday that nobody says?
If the word had simply kept its old sound, we would expect to write "Wodnesday." The spelling Wednesday arose later, in Middle English, through changes in spelling and by analogy with other words, not by the sounds passing straight down. [2] So the silent "d" is a small trace of Woden still sitting in the spelling.
3. Which Languages Named Wednesday After a Planet, a God, or Something Else?
Put the names side by side and they fall into groups:
- Planet-god (Mercury): Latin and the Romance languages such as French, Spanish and Italian. [2]
- Germanic god (Woden): English, Dutch, Danish. [4]
- Planet through the Five Elements idea: Japanese "water day," because Mercury is the "water star." [1]
- Position in the week: German Mittwoch, Icelandic miðvikudagur, Finnish keskiviikko, and Russian sreda all mean "middle." [4]
Same day, same position in the week, and four different ideas about what to call it. Unlike the first three groups, the last one contains no god and no planet: its names describe the day's position in the week. How did that happen?
4. Why Does German Say "Midweek" Instead of Naming a God?
German Mittwoch is "mid" plus "week." It goes back to Old High German mittawehha or mittiwehha, found in writing from the 9th century, in texts by writers such as Otfrid and Notker. It copies the Church Latin phrase media hebdomas, "middle of the week." [4] [5]
Before that, the German-speaking lands also had a Woden-day word, Wotanstag. German Wikipedia explains the new name as a way for Christian missionaries to avoid mentioning a pre-Christian god. It also says the same page names Portuguese and Icelandic as cases where the pagan god disappeared from the day's name, and it points to the influence of individual missionaries, with Martin of Braga in the 6th century cited as an example. That is why a Portuguese Wednesday is quarta-feira, "fourth day." [4] Wiktionary agrees that the old Woden word was already displaced in Old High German times. [5]
The "middle" in the name is easy to check. Count Sunday as day one and Wednesday is day four, exactly in the middle of seven. [4] English also has a trace of this idea in the word midweek.
5. What Do We Still Not Know About the Names of Wednesday?
A few things are less certain than the tidy list above makes them look:
- The sources I could read do not explain why Woden was matched with Mercury in particular.
- The missionary explanation for Mittwoch comes from one German encyclopedia article; I did not find a second, independent source that spells out the motive.
- "Earliest surviving" evidence for planet-named days (about AD 170) may not be the true beginning of the habit.
If you read more about this, notice which claims come with a named author or an old text, and which come from summaries. That is how researchers decide what to trust.
6. How Can You Look for the Gods and Planets in Your Own Week?
You can do this with a pen and a dictionary or translation site:
- Write the seven English day names and next to each the French, Spanish or German name (or any language a friend or relative speaks).
- Mark each name as a planet or god, a position ("middle," "second") or something else.
- Look at which days stayed close to the Roman names and which were swapped. Do Wednesday and Thursday follow the same pattern as in the lists above?
Then try the question that these notes cannot answer: why was Woden matched with Mercury? A library book on Old English or Norse myth is a good next step.