Stupid Question ™
March 29, 2001
By John Ruch
Q: Why do most clocks with Roman numerals use “IIII” to represent 4, even though we all learned in school that it’s supposed to be “IV”?
A: That “IV” we learned in school is a medieval invention. The wide usage of IV postdates the invention of the dial-faced clock, which in its earliest forms always used the original Roman numeral IIII for 4.
The Romans had seven basic numerals: I for 1, V for 5, X for 10, L for 50, C for 100, D for 500 and M for 1,000. To signify a number, the proper signs were arranged in descending order of value and simply added up. Thus, 40 was XXXX; 4 was IIII. A few oddball cases aside, Roman numerals were based exclusively on this “additive principle.”
Halfway through the Middle Ages, Roman numerals were still being used and were increasingly considered awkward. To shorten them, a “subtractive principle” was introduced: placing a small-value numeral in front of a larger-value numeral meant the numbers were subtracted rather than added. Thus, 40 was XL; 4 was IV.
This subtractive principle was introduced in the 1200s, but in the case of IV took another couple hundred years to become widely used. It also competed with a variety of other methods, including one in which 4 was written as iiij.
Meanwhile, the sundial with hours marked in Roman numerals had already long been in use. All such sundials used the one-and-only Roman IIII for 4 o’clock. Sundials directly inspired the design of the first dial-faced clocks in the 1300s, which naturally used IIII as well.
The persistence of IIII on clock faces in the post-IV world is fundamentally a matter of tradition. (Indeed, you can find 24-hour clocks in Europe that use IIII for 4, but XIV for 14 and XXIV for 24.) Clockmakers have reinforced it with a body of wild folklore.
Some attribute IIII to various kingly decrees; to Romans finding IV blasphemous as the first two letters of “Jupiter”; or to the most efficient way of casting iron numerals. Some simply think IIII nicely balances the VIII (8) on the opposing side of the clock face.
Nonetheless, isolated uses of IV are known from as early as the 1480s. After 1700, IV became more common, especially in the US and England (where it appears on the Parliament clock tower housing Big Ben). But it remains a minority.
All of this raises the interesting question of why 9 has always been written in the subtractive form IX (rather than the original Roman VIIII). It’s IX on some of the earliest surviving European sundials and clocks on to the present day without variation.
We can only presume that IX was more rapidly accepted than IV—in time to earn its place on the clock face.