Cardinals and ordinals
Cardinal numbers say how many: one, two, three. Ordinal numbers say which position in a sequence: first, second, third. In English the pattern for most ordinals is simple. Take the cardinal and add “-th”: fourth, sixth, seventh, tenth. The first three break the pattern completely, and a few later ones have small spelling changes.
The question is why. The answer is that the first two ordinals come from different words altogether, and the third comes from the cardinal with a sound change.
Why “first” is not “oneth”
“First” is not built from “one”. It comes from an Old English word, “fyrst”, which is related to the word “fore” and to the idea of being at the front. It is historically a superlative form meaning something like “foremost”, the same way “best” is a superlative. A thing that comes first is the one that is at the front of the line. Many related Germanic languages did the same: German has “erste”, Dutch has “eerste”, and these are unrelated to their words for “one” (“eins”, “een”).
Latin did something similar. The Latin ordinal is “primus”, which is related to “prior” and “pro” and again has a sense of “foremost”. English borrowed from this root in words such as “prime”, “primary” and “primitive”. The pattern is widespread: in many languages, “first” is felt to be a different kind of word from “one”, because being at the front is a different idea from being a single unit. That is a reasonable explanation, and the etymologies are well established, although the reason that it happens in so many languages is a matter of interpretation.
Why “second” is borrowed
Old English had a native word for the second item: “other”, which survives in expressions like “every other day”, meaning every second day. When English wanted a more specific ordinal, it borrowed “second” from Old French, which got it from Latin “secundus”. The Latin word comes from the verb “sequi”, meaning “to follow”, so “second” originally meant “following”, the one that comes after the first.
This also explains why “second” is not “twoth”. There was no need to build an ordinal from “two” when the idea of “the next one” already had a word. In French, a distinction survives: “deuxieme” is usually used when there are more than two items, while “second” is traditionally used when there are exactly two. It is a nice survival of an older distinction, though modern French speakers do not always keep it.
Why “third” is slightly odd
“Third” is closer to regular. Old English had “thridda”, built from the cardinal “thri”, the ancestor of “three”. The “r” and the vowel switched places over time, a common sound change called metathesis, so the old form is closer to “three” than the modern “third” suggests. Compare German “dritte” and “drei”, which keep a similar relationship.
From four onward, the ordinal is the cardinal plus a “-th” ending, whose ancestor in Old English was a suffix attached to number words. That ending is the same one in “tenth” and “twentieth”, where it joins the “-ty” ending of the tens as “-tieth”. Some forms have small spelling and sound adjustments. “Fifth” and “twelfth” replace the “v” of “five” and “twelve” with “f”, “ninth” drops the “e” of “nine”, and “eighth” shares its “t” with “eight”. The underlying structure is still cardinal plus ending, and the unusual cardinals eleven and twelve follow the same -th rule.
Ordinals in other languages
Different languages build ordinals differently, and the patterns tell a story about how each language developed.
- Latin used separate forms for the first several: primus, secundus, tertius, quartus, quintus, and so on, which are ancestors of the Romance forms.
- Spanish and Italian keep these roots, as in “primero”, “segundo” and “tercero”.
- German “erste”, “zweite”, “dritte” and “vierte” resemble English in having an irregular first, followed by cardinals plus a suffix.
- Chinese and Japanese, by contrast, use a single marker in front of the cardinal (“di” in Chinese and “dai” in Japanese), so that the second is “di er”, literally something like “number two”. There is no irregular first or second at all, which is one reason that learners often find the system easy.
A look across languages shows that irregular ordinals are especially common for the lowest numbers. That fits a general pattern in language: the most frequently used words are the most likely to keep unusual, ancient forms.
The “second” on the clock
The unit of time called a second has the same Latin source, but a different story. Medieval scholars working with the sexagesimal division of the hour and the degree, a legacy of the Mesopotamian sexagesimal system, divided a unit into sixty parts. The first division was called “pars minuta prima”, the “first small part”, which gives us “minute”. The second division was “pars minuta secunda”, the “second small part”, which gives us “second”. So the clock’s second is an ordinal in disguise: it is the second time that something was divided by sixty.
Ordinals in everyday systems
Ordinals appear in places where order matters. Historic kings share a name and take an ordinal marked in Roman numerals, as in “Henry the Eighth”. A pattern in the names of months also records ordinals: September, October, November and December come from the Latin words for seventh, eighth, ninth and tenth. They have the wrong positions in the modern year, since the old Roman calendar began in March, and the names were preserved after the start of the year moved. Written abbreviations such as 1st, 2nd, 3rd and 4th keep the last letters of the spoken word, and many styles of numeral systems have separate conventions for marking position as opposed to quantity.
Mathematicians sometimes extend the series with “zeroth”, used for the item before the first, mainly in counting from zero. It is a recent coinage used in specific technical settings, not part of ordinary speech.
A short summary
Ordinals are a small system with an irregular start. “First” comes from a word meaning foremost, “second” from a Latin word meaning following, and “third” from a worn-down form of the cardinal. From four on, the pattern is regular. The oddities are traces of how people actually talk about order: the front of a line and the thing that follows are older ideas than any count of units.