How Latin numbers work

Latin is famous for its endings, and its numbers are where it quietly lets you off. Most of them never change. The whole grammar of Latin counting is three small words that decline, a subtraction at eighteen and nineteen, and one noun, milia, that wants a genitive after it.

One to ten: three that decline, the rest that never do

There is no zero. Classical Latin had no number word for nothing; a Roman said nullus (no, not any) or nihil (nothing): Nihil habeo. - I have nothing.

12345678910

1. 1unus
2. 2duo
3. 3tres
4. 4quattuor
5. 5quinque
6. 6sex
7. 7septem
8. 8octo
9. 9novem
10. 10decem

Count the apples from unus to decem. Only the first three change to agree with what they count.

The first three agree with what they count in case and gender. From four on, the number is indeclinable, and the noun carries the case on its own:

• duae partes - two parts (pars is feminine)
• quattuor partes - four parts
• cum quattuor partibus - with four parts

The teens, and why eighteen counts backwards

Eleven to seventeen are a unit fused onto ten, with some wear at the join:

Then Latin changes direction. Eighteen is two-from-twenty and nineteen is one-from-twenty, and the de in the middle is the preposition from:

The pattern runs at the top of every ten:

Decem et octo, ten and eight, does turn up for eighteen (the Vulgate uses it), but the subtractive forms are the classical norm.

The tens and a hundred

All indeclinable. Watch the vowel before -ginta: septuaginta has a u, octoginta an o, and nonaginta starts like nonus (ninth) rather than novem. English kept one of them: the Greek Old Testament is the Septuagint, after the seventy translators of the legend (the story actually has seventy-two, rounded down).