Just like in English, Latin makes a distinction between cardinal and ordinal numbers. Cardinal numbers are used to count things (1, 2, 3, 4, etc.), while ordinal numbers are used to put things in lists or to rank them (first, second, third, fourth, etc.).
It is especially important to know the first 20 Latin cardinal numbers: knowing them by heart can help you understand how many other cardinal numbers are formed.
Did you notice a pattern to forming the numbers 11-17? Add the word for one, two, three, and so on to the word for ten:
- ūndecim
- duodecim
- tredecim
- quattuordecim
- quīndecim
- sēdecim
- septendecim
Once you get to 18, however, start counting down from twenty:
- duo dē vīgintī (two from twenty)
- un dē vīgintī (two from twenty)
- vīgintī
The numbers one, two, and three decline like other nouns, but of all the other cardinal numbers (with a few exceptions seen in very high numbers) do not decline.
- ūnus puer, ūna puella, ūnum crustulum
- duo puerī, duae puellae, duo crustula
- trēs puerī, trēs puellae, tria crustula
- quattuor puerī, quattuor puellae, quattuor crustula
- quīnque puerī, quīnque puellae, quīnque crustula
Ordinal numbers are used to put things in an order or rank.
- 1st, 2nd, 3rd, 10th, 50th, et cētera.
- 1st. prīmus, a, um
- 2nd secundus or alter
- 3rd tertius
- 4th quārtus
- 5th quīntus
- 6th sextus
- 7th septimus
- 8th octāvus
- 9th nōnus
- 10th decimus
- 11th ūndecimus
- 12th duodecimus
- 13th tertius decimus or decimus et tertius
- 14th quārtus decimus or decimus et quārtus
- 15th quīntus decimus or decimus et quīntus
- 16th sextus decimus or decimus et sextus
- 17th septimus decimus or decimus et septimus
- 18th duodēvīce(n)simus or octāvus decimus
- 19th undēvīcē(n)simus or nōnus decimus
- 20th vīcē(n)simus
All ordinal numbers decline like normal adjectives and agree with the nouns they describe.
- liber prīmus, pāgina prīma, exercitium prīmum
- liber quīntus, pāgina quīnta, exercitium quīntum