Esperanto Numbers and Counting: Nine Roots, Four Suffixes and No Exceptions

Most languages make you pay for numbers twice: once for the words, and again for the irregularities. English wants one, two, three and then first, second, third, which share no shape at all, followed by eleven and twelve hiding the ten they are made of, followed by thirteen suddenly announcing it.

Esperanto charges once.

The whole vocabulary

Nine roots and three sizes:

That is the list. There is no more number vocabulary in the language.

The join rule

Two operations, two spellings.

Multiply, and it joins up. Add, and it stays apart.

Dudek du is therefore both rules working in one breath, and once you have seen it the rest of the number line writes itself. 1987 is mil naŭcent okdek sep, and you can read that off the digits without pausing.

The one wobble is du mil for 2,000, which convention writes as two words even though the multiplication rule points at dumil. Both appear in print. Nobody will misunderstand you either way.

They do not decline

Cardinals take no -j and no -n, ever:

Mi vidas tri librojn.

Libro picks up both endings because it is the object and there is more than one of it. Tri sits there unchanged. If your first language attaches endings to numbers, this is the one habit to break, and it is a pleasant one to break because there is nothing to learn in its place.

Words built from numbers do decline, because they have stopped being numbers. Ordinals are adjectives, so la unuajn tagojn behaves like any other adjective and noun pair. Duono is a noun, so mi prenis duonon takes the accusative like mi prenis panon.

Four suffixes

Here is where the scheme pays for itself. Each suffix attaches to any number, and the result is a real word nobody needed to list in a dictionary.

Ordinals with -a

Unua, dua, tria, kvara, kvina. No new roots, no first and second arriving from nowhere. Compounds take a hyphen so the -a lands on the whole thing: la dek-dua (the twelfth), la dudek-unua (the twenty-first).

Swap the -a for -e and you get the adverb: unue (firstly), due (secondly), trie. Useful the moment you start listing reasons.

Time uses ordinals as English does: la tria horo is three o'clock, and je la tria is at three.

Fractions with -on-

Duono a half, triono a third, kvarono a quarter, dekono a tenth. As an adjective: duona horo, half an hour. As an adverb: duone, halfway.

English has bespoke words for the small fractions and then surrenders to one seventeenth. Dek-sepono needs no surrender.

Multiples with -obl-

Duobla double, triobla triple, dekobla tenfold. The adverb is often the natural one: mi pagis duoble, I paid double. Duobligi is to double something, which is the -ig- suffix doing its usual work.

Collectives with -op-

-op- means in groups of. Ili laboris duope is they worked in twos. Kvarope in fours. La infanoj eniris triope, the children came in threes.

Two more things numbers can become: add a plain -o and you get the group itself, so deko is a set of ten and dekduo is a dozen. That matters for the next section.

da: linking a quantity to its stuff

Da is the preposition that connects a measurement to the thing measured.

iom da akvo - some water

multe da homoj - many people

peco da pano - a piece of bread

kiom da tempo - how much time

amaso da homoj - a crowd of people

Now the bit people get wrong. A bare numeral takes no da. Tri libroj is three books, full stop. Tri da libroj is not Esperanto, because tri is a numeral, not a quantity noun, and there is nothing for da to join.

The moment the number becomes a noun, da returns: dekduo da libroj, a dozen books. Cento da homoj, a hundred of them.

De covers everything else English calls of - possession, origin, description: la koloro de la ĉielo, la libro de mia patro. The test is one question: is the first word measuring the second? If yes, da. If it is merely relating to it, de.

po, and the argument about it

Po marks a rate: so much each.

Mi donis al la infanoj po tri libroj. - I gave the children three books each.

Po is a preposition, and Esperanto prepositions are followed by the nominative unless -n is doing its motion job. So po tri libroj, without the -n. You will nonetheless meet po tri librojn in perfectly respectable writing, because the phrase feels like the object of the verb and usage has never entirely settled. I would write it without. It is a small argument, and the sentence is clear either way.

Keep po and -op- apart while they are new: po du is two each, duope is two at a time.

What to take away

• Nine roots plus dek, cent, mil, and that is the whole vocabulary.
• Multiply joins up (dudek), add stays apart (dek du).
• Cardinals never take -j or -n.
• -a ordinal, -on- fraction, -obl- multiple, -op- collective.
• Da after a quantity word, nothing after a bare numeral, de for everything else.

An afternoon on this and numbers stop being vocabulary and start being arithmetic you can spell.