Editing Esperanto grammar (section)

==Numbers==

===Numerals===
The [[Cardinal number|cardinal]] [[Numeral (linguistics)|numerals]] are:

:''nul'' (zero)
:''unu'' (one)
:''du'' (two)
:''tri'' (three)
:''kvar'' (four)
:''kvin'' (five)
:''ses'' (six)
:''sep'' (seven)
:''ok'' (eight)
:''naŭ'' (nine)
:''dek'' (ten)
:''cent'' (hundred)
:''mil'' (thousand)

Grammatically, these are numerals, not nouns, and as such do not take the accusative case suffix ''-n''. However, ''unu'' (and only ''unu'') is sometimes used adjectivally or demonstratively, meaning "a certain", and in such cases it may take the plural affix ''-j,'' just as the demonstrative pronoun ''tiu'' does:
:''unu'''j''' homo'''j''''' "certain people";
:''ili kuris unu'''j''' post la aliaj'' "they ran some after others".
In such use ''unu'' is irregular in that it only rarely takes the accusative/prepositional case affix ''-n'' in the singular, but regularly does so in the plural:
:''ia'''n''' unu ideo'''n''''' "some particular idea",
but
:''unuj objektoj venis en unu'''jn''' mano'''jn''', aliaj en aliajn manojn'' "some objects came into certain hands, others into other hands".
Additionally, when counting off, the final ''u'' of ''unu'' may be dropped, as if it were a part-of-speech suffix:
:''Un'! Du! Tri! Kvar!''

===Higher numbers===
At numbers beyond the thousands, the international roots ''miliono'' (million) and ''miliardo'' (milliard) are used. Beyond this there are two systems: A ''[[Long and short scales|billion]]'' in most English-speaking countries is different from a ''billion'' in most other countries (10<sup>9</sup> ''vs.'' 10<sup>12</sup> respectively; that is, a thousand million ''vs.'' a million million). The international root ''biliono'' is likewise ambiguous in Esperanto, and is deprecated for this reason. An unambiguous system based on adding the Esperanto suffix ''-iliono'' to numerals is generally used instead, sometimes supplemented by a second suffix ''-iliardo:''<ref>"[https://reta-vortaro.de/revo/art/bilion.html biliono]" at Reta Vortaro</ref>

:10<sup>6</sup>: ''miliono''
:10<sup>9</sup>: ''miliardo'' (or ''mil milionoj'')
:10<sup>12</sup>: ''duiliono''
:10<sup>15</sup>: ''duiliardo'' (or ''mil duilionoj'')
:10<sup>18</sup>: ''triiliono''
:10<sup>21</sup>: ''triiliardo'' (or ''mil triilionoj'')
:''... etc.''

Note that these forms are grammatically nouns, not numerals, and therefore cannot modify a noun directly: ''mil homojn'' (a thousand people [accusative]) but ''milionon da homoj'' (a million people [accusative]).

===Compound numerals and derivatives===
Tens and hundreds are pronounced and written together with their multipliers as one word, while all other parts of a number are pronounced and written separately (''dudek'' 20, ''dek du'' 12, ''dudek du'' 22, ''dek du mil'' 12,000).<ref>[https://bertilow.com/pmeg/gramatiko/nombroj/vortetoj/formoj.html ''Plena Manlibro de Esperanta Gramatiko'']</ref> Ordinals are formed with the adjectival suffix ''-a,'' quantities with the nominal suffix ''-o,'' multiples with ''-obl-,'' fractions with ''‑on‑'', collectives with ''‑op‑'', and repetitions with the root ''‑foj‑''.

:''sescent sepdek kvin'' (675)
:''tria'' (third [as in ''first, second, third''])
:''trie'' (thirdly)
:''dudeko'' (a score [20])
:''duobla'' (double)
:''kvarono'' (one fourth, a quarter)
:''duope'' (by twos)
:''dufoje'' (twice)

The particle ''po'' is used to mark distributive numbers, that is, the idea of distributing a certain number of items to each member of a group:
:''mi donis al ili po tri pomojn'' or ''pomojn mi donis al ili po tri'' (I gave [to] them three apples each).

Note that particle ''po'' forms a phrase with the numeral ''tri'' and is not a preposition for the noun phrase ''tri pomojn,'' so it does not prevent a grammatical object from taking the accusative case.