Official Esperanto: Fundamento, official roots, dictionaries

Esperanto has three levels of authority. The Fundamento de Esperanto of 1905 is fundamental: it binds every speaker and cannot be changed. The roots added since 1909 by ten Oficialaj Aldonoj (Official Additions, 1OA–10OA) and three single decisions are official, which means a strong recommendation. Everything else is ordinary usage: words made by regular word building, newer loanwords, and the big dictionaries PIV and ReVo, which are respected but not official.

The body that keeps the official list is the Academy of Esperanto. The sections below show what each level contains, how to check a word, and which unofficial words are safe.

#The layers of Esperanto at a glance

The Academy counts "elements": roots, affixes, small words and endings. Counts for the Additions are the Academy's; totals are our own sums.

#Timeline of official Esperanto

The early years are told in the history of Esperanto.

#What is fundamental in Esperanto?

Fundamental means "found in the Fundamento de Esperanto". The Academy defines a Fundamental element as any element in the book's dictionary, exercises, grammar or foreword. It counts 2,768 of them. The grammar part holds the 16 rules, and much of the book comes from the Unua Libro. You can read the whole book, unchanged, in our Fundamento de Esperanto section.

On 9 August 1905 the Declaration of Boulogne made the Fundamento the only basis binding on all Esperantists for all time. Nobody may change it: the text says neniu havas la rajton fari ŝanĝon – "nobody has the right to make a change". Zamenhof himself had no special power. His other opinions and works are private and bind no one.

The Declaration still leaves room for growth. Any idea that the Fundamento cannot express conveniently, each speaker may express in the way he finds most correct, as in every other language. It only recommends imitating Zamenhof's style, for the sake of unity.

The old translations in the book contain mistakes, and they stay in the text. The Language Committee prepared corrections in 1906–1913 and published them in 1922–1923; the Academy's dictionary uses them.

#What does official mean in Esperanto?

An official element is one that the Academy, or the Language Committee before it, decided to add to the Universala Vortaro. Formally the root joins the dictionary that belongs to the Fundamento, but it does not become Fundamental. The Academy's text on the 9th Addition says that only elements of the original, untouchable Fundamento are Fundamental, and that official status in practice has the character of a strong recommendation.

The Academy says it can neither compel nor wants to compel language use. Article 22 of its statute allows decisions that are only recommendations or discouragements. Official definitions also cover only the core meanings: many words have further unofficial senses.

#Official roots by layer

The Fundamento supplies more elements (2,768) than the ten Additions together (2,602). The first Addition is the largest, and the fifth added only eight.

The Academy's own table stops at 2007 with 4,953 official elements (2,768 Fundamental and 2,185 official). Adding the 420 roots of 2023 gives about 5,373. These are a small part of the vocabulary; the rest is normal Esperanto built by the rules in word building.

#Official dictionaries – and the ones that are not

Strictly, the official dictionary is the Universala Vortaro of the Fundamento together with the Official Additions. The Academy merges them in the online Akademia Vortaro. No full-size dictionary of Esperanto is official.

PIV was compiled under Gaston Waringhien and has 16,780 headwords in the 2002 and 2005 editions. Vikipedio calls it a quasi-standard reference work, and many of its 59 first collaborators were Academy members, yet it is SAT's publication, not the Academy's. Its online version lets you filter entries as Fundamental, official or unofficial, so PIV treats officiality as a label on words, not as a property of the book. For a comparison of tools, see the best Esperanto dictionaries.

#Unofficial roots: normal, new or best avoided

An unofficial root is not an error. Grammarian Bertilo Wennergren writes in PMEG that new ordinary roots enter the language easily, because no special rules apply to them. New affixes are different: they rarely become established, and those that collide with existing words are highly avoidable.

Normal words that are not on the list. We checked these on 8 October 2026.

Words that became official late. The 9th Addition added komput- ("to compute"), aspirin-, avokad-, bit- and pic- to the list only in March 2007, and the 8th added sandviĉ- in 1974. Until then these roots were unofficial.

Forms best avoided. The clearest warning concerns a reform, not a root: building a new correlative series on ali-. PMEG calls it an "evitenda reformo" (reform to avoid), and ReVo calls these forms unofficial and avoidable. They would also change the meaning of the ordinary alie.

The rule of thumb: a new ordinary root is fine if it is clear and others use it. A new affix, or a new pattern in the grammar, needs a strong reason.

#How to check a word

1. Fundamento. If the word, rule or affix is in the Fundamento, the matter is settled.
2. Akademia Vortaro. Search for the bare root, not the whole word: komput for komputilo. The result shows F (Fundamental), 1OA–10OA, a single-decision year, or a BRO group. If the bare root is not found, it is not on the official list.
3. PMEG. The Plena Manlibro de Esperanta Gramatiko explains grammar and word building. It is a respected reference, not an official one.
4. ReVo and PIV. They show how a word is used. ReVo notes neologisms and marks official roots.
5. Build it. If no dictionary has the word, make it from official roots by regular rules, and prefer clear, short forms.

#How our dictionary shows it

On entry pages of our dictionary, a badge near the word shows its officiality, taken from ReVo's marks. Words on the list show "Official word (Fundamento)" (hundo) or "Official word (9. Oficiala Aldono)" (komputilo). Words derived from an official root show "Official root komput- (9. Oficiala Aldono, 2007)" (komputado). Each badge links to the list of its layer.

The list of all official roots by layer is at esperantopedia.org/dictionary/oficialaj-radikoj/. It counts one root per entry marked as official in ReVo, while the Academy counts elements: roots, affixes, small words and endings. That is why our list has 5,328 instead of about 5,373.

#Common questions

#Who decides what is correct Esperanto?

The Fundamento is the only binding authority, and the Academy interprets it and recommends usage. Beyond that, correctness comes from clear use by competent speakers, with references such as PMEG.

#Is PIV the official Esperanto dictionary?

No. SAT publishes PIV, not the Academy, and official status belongs only to elements that the Academy or the Language Committee added to the Universala Vortaro. Many speakers treat PIV as the standard reference, and its online version can filter words as Fundamental, official or unofficial. The official list is the Akademia Vortaro.

#Is a word wrong if it is not official?

No. The official list is a core, not the whole language. Words like dosiero and plaĝo are normal, and the Declaration of Boulogne lets every speaker express new ideas in the way he finds most correct.

#How many official roots does Esperanto have?

The Academy counts 4,953 official elements up to 2007: 2,768 Fundamental and 2,185 official. The 420 roots of 2023 bring the total to about 5,373. Our list, based on ReVo, counts roots rather than elements and has 5,328.

#Can the Fundamento be changed?

No. The Declaration of Boulogne put it beyond change in 1905. The Academy can add roots through Official Additions, but it cannot alter the Fundamento. Even known translation errors stay in the text and are corrected in separate documents.

#What is the BRO?

The Baza Radikaro Oficiala ranks 2,461 elements in nine frequency groups. The Academy published it in 1968–1974, together with the 8OA. It adds no new words, and the Academy calls it a help, not a law. For modern counts see the 100 most common words.

#Sources

• Akademio de Esperanto – Akademia Vortaro (search)
• Akademio de Esperanto – Akademia Vortaro: Klarigoj
• Akademio de Esperanto – Statuto
• Akademio de Esperanto – Fundamento
• Akademio de Esperanto – Naŭa Oficiala Aldono (2007)
• Akademio de Esperanto – Deka Oficiala Aldono (2023)
• Akademio de Esperanto – Baza Radikaro Oficiala (Aktoj II, 1968–1974)
• Vikipedio – Oficialaj aldonoj
• Vikipedio – Baza Radikaro Oficiala
• Wikipedia – Declaration of Boulogne
• David K. Jordan – The Boulogne Declaration (Esperanto text with English translation)
• Wikipedia – Fundamento de Esperanto
• Vikipedio – Plena Ilustrita Vortaro
• Wikipedia – Plena Ilustrita Vortaro de Esperanto
• PIV 2020 at vortaro.net (officiality filter; entries checked 8 October 2026)
• ReVo – Statistiko
• ReVo – article ali (note under alie)
• ReVo – article blog
• Wikipedia – Reta Vortaro
• PMEG – Ĉu ALI-vortoj povas esti tabelvortoj?
• PMEG – Neoficialaj afiksoj