Page "Esperanto grammar" Paragraph 36

Each root word has an inherent part of speech: nominal, adjectival, verbal, or adverbial.

These must be memorized explicitly and affect the use of the part-of-speech suffixes.

With an adjectival or verbal root, the nominal suffix-o indicates an abstraction: parolo ( an act of speech, one's word ) from the verbal root paroli ( to speak ); belo ( beauty ) from the adjectival root bela ( beautiful ); whereas with a noun, the nominal suffix simply indicates the noun.

Nominal or verbal roots may likewise be modified with the adjectival suffix-a: reĝa ( royal ), from the nominal root reĝo ( a king ); parola ( spoken ).

The various verbal endings mean to be when added to an adjectival root: beli ( to be beautiful ); and with a nominal root they mean to act as the noun, to use the noun, etc., depending on the semantics of the root: reĝi ( to reign ).

There are relatively few adverbial roots, so most words ending in-e are derived: bele ( beautifully ).

Often with a nominal or verbal root, the English equivalent is a prepositional phrase: parole ( by speech, orally ); vide ( by sight, visually ); reĝe ( like a king, royally ).