Examples:
Mi estas malsata = Mi malsatas
Tio estus bona = Tio bonus
Are there rules about when this is not allowed? Or can any adjective be turned into a verb at any time?
Esperanto Language Stack Exchange is a question and answer site for teachers and students of the Esperanto language. It only takes a minute to sign up.
Sign up to join this communityOther than in cases where the verb form has a different meaning, like the case of "morta" mentioned by Clayton; basically if the adjective is considered the basic form of the word, you can use the root as a verb meaning "to be X". But there are some stylistic considerations to keep in mind, which influence whether the verb form sounds natural or not. Primarily, the purpose of a verb is to express an action or state of being. So, adjectival verbs are most commonly used for transient states or conditions, and not as commonly for inherent attributes or characteristics. For example, "mi malsatas"; I am currently hungry, but hungriness is not an inherent characteristic of me. "La cxielo bluas"; the sky is blue, as opposed to being black, or grey, or pink and orange at the edges fading to a nondescript greyish at the top... But it would be unusual to say "la monto grandas", because big-ness is an inherent characteristic of mountains; it's not that the mountain is in a state of being big now, as opposed to all those times that it's not big. That being said, sentences like "la monto grandas" or "li pli altas ol mi" are not incorrect, only stylistically unusual, and you will see such uses, especially in poetry where there are rhyme and meter constraints, or one finds that the verb form just feels more poetic.
Note also, that using "estas X" does not imply that something is an inherent characteristic, it is perfectly normal to say, for example, "mi estas malsata".
I hope this is clear, the basic summary is that there isn't a hard-and-fast rule, but verb forms of adjective roots are in general used more often for temporary states or conditions than for permanent characteristics.
In order to understand how a word can shift in meaning when it is changed into another word class, you need to understand that Esperanto word roots can be grouped into three categories: - Adjectival word roots that express a property and whose base form is an adjective, e.g. "bon/", "grand/" and "sat/", whose base forms are "bona", "granda" and "sata". - Verbal word roots that express an action, event or state, and whose base form is a verb, e.g. "bat/", "fal/" and "sid/", whose base forms are "bati", "fali" and "sidi" - Nominal word roots, whose base forms are nouns, e.g. "tabl/", "ide/" and "nombr/", whose base forms are "tablo", "ideo" and "nombro".
You can always add a verb ending to an adjectival word root X in order to get a verb "X-i" that means something very close (or identical) to "esti X-a". But there are also adjectives that are not formed from adjectival roots, but are derived from verbal or nominal roots by making them into adjectives. In that case the meaning of the "X-i" will not necessarily be related to the meaning of "X-a" in this way.
For example, "inform/" is a verbal root, so its abase form is "informi" ("to inform"). The adjective "informa" means "informative", but you cannot derive back "informi" with the meaning "to be informative" from it, as "informi" already means "to inform".
For an example with a nominal root, take "trajn/", whose base form is "trajno" ("train"). One can derive the verb "trajni" ("to travel by train") from it. Furthermore, you can derive the adjective "trajna" ("by train or related to trains") from it. For example, you can say "Nia vojaĝo estis parte trajna kaj parte busa" ("Our journy was partially by train and partially by bus"). But you shouldn't say "Nia vojaĝo parte trainis", as "trajni" already means "to travel by train", and it isn't logical to say that the journey travelled by train.
As far as I know, the only time when one shouldn't is if there is already a verb where it should be. For instance, "morta" means "dead," but "morti" means "to die." In general, it appears as though adjectival verbs primarily relate to becoming the state of the verb, as opposed to neutrally being in that state.
I'm not sure whether one can do this with participle adjectives (-anta, -inta, -onta, -ata, -ita, and -ota) and would greatly appreciate if someone else knew whether this is applicable.
Just to go back to an earlier comment (an what appears to be an old thread), la monto grandas would not be common to use, since there is no change of state, the mountains are big, and remain big. If they grow big, as they indeed would over a long time, you would probably say grandiĝas.
I was thinking, in terms of poetry, however, that the difference might be thus:
La monto estas granda - "the mountain is big"
La monto grandas - "the mountain looms" (ie, its experienced bigness seems to become more prominent. Not an objective description, but a subjective one, one of perception, subtly conveying a similar meaning, perhaps, to something like La monto ŝajnas al mi, ke ĝi grandiĝus.)
I've not been learning Esperanto long, but that's the kind of feeling I have of the nuance in difference between an adjective and a verb derived from one.