Valency categories are a feature of classical European grammar so basic they're often taken for granted; they regulate the number of noun phrases that can be associated as arguments with a given verb (or other wordclass, but never mind that for now).
- One argument: It¹ exists
- Two arguments: I¹ seek the Holy Grail²
- Three arguments: Sam¹ lent me² this hat³
Excluding commands with omitted subjects (“stop!”), zero‐argument verbs don't occur in English; Esperanto behaves like a Slavic language by expressing “(it)'s raining” as pluvas.
Compared to the European standard model, English has somewhat relaxed valency rules, allowing many verbs to occur with any number of arguments (“give”: “please give generously; I gave earlier; cows give milk; she gave me this”). Grammar books warn that no such “illogical” behaviour is tolerated from Esperanto verbs – an intransitive‐to‐transitive valency change may be obvious from the accompanying noun cases, but it must also be signalled with the suffix ‑ig = “cause, render”, like this:
- boli = “to bubble, to boil (intransitive)” → boligi = “to cause to bubble, to boil (transitive)” – Esperantists are always full of disdain for the ambiguity of English words like boil;
- manĝi = “to eat” → manĝigi, which can mean “to cause to eat, to serve food to” or “to cause to be eaten, to serve as food” – you'd think it would be worth avoiding mix‐ups here, but dictionaries assure me it can mean either…
- naski = “to give birth to” (the transitive verb indicating what a mother does to a baby) → naskigi = “to beget” (what the father did nine months earlier). Shouldn't it mean either “cause to give birth” or “cause to be born” (either way, a job for a qualified obstetrician)?
What was that about logic?
Meanwhile, there's the case where a single entity occupies both subject and object slots – reflexives, which you'd think “logically” might get some similar valency‐modifying suffix. Instead they're handled as normal transitives with a special pronoun: ili vidis sin = “they saw themselves”. The rules for reflexives are just a direct copy of the continental‐European grammatical standard, including random details like the way reciprocals (such as “they saw one another”) can work either as reflexives (ili vidis sin reciproke) or non‐reflexive constructions (ili vidis unu la alian). Otherwise the use of si is mandatory any time you refer back reflexively to a third‐person subject with a pronoun, even if it's the kind of possessive pronoun that's disguised as an adjective: ili vidis siajn = “they saw their own ones” (only within the same clause, though; “they said they were their own ones” uses iliaj). However, there's one detail of reflexive pronoun usage that Zamenhof's source languages disagree on: can it be used in the first and second person? The Slavic languages say yes, but for once Esperanto doesn't follow their lead, so it's vi vidis vin = (literally) “you saw you”. The explanation is that this rule was introduced not by Zamenhof but by early Esperantists from Germany and France.
The subtleties of valency categories wouldn't matter so much if they weren't critical to passivisation, which converts any two‐argument verb to a special one‐argument form. Converting an active sentence like mi legis la libron = “I read the book” involves four steps, in English or Esperanto:
- Simple tenses become compounds: legis → estas leginta
- Active participles become passive: leginta → legita
- The subject is demoted to a “by phrase”: mi → de mi
- The object is promoted in its place: libron → libro
So “the book was read by me” = la libro estas legita de mi.
One extra possibility that English allows to mislead anglophone Esperantists is the promotion of indirect objects (“I was lent this hat by Sam”). It seems reasonable that Esperanto doesn't permit anything quite like that… but Esperanto passives also have a stranger limitation. La libro estas legita de mi is also what you get if you go through the passivisation process starting from mi estas leginta la libron = “I have read the book”. So does that passive construction mean “was read” or “has been read”, and whichever it is, why is there no clear way of saying the other one?
It's not even as if Esperanto really needs all these complex passivisation rules. The point of passives is to give centre stage to the “Patient” of a situation rather than the “Agent”, and most modern European languages provide easier ways of doing that. Esperanto should never have needed the construction at all when it (at least potentially) has options like:
- Topicalising reshuffles: la libron mi legis
- Special vague pronouns: oni/iu(j) legis la libron
- Unspecific subjects: homo(j)/ulo(j) legis la libron
- Zero subjects: — legis la libron
One alternative to passive constructions that gets into Esperanto from various European languages is a convoluted use of ‑iĝ, the intransitive converse of ‑ig, in a “mediopassive” sense. La libro iĝis ruĝa = “the book became red”; la libro ruĝiĝis = “the book reddened”; and by analogy, la libro legiĝis = “the book got read”. Just as with ‑ig the logic of this is then stretched to breaking point by verbs like sciiĝi, a tonguetwister that ought to mean “to get known, spread (as news)”, but is instead used as “to become aware”. Zamenhof even used it with an object as an approximate synonym of “to learn”.