Learn Hardcore Finnish: Opettaja selitti romaanin juonen lyhyesti. - The teacher explained the plot of the novel briefly.

Why is there no word for “the” in “Opettaja selitti romaanin juonen lyhyesti”? How do I know if it means “a teacher” or “the teacher”?

Finnish has no articles (a, an, the) at all. The noun opettaja just means “teacher” in a neutral way.

Whether you translate it as “a teacher” or “the teacher” depends entirely on context:

In a typical classroom story, you’d naturally translate: “The teacher explained the plot of the novel briefly.”
In a more general statement, it could be: “A teacher explained the plot of the novel briefly.”

Finnish relies on context, word order, and sometimes pronouns or modifiers to show whether something is specific or not, but it never uses an article word like English does.

What exactly is selitti? Which verb is it from, and what tense/person is it?

Selitti is the past tense of the verb selittää = “to explain”.

Infinitive (dictionary form): selittää – to explain
Stem: selittä-
Past tense ending: -i
3rd person singular ending: (no extra ending in past)

So:

hän selitti = he/she explained
opettaja selitti = the teacher explained

You form it by taking the stem selittä- and adding -i: > selittää → selitti

What case is romaanin, and why does it end in -n?

Romaanin is the genitive singular of romaani (a novel).

romaani = novel (nominative)
romaanin = of the novel (genitive)

Here it works like “the novel’s plot”:

romaanin juoni = the novel’s plot / the plot of the novel

So romaanin is marking a possessive/”belonging to” relationship: the plot belonging to the novel.

Why do both romaanin and juonen end in -n? Are they in the same case?

They both look like genitive, but they play slightly different roles:

romaanin is genitive and acts as an attribute:
romaanin juoni = the novel’s plot
juonen is the direct object of selitti.
For full nouns in the singular, the “total object” form often looks identical to the genitive. So grammars may call it genitive object or accusative with genitive form.

Functionally, you can think:

romaanin – whose plot? → the novel’s (plot)
juonen – what did the teacher explain? → the plot

So both end with -n, but:

one shows relationship/possession (romaanin),
the other marks the complete object of the verb (juonen).

Why is it juonen and not juoni or juonta?

The noun juoni (“plot”) has these important forms:

juoni – nominative (subject form)
- Juoni oli monimutkainen. – The plot was complicated.
juonen – genitive / total object
- Opettaja selitti juonen. – The teacher explained the (whole) plot.
juonta – partitive object
- Opettaja selitti juonta. – The teacher was (kind of) explaining the plot / explained part of the plot.

In your sentence:

Opettaja selitti romaanin juonen lyhyesti.

the idea is that the teacher explained the entire plot in a short form → a completed, whole object, so juonen (total object) is used, not juonta.

Using juoni (nominative) here would simply be wrong grammar as an object.

Can the word order change? For example, is “Opettaja selitti lyhyesti romaanin juonen” also correct?

Yes, Finnish word order is quite flexible, and both are correct:

Opettaja selitti romaanin juonen lyhyesti.
Opettaja selitti lyhyesti romaanin juonen.

The basic meaning is the same. Word order mainly affects emphasis:

Putting lyhyesti at the end is very neutral:
focus is slightly on what was explained (the plot), and how is added at the end.
Putting lyhyesti earlier can highlight the manner more:
The teacher explained, and did so briefly, the plot of the novel.

You can even front the object for emphasis:

Romaanin juonen opettaja selitti lyhyesti.
→ Emphasis on “the plot of the novel” (perhaps in contrast to something else that wasn’t explained).

What does lyhyesti literally mean, and how is it formed?

Lyhyesti means “briefly / in short”.

It is formed from the adjective lyhyt = short:

Take the adjective stem: lyhyt → lyhye-
Add -sti, which typically forms adverbs from adjectives.
lyhye- + -sti → lyhyesti

Parallel examples:

nopea (fast) → nopeasti (quickly)
selvä (clear) → selvästi (clearly)
pitkä (long) → pitkästi (long-windedly / at length, in some contexts)

So lyhyt (short) → lyhyesti (in a short way, briefly).

Could I say “Opettaja antoi lyhyen selityksen romaanin juonesta” instead? What’s the difference?

Yes, that sentence is also correct, but the structure changes:

Opettaja selitti romaanin juonen lyhyesti.
→ The teacher briefly explained the plot of the novel.
(verb selitti
- object romaanin juonen
  - adverb lyhyesti)
Opettaja antoi lyhyen selityksen romaanin juonesta.
→ The teacher gave a short explanation of the plot of the novel.
(verb antoi “gave” + noun phrase lyhyen selityksen “a short explanation” + romaanin juonesta “about/from the plot of the novel”)

Notes:

lyhyen selityksen – adjective + noun, both in genitive/accusative (a single “short explanation” as object)
romaanin juonesta – elative case (-sta/-stä), literally “from/out of the novel’s plot”, idiomatically “about the novel’s plot”.

The first sentence is more direct and verb-based; the second is more nominal and a bit more formal in style.

Can I leave out romaanin and just say “Opettaja selitti juonen lyhyesti”?

Yes, that is grammatical and natural if the context already makes clear which plot you’re talking about.

Opettaja selitti juonen lyhyesti.
→ The teacher briefly explained the plot. (of whatever story/novel is understood from context)

If you need to introduce that it’s the plot of a novel specifically (and not, say, a film or a short story), then you keep romaanin:

Opettaja selitti romaanin juonen lyhyesti.

So: you can omit romaanin when it’s obvious, but then you also lose that specific information.

Does lyhyesti sound neutral, or does it suggest the explanation was too short or lacking detail?

Lyhyesti by itself is neutral. It just says that the explanation was brief/concise, without judging whether that was good or bad.

The evaluation comes from context or extra words:

vain lyhyesti – only briefly (may suggest “not enough”)
hyvin lyhyesti – very briefly (could be positive or negative)
lyhyesti ja selkeästi – briefly and clearly (clearly positive)

So in your sentence, lyhyesti is simply descriptive: the teacher gave a short summary.

Is romaani only “novel”, or can it also mean any book?

Romaani specifically means a novel, i.e., a long fictional prose work.

romaani – novel
kirja – book (any kind of book: textbook, novel, manual, etc.)

So:

romaanin juoni = the plot of the novel
kirjan juoni would sound odd unless the “book” is clearly a story book / novel (people usually still say romaani for a novel).

If you just mean a book in general, use kirja; if you specifically mean a novel as a literary genre, use romaani.