Learn Hardcore Finnish: Selitän ystävälle lyhyesti, millainen juoni kirjassa on. - I briefly explain to my friend what kind of plot the book has.

movement onto / to something: pöydälle = onto the table
and very often for the indirect object, the person you say/give/explain something to:
Selitän ystävälle asian. = I explain the matter to a friend.
Annoin kirjan ystävälle. = I gave the book to a friend.

So in this sentence, ystävälle marks the person to whom you are explaining something.

Could I say ystävälleni for “to my friend”? How is that different from ystävälle?

Yes:

ystävälle = to a friend / to the friend (no possession expressed)
ystävälleni = to my friend

Ystävälleni is built like this:

ystävä (friend)
- -lle (allative: to) → ystävälle
- -ni (possessive suffix: my) → ystävälleni

So:

Selitän ystävälle lyhyesti… = I briefly explain (it) to a friend / to the friend.
Selitän ystävälleni lyhyesti… = I briefly explain (it) to my friend.

You can also say minun ystävälleni (literally “to my friend”) for extra clarity or emphasis, but ystävälleni alone is completely natural.

What person and tense is selitän, and can it also mean “I will explain”?

Selitän is:

verb: selittää = to explain
person/number: 1st person singular (“I”)
tense: present indicative

So selitän = I explain.

In Finnish, the present tense often covers near future as well, just like in English:

Huomenna selitän ystävälle, millainen juoni kirjassa on.
= Tomorrow I (will) explain to my friend what the plot of the book is like.

If you really want to emphasize the future, you can use something like:

Aion selittää… = I am going to explain…

Where is the direct object of selitän in this sentence?

The “object” of selitän here is not a single word, but the whole clause:

millainen juoni kirjassa on
what the plot in the book is like

So structurally:

Selitän
- (ystävälle) = to a friend
- (lyhyesti) = briefly
- millainen juoni kirjassa on = what the plot in the book is like (content clause)

In Finnish grammar this is called an object-like content clause or an indirect question (epäsuora kysymyslause). It fills the same role as a direct object would:

Selitän asian. = I explain the matter.
Selitän, millainen juoni kirjassa on. = I explain what the plot in the book is like.

You don’t need an extra pronoun like sen (it) here. The clause itself is enough.

How is lyhyesti formed, and why not lyhyt or lyhytsti?

Lyhyesti is the adverb “briefly”, formed from the adjective lyhyt (“short”).

Pattern: adjective + -sti → adverb

nopea → nopeasti = quick → quickly
selvä → selvästi = clear → clearly
lyhyt → lyhyesti = short → briefly

With lyhyt, the stem changes a bit:

adjective stem: lyhye- (seen in forms like lyhyeen)
- -sti → lyhyesti

So:

lyhyt = short (adjective)
lyhyesti = briefly, in a short way (adverb)

Lyhytsti doesn’t exist, and using just lyhyt would be wrong here, because Finnish, like English, uses an adverb form with verbs:

Selitän lyhyesti. = I explain briefly.
(not I explain short.)

Where can lyhyesti go in the sentence? Is the current word order fixed?

The given word order is very natural:

Selitän ystävälle lyhyesti, millainen juoni kirjassa on.

But Finnish word order is fairly flexible, and lyhyesti can move a bit. Some common possibilities:

Original (very natural):
- Selitän ystävälle lyhyesti, millainen juoni kirjassa on.
Adverb earlier (still natural):
- Selitän lyhyesti ystävälle, millainen juoni kirjassa on.
  This slightly foregrounds the brevity of the explanation.
At the end (marked / more stylistic):
- Selitän ystävälle, millainen juoni kirjassa on, lyhyesti.
  Understandable, but sounds more like a rhetorical or written style, with a pause:
  “I explain to my friend what the plot in the book is like — briefly.”

For everyday neutral style, options 1 and 2 are best. The meaning doesn’t change much; it’s mostly about emphasis and rhythm.

What exactly does millainen mean here, and how is it different from mikä?

Millainen is an interrogative / relative pronoun meaning “what kind of, what sort of, what … like”.

In this sentence:

millainen juoni = what kind of plot / what the plot is like

So:

Selitän …, millainen juoni kirjassa on.
I explain … what kind of plot the book has / what the plot is like.

Difference from mikä:

mikä = what / which (thing), often identifying something
millainen = what kind of, describing the quality or type

Compare:

Mikä kirja tämä on? = What book is this? (which one)
Millainen kirja tämä on? = What kind of book is this? (funny, boring, long…)

Using mikä here would sound wrong or at least unnatural, because we’re not asking which plot, but what the plot is like.

Note: you may also see minkälainen; it’s essentially a variant of millainen.

Why is there a comma before millainen?

In standard written Finnish, you normally put a comma before a subordinate clause, including indirect questions introduced by words like mitä, kuka, millainen etc.

So you write:

Selitän ystävälle lyhyesti, millainen juoni kirjassa on.

This comma separates:

main clause: Selitän ystävälle lyhyesti
subordinate clause: millainen juoni kirjassa on

English would often omit this comma:

I’ll briefly explain to my friend what the plot of the book is like.

But Finnish typically keeps it. In informal writing you sometimes see the comma dropped, but the recommended standard form has the comma.

Why is the verb on at the end of millainen juoni kirjassa on? Could it come earlier?

In indirect questions like this, a common and very natural pattern is:

question word – subject – other elements – verb

So here:

millainen (question word)
juoni (subject)
kirjassa (locative phrase “in the book”)
on (verb “is”)

→ millainen juoni kirjassa on

You can change the order a bit:

millainen juoni on kirjassa – grammatical, but less common and with a slightly different emphasis
millainen kirjan juoni on – also grammatical; here you use kirjan juoni (“the book’s plot”) as a unit

However, millainen juoni kirjassa on is the most neutral and idiomatic for “what the plot in the book is like.” Keeping on at the end of such subordinate clauses is very typical Finnish word order.

Why is it kirjassa (“in the book”) and not kirjan juoni (“the book’s plot”)?

Both are possible, but they frame the idea slightly differently:

kirjassa = in the book (inessive case, -ssa)
- juoni kirjassa = a / the plot in the book
- millainen juoni kirjassa on ≈ what kind of plot there is in the book
kirjan juoni = the book’s plot (genitive + noun)
- kirjan juoni = the plot of the book
- millainen kirjan juoni on ≈ what the book’s plot is like

In practice, the meaning is almost the same here. The choice is more about perspective:

kirjassa emphasises something located in the book (“there is a plot in the book, and what is it like?”).
kirjan juoni emphasises a property of the book (“the plot of the book, what is it like?”).

You could perfectly well say:

Selitän ystävälle lyhyesti, millainen kirjan juoni on.

and it would be natural Finnish.

Can I add että before millainen, like Selitän ystävälle lyhyesti, että millainen juoni kirjassa on?

No, that’s not correct in standard Finnish.

You have two different ways to introduce content clauses:

että-clause (a “that”-clause, statement-like):
- Selitän, että juoni kirjassa on monimutkainen.
  = I explain that the plot in the book is complicated.
interrogative word (indirect question):
- Selitän, millainen juoni kirjassa on.
  = I explain what the plot in the book is like.

You don’t combine että with millainen / mitä / kuka in this way. So:

✅ Selitän, millainen juoni kirjassa on.
✅ Selitän, että juoni kirjassa on tällainen.
❌ Selitän, että millainen juoni kirjassa on.

Why is nothing in the partitive case here? I often see partitive used with verbs.

There’s no partitive here because the roles in the sentence simply don’t call for it:

Selitän – verb, present
ystävälle – allative (indirect object: to whom)
lyhyesti – adverb
millainen juoni kirjassa on – content clause (what is being explained)
- inside it:
  - juoni – subject (nominative)
  - kirjassa – inessive (location: in the book)
  - on – verb

Key points:

The verb selittää takes either a noun phrase object (Selitän asian.) or a clause (Selitän, millainen juoni kirjassa on.).
In this sentence we have the clause, so there is no noun object that could even be in the partitive.
The noun juoni is a subject of on, not an object, so it appears in the nominative, not in the partitive.

So while Finnish does use the partitive very often, this particular sentence doesn’t have a context where the partitive would be needed.