Learn Hardcore Finnish: Illalla istun sohvalle ja luen kirjaa lattialampun vieressä olevan sohvapöydän ääressä. - In the evening I sit on the sofa and read a book at the coffee table next to the floor lamp.

Besides the basic meaning “on / at something” (e.g. pöydällä = on the table), the adessive is very commonly used with times of day to mean “at that time”:

aamulla – in the morning
päivällä – in the daytime
illalla – in the evening
yöllä – at night

So Illalla means “in the evening / at night” in a general sense (“this evening / in the evenings”), and the -lla here is a normal way to express “at that time of day” in Finnish.

Why is there no minä in the sentence? How do we know it means “I”?

Finnish is a pro‑drop language: the personal pronoun is often left out because the verb ending already shows the person.

istun = I sit / I am sitting
luen = I read / I am reading

The -n ending marks first person singular, so adding minä would be optional:

Illalla *minä istun sohvalle ja luen kirjaa…*

That version is also correct, but it has more emphasis on minä (“I, as opposed to someone else, sit on the sofa…”). The neutral, most natural version usually just omits the pronoun.

Why is it istun sohvalle and not istun sohvalla?

Finnish uses different cases to show movement to a place versus being at a place:

sohvalle – illative (-lle), “onto the sofa”, movement to the sofa
sohvalla – adessive (-lla), “on the sofa”, being on the sofa

So:

istun sohvalle = I sit down onto the sofa (the act of going to sit there)
istun sohvalla = I sit / I am sitting on the sofa (describing the state/location)

Your sentence describes the action of going to sit down, so sohvalle is used.
If you just wanted to state where you are when reading, you could also say:

Illalla *istun sohvalla ja luen kirjaa…* – “In the evening I sit on the sofa and read a book.”

Why is it luen kirjaa (partitive) and not luen kirjan?

Kirjaa is the partitive singular of kirja (“book”). With many verbs, the choice between partitive and total object (e.g. kirjan, accusative/genitive) expresses whether the action is seen as ongoing / incomplete / unbounded or complete / whole.

luen kirjaa
– “I am reading a book / I read (some) book.”
– The action is ongoing, not presented as finished.
– Often also feels more indefinite: some book, not a specific whole one from cover to cover.
luen kirjan
– “I (will) read the book (completely).”
– Implies reading the whole book, with a sense of completion.

In Illalla istun sohvalle ja luen kirjaa…, the focus is on the activity of reading in the evening, not on finishing a specific book, so the partitive kirjaa is the natural choice.

What does lattialampun vieressä literally mean, and why is lattialampun in the genitive?

Breakdown:

lattialamppu – floor lamp (compound: lattia “floor” + lamppu “lamp”)
lattialampun – genitive singular of lattialamppu
vieressä – “next to, beside”

In Finnish, the word vieressä works like a postposition meaning “next to / beside”.
To say “next to X”, you usually use:

X:n vieressä – literally “in the next‑to of X”

So:

lattialampun vieressä = “next to the floor lamp”

Lattialampun is genitive because vieressä (like many postpositions) requires its complement to be in the genitive: jonkin vieressä = “next to something”.

What is olevan in lattialampun vieressä olevan sohvapöydän?

Oleva is the present active participle of the verb olla (“to be”).
Oleva roughly means “being” or “that is”.

In the phrase:

lattialampun vieressä oleva sohvapöytä

you can understand it as:

“the coffee table that is next to the floor lamp”

Now, in your full sentence, that “coffee table” is part of the expression sohvapöydän ääressä (“at the coffee table”), where sohvapöydän must be in the genitive because of ääressä (see below). When the head noun goes to genitive, its agreeing participle also goes to genitive:

nominative: lattialampun vieressä oleva sohvapöytä
genitive: lattialampun vieressä olevan sohvapöydän

So olevan is simply oleva in the genitive case, agreeing with sohvapöydän.
Functionally, lattialampun vieressä olevan sohvapöydän = “of the coffee table that is next to the floor lamp”.

What does sohvapöydän ääressä mean? How is ääressä different from just saying sohvapöydällä?

Breakdown:

sohvapöydän – genitive of sohvapöytä (“coffee table”)
ääressä – postposition meaning “at, by (the side/edge of)”

Pöydän ääressä is a very common phrase meaning “at the table” in the sense of sitting/standing by it, usually for some activity (eating, reading, working, etc.):

syön pöydän ääressä – I eat at the table
istun työpöydän ääressä – I sit at my desk

So sohvapöydän ääressä means “at the coffee table / by the coffee table (sitting next to it)”.

Compare with:

sohvapöydällä – “on the coffee table” (something is physically on its surface)

So:

ääressä → by the table, at its side (typical for where a person sits)
-lla/-llä → on the table, on top of it

Why are olevan and sohvapöydän both in the genitive?

Inside a noun phrase, modifiers agree in case with the head noun.
The structure here is:

[lattialampun vieressä olevan sohvapöydän] ääressä

Because ääressä is a postposition that takes its complement in the genitive, the head noun sohvapöytä must be genitive:

sohvapöydän ääressä – at the coffee table

All the modifiers of sohvapöytä inside the same noun phrase then also appear in the genitive:

(lattialampun) vieressä – “next to the floor lamp”
oleva → olevan (genitive, agreeing with sohvapöydän)
sohvapöytä → sohvapöydän

So genitive spreads to the whole phrase:

nominative NP: lattialampun vieressä oleva sohvapöytä
genitive NP: lattialampun vieressä olevan sohvapöydän

This is a general rule: adjectives and participles inside a noun phrase usually take the same case as the noun they modify.

Can the long phrase lattialampun vieressä olevan sohvapöydän ääressä be said in a simpler way?

Yes, you can rephrase it more simply, at the cost of some compactness. For example:

Split the information into two parts:
- Illalla istun sohvalle ja luen kirjaa *sohvapöydän ääressä lattialampun vieressä.*
  (“…at the coffee table, next to the floor lamp.”)
Use a relative clause instead of a participle:
- …luen kirjaa *sohvapöydän ääressä, joka on lattialampun vieressä.
  (“…at the coffee table *which is next to the floor lamp.”)

The original participle construction:

lattialampun vieressä olevan sohvapöydän ääressä

is very natural Finnish and quite typical in written style, but as a learner you can safely use the clearer relative clause version until you’re more comfortable with participles.

What are lattialamppu and sohvapöytä exactly? Why are they written as one word?

Both are compound nouns:

lattia (floor) + lamppu (lamp) → lattialamppu (floor lamp)
sohva (sofa) + pöytä (table) → sohvapöytä (coffee table / sofa table)

In Finnish, such noun–noun compounds are usually written as one word, not with a space. The case ending is added only to the last part of the compound:

lattialamppu → lattialampun (genitive)
sohvapöytä → sohvapöydän (genitive)

So lattialampun vieressä = “next to the floor lamp”, and sohvapöydän ääressä = “at the coffee table”.

Why are istun and luen in the present tense if we talk about the evening (possibly in the future)?

Finnish often uses the present tense for future events when there is a time expression that makes the time clear:

Huomenna menen töihin aikaisin. – “Tomorrow I will go to work early.”
Illalla istun sohvalle ja luen kirjaa… – “In the evening I will sit on the sofa and read a book…”

So istun and luen are morphologically present tense, but with Illalla they naturally refer to what you do (or typically do) in the evening, including future evenings. Finnish doesn’t need a separate future tense form here.