Lukiessani tätä romaania ajattelen usein omaa elämääni.

Lukiessani means roughly “while I am reading” / “when I read”.

Grammatically, it is:

• the 3rd infinitive in the inessive case of lukea (“to read”) → lukiessa = “while (someone is) reading”
• plus the possessive suffix -ni = “my / I” → lukiessani = “while I am reading”

So structurally it’s luke-a → lukiessa + -ni = “while I’m reading”.
It functions like a time clause, similar to kun luen (“when I read”).

Finnish usually drops subject pronouns when the verb form already shows the person.

We know the subject is “I” from:

• ajattelen – 1st person singular (“I think”)
• -ni in lukiessani – the possessive suffix here marks the subject of the reading action as “I”

So minä would be redundant. You could say:

• Minä ajattelen usein omaa elämääni lukiessani tätä romaania.

but it sounds more emphatic or contrastive: I (as opposed to someone else) think about my life.

Tätä romaania is in the partitive case, not the genitive:

• tämä romaani (nom.) = this novel
• tämän romaanin (gen.) = of this novel / this novel (as a complete object)
• tätä romaania (part.) = this novel (as an ongoing, not completed object of an action)

With lukea (“to read”), the partitive object is used when the reading is in progress / not completed or when you talk about the activity in general.

So:

• Luen tätä romaania. = I’m (in the middle of) reading this novel.
• Luin tämän romaanin. = I read / finished this novel.

In our sentence, we are talking about the process of reading, not having finished it, so tätä romaania is natural.

The whole phrase tätä romaania is the object.

• tätä = “this” (partitive singular of tämä)
• romaania = “novel” (partitive singular of romaani)

They agree in case and number: both are partitive singular, forming one noun phrase: “this novel” as a partitive object of lukiessani (“while I am reading this novel”).

Because of the verb ajatella.

The basic pattern is:

• ajatella + partitive object = “to think (about) something”

Examples:

• Ajattelen sinua. = I think of you.
• Ajattelen tulevaisuutta. = I think about the future.

So here:

• omaa elämääni is in partitive singular → “my (own) life (as the thing I think about)”.

Nominative (oma elämäni) would be wrong here; ajatella normally requires the partitive for its object in this meaning.

There are two different things happening:

1. Agreement of the adjective

   • oma is an adjective (“own”).
   • In Finnish, adjectives agree in case and number with the noun:
     
     • omaa (partitive) + elämää (partitive).

2. Possessive suffix

   • -ni on elämääni marks “my” life.

So omaa elämääni literally is “(of) my own life” with:

• omaa – matching the noun in case
• elämääni – “my life” (life + partitive + my)

You could say just elämääni (“my life”) without omaa, but omaa adds emphasis: my *own life*, as opposed to someone else’s or life in general.

Yes, grammatically that’s fine:

• Lukiessani tätä romaania ajattelen usein elämääni.

That still means “I often think about my life.” (-ni on elämääni already shows “my”.)

Differences:

• elämääni – neutral “my life”
• omaa elämääni – slightly more personal / contrasted: my own life, my personal experiences as distinct from others’ lives or from life in general.

In natural Finnish, omaa elämääni is very common in this “reflect on my own life” type of context.

In the given sentence:

• Lukiessani tätä romaania ajattelen usein omaa elämääni.

usein comes before the object phrase. This is a very natural position.

Other acceptable positions (with slightly different emphasis) include:

• Ajattelen usein omaa elämääni lukiessani tätä romaania.
• Usein ajattelen omaa elämääni lukiessani tätä romaania.

What you normally don’t do is split the main verb and its subject (if expressed) in a strange way, or put usein deep inside the noun phrase. Adverbs like usein are fairly mobile, but they tend to sit close to the main verb they modify.

A very common and slightly more “basic learner-friendly” version would use kun + verb:

• Kun luen tätä romaania, ajattelen usein omaa elämääni.

This means essentially the same thing:

• Lukiessani tätä romaania… ≈ Kun luen tätä romaania…
  (“When I read this novel / While I am reading this novel…”)

The lukiessani construction is more compact and a bit more “written-language-like”, but it’s standard and very common.

In Finnish punctuation, participle constructions like lukiessani tätä romaania are usually not separated by a comma from the main clause when they share the same subject:

• Lukiessani tätä romaania ajattelen usein omaa elämääni. ✔

If you used a full kun-clause, then a comma is standard when the clause comes first:

• Kun luen tätä romaania, ajattelen usein omaa elämääni. ✔

So:

• kun + finite verb → usually comma
• lukiessani-type participle clause with same subject → usually no comma

The -ni specifically marks 1st person singular (“I / my”), so lukiessani always means “while I am reading”.

For other persons, you change the suffix:

• lukiessasi – while you (sg.) are reading
• lukiessaan – while he/she is reading
• lukiessamme – while we are reading
• lukiessanne – while you (pl.) are reading
• lukiessaan – while they are reading (same suffix as 3rd sg)

Without any suffix (lukiessa tätä romaania) the subject is unspecified / generic (“while reading this novel”), and usually understood from context (often the same as the subject of the main clause, but it’s less explicit).

They express different times relative to the reading:

• lukiessani tätä romaania

  • literally: “while (I am) reading this novel”
  • action of “thinking about my life” happens during the reading.

• luettuani tämän romaanin

  • from luettu (past participle of lukea) + -ani
  • literally: “after having read this novel” / “once I’ve read this novel”
  • action happens after finishing the novel.

So your sentence:

• Lukiessani tätä romaania ajattelen usein omaa elämääni.
  = While I’m in the process of reading, I often think about my own life.

Whereas:

• Luettuani tämän romaanin ajattelen usein omaa elämääni.
  = After I have read this novel, I often think about my own life.