Learn Hardcore Finnish: Kun luen tekstiä, yritän arvata sanan merkityksen ennen kuin katson sanakirjaa. - When I read a text, I try to guess the meaning of the word before I look at a dictionary.

Unspecified / ongoing amount of text
You are not talking about one specific, complete text (like one whole article or one document), but about reading text in general, some amount of text. Finnish often uses the partitive for:
- an unspecified amount: luen tekstiä = I read (some) text
- mass-like or unbounded objects.
Process-like action
With verbs describing an ongoing process, the object often appears in the partitive, because the action is not presented as completed on a clear, bounded object.

If you used luen tekstin, it would suggest something like I read the text (from beginning to end), a specific, complete text.

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

Finnish usually drops personal pronouns when they are obvious from the verb ending.

luen = I read
yritän = I try
katson = I look

Each of these verb forms already contains the 1st person singular ending -n, so adding minä would be redundant in a neutral sentence. You can say Minä luen tekstiä, but in everyday Finnish, the pronoun is often omitted unless you want to:

emphasize the subject (Minä yritän, en sinä)
contrast with someone else
or avoid ambiguity.

What exactly does kun do at the beginning of the sentence, and why is there a comma?

Kun is a subordinating conjunction meaning when (in the sense of whenever / at the time that). It introduces a subordinate clause:

Kun luen tekstiä = When I read text / Whenever I read text

This clause sets the circumstances under which the main action happens.

The part after the comma is the main clause:

yritän arvata sanan merkityksen ennen kuin katson sanakirjaa

Finnish punctuation here is similar to English: a comma is usually placed between a subordinate clause at the beginning and the following main clause.

What is the difference between kun and kuin here?

They look similar but work differently:

kun = when
- Introduces a time clause: Kun luen tekstiä…
kuin = often than or part of certain fixed conjunctions
- In this sentence it appears in ennen kuin = before (something happens).

So:

kun (alone) introduces the first time clause: Kun luen tekstiä
kuin (together with ennen) introduces the later time clause: ennen kuin katson sanakirjaa

You cannot swap them here; ennen kun is wrong in standard Finnish, and kun luen tekstiä cannot use kuin.

Why is it yritän arvata and not yritän arvaan or yritän arvaamaan?

The verb yrittää (to try) is commonly followed by the basic infinitive (the 1st infinitive):

yritän arvata = I try to guess

This pattern is similar to English try to do.

Why not the other forms?

yritän arvaan – wrong: Finnish does not use a finite verb after yritän in this way. You need the infinitive.
yritän arvaamaan – this is the 3rd infinitive in illative (-maan/-mään), which can be used with some verbs for going to do something or starting an activity, but yrittää normally doesn’t take that form in this meaning.

So the natural construction is yrittää + basic infinitive:

yritän oppia (I try to learn)
yritän muistaa (I try to remember)
yritän arvata (I try to guess)

Why is sanan in this form? What case is it, and what does it express?

Sanan is the genitive singular of sana (word).

Here it expresses possession / belonging:

sanan merkitys = the meaning of the word

In Finnish, this kind of “of” relationship (X of Y) is usually shown by putting Y in the genitive:

kirjan nimi = the name of the book
opettajan pöytä = the teacher’s table
sanan merkitys = the meaning of the word

So sanan tells you that the meaning we are talking about is the meaning of a word.

Why is merkityksen in the form with -n instead of the basic merkitys?

Merkityksen is also in the -n form, which in this function is usually called the total object (formally same as the genitive singular for nouns).

With verbs, Finnish distinguishes roughly between:

total object (often in -n or nominative): action is viewed as affecting the whole object, completed or bounded.
partitive object (-a/-ä): action is ongoing, incomplete, repeated, or affects only part of the object.

Arvata merkityksen presents the act of guessing as aimed at the whole meaning of the word, as a more complete target:

yritän arvata sanan merkityksen ≈ I try to guess the (full) meaning of the word.

That is why merkitys appears as merkityksen rather than bare merkitys.

Could we say yritän arvata sanan merkitystä instead of merkityksen? What would change?

Yes, merkitystä (partitive) is grammatically possible, but it changes the nuance.

yritän arvata sanan merkityksen
- Total object: you are trying to get the whole, definite meaning.
- Suggests a clearer, more goal-oriented attempt at the full meaning.
yritän arvata sanan merkitystä
- Partitive object: emphasizes the action as incomplete, tentative, or not reaching a fully defined result.
- Can sound like you are messing around with or partially guessing at the meaning, not necessarily succeeding or not targeting a fully definite meaning.

In many everyday contexts, both forms could occur, and the choice is about subtle aspectual nuance. The version with merkityksen is very natural here, because you normally try to figure out the full meaning of a word.

Why is sanakirjaa in the partitive instead of sanakirjan?

Sanakirjaa is the partitive singular of sanakirja (dictionary).

With katsoa (to look, watch), Finnish often uses the partitive object when:

you are describing simply looking at something in a general or ongoing way
the action is not seen as completed on a clearly bounded object.

Compare:

katson sanakirjaa = I look at the dictionary (some amount of looking; generic activity)
katson sanakirjan could be used in special contexts where you mean something like I check the whole dictionary (from cover to cover), which is unusual.

Also, in practice, for “look something up in the dictionary”, Finns actually prefer:

katsoa sanakirjasta (look from the dictionary / in the dictionary) – dictionary in the elative case.

So your sentence with katson sanakirjaa is fine and grammatical, but the most idiomatic “I look it up in the dictionary” would be something like:

…ennen kuin katson sen sanakirjasta.
(…before I look it up in the dictionary.)

Why are luen, yritän, and katson all in the present tense if we are talking about a general habit?

Finnish present tense covers both:

actions happening right now, and
habitual / general actions.

So:

Kun luen tekstiä = When I read text / Whenever I read text
yritän arvata… = I try to guess…
ennen kuin katson sanakirjaa = before I look at the dictionary

There is no separate “simple present” vs “present progressive” vs “habitual” tense in Finnish. The context and words like kun and ennen kuin make it clear this is a repeated, habitual situation.

Why do we use ennen kuin instead of just ennen before katson sanakirjaa?

Ennen by itself is a preposition/postposition meaning before, and it normally takes a noun (in the partitive):

ennen työpäivää = before the working day
ennen iltaa = before evening

When you want to say before followed by a full clause with a verb, you must use ennen kuin:

ennen kuin katson sanakirjaa = before I look at the dictionary
ennen kuin menen kotiin = before I go home

So the rule of thumb:

ennen + noun
ennen kuin + clause (with a finite verb)

Could we change the word order to Yritän arvata sanan merkityksen, kun luen tekstiä? Would the meaning change?

Yes, that word order is correct and natural:

Kun luen tekstiä, yritän arvata sanan merkityksen…
Yritän arvata sanan merkityksen, kun luen tekstiä…

Both describe the same situation: when you are reading text, you try to guess word meanings before using a dictionary.

The difference is mostly in emphasis:

Starting with Kun luen tekstiä foregrounds the situation (what happens when you read).
Starting with Yritän arvata sanan merkityksen foregrounds your strategy (what you try to do).

Grammatically and semantically, both are fine. The relationship between the clauses stays the same.