Tiivistämme vanhan ikkunan.

The dictionary form is tiivistää.

Tiivistämme = tiivistä- + -mme

• tiivistä- = the verb stem
• -mme = we

So tiivistämme is the 1st person plural present tense form: we seal / we weatherstrip / we make tight.

The ending -mme marks the subject we.

So Finnish often does not need a separate word for we:

• Tiivistämme vanhan ikkunan. = We seal the old window.
• Me tiivistämme vanhan ikkunan. = also We seal the old window, but me is now stated explicitly.

The pronoun me is often left out because the verb ending already tells you who is doing the action.

Because Finnish verbs usually already show the subject.

In English, you must say we seal.
In Finnish, tiivistämme already contains we.

If you add me, it usually gives extra emphasis, contrast, or clarity:

• Me tiivistämme vanhan ikkunan, he korjaavat oven.
  We seal the old window, they repair the door.

Without that kind of contrast, leaving me out is completely normal.

Because vanhan ikkunan is a noun phrase, and in Finnish the adjective must agree with the noun.

The basic forms are:

• vanha = old
• ikkuna = window

Here they appear as:

• vanhan
• ikkunan

Both get the same case ending pattern because they belong together: old window.

In this sentence, that phrase is the object of the verb, and it is treated as a whole/complete object. That is why you see this -n form.

This is a very common question.

Formally, ikkunan looks exactly like the genitive singular form of ikkuna. But in this sentence, its job is not to show possession. Its job is to mark the object.

So functionally, it is the object of the sentence: the old window is what is being sealed.

Many learner explanations say something like:

• in an affirmative sentence,
• a singular total object
• often looks like the genitive form

So ikkunan here is best understood as an object form, even though it looks like genitive.

Because vanhan ikkunan presents the object as a whole, not just an ongoing or incomplete amount of it.

Finnish often contrasts:

• total object → the action is seen as reaching the whole object / having a complete result
• partitive object → the action is ongoing, incomplete, or only affects part of something

So:

• Tiivistämme vanhan ikkunan.
  We are sealing the whole old window / we will finish sealing it.

Compare with:

• Tiivistämme vanhaa ikkunaa.
  We are sealing the old window with more focus on the ongoing process, not the completed result.

This is one of the key object-case contrasts in Finnish.

Yes. Finnish does not have a separate future tense in the same way English does.

So the present tense can mean:

• we seal
• we are sealing
• we will seal

Context tells you which one is meant.

For example:

• Tiivistämme vanhan ikkunan nyt. = We are sealing the old window now.
• Tiivistämme vanhan ikkunan huomenna. = We will seal the old window tomorrow.

So tiivistämme is grammatically present tense, but it can refer to the future too.

Because Finnish has no articles.

English distinguishes:

• a window
• the window

Finnish does not do this with separate words. Instead, definiteness is understood from context.

So vanha ikkuna can mean:

• an old window
• the old window

depending on the situation.

In your sentence, English may naturally use the old window, but Finnish itself does not have a separate word corresponding to the.

The neutral order here is very natural:

• Tiivistämme vanhan ikkunan.

If you include the subject pronoun, the neutral full sentence would be:

• Me tiivistämme vanhan ikkunan.

But Finnish word order is more flexible than English. You can move words for emphasis or contrast.

For example:

• Vanhan ikkunan tiivistämme ensin.
  The old window we’ll seal first.

That sounds more marked than the original sentence. So yes, the words can move, but the original order is the most neutral one.

Roughly like this:

TII-vis-täm-me

A few important points:

• tii has a long ii
• mm is a long consonant
• ä is a front vowel, somewhat like the a in cat, but cleaner and more Finnish-sounding
• stress is on the first syllable

Also remember that Finnish spelling is very regular:

• double vowels are longer
• double consonants are longer

So in this sentence:

• tii in tiivistämme is long
• kk in ikkunan is long
• mm in tiivistämme is long