Pyyhin kyyneleen pois, koska elokuvan loppu on surullinen.

It can be either, depending on context.

With the verb pyyhkiä, the minä form pyyhin can be ambiguous between present and past. So this sentence could be understood as:

• I wipe away a tear, because the ending of the movie is sad
• or I wiped away a tear, because the ending of the movie is sad

Usually the surrounding context tells you which one is meant. Finnish often allows this kind of ambiguity when the situation makes the time clear.

Because Finnish usually leaves out subject pronouns when the verb ending already shows the person.

Here, pyyhin ends in -n, which tells you the subject is I. So minä is not necessary.

You could say Minä pyyhin kyyneleen pois..., but that would usually add emphasis, contrast, or a slightly less neutral tone.

Because kyyneleen is the object form used here.

In an affirmative finite sentence, a complete singular object is often in the genitive form. This is called the total object. The idea is that the action affects the whole object:

• Pyyhin kyyneleen pois = I wipe away the whole tear / a tear completely

The basic dictionary form is kyynel. Its form changes in other cases:

• kyynel = tear
• kyyneleen = of a tear / a tear as a total object
• kyyneltä = partitive singular
• kyyneleet = tears

So this is both a case issue and a stem-change issue.

Because kyyneltä would be the partitive, and that would suggest an incomplete, ongoing, or not fully bounded action.

Here the sentence presents the tear as a complete object being wiped away, so Finnish uses the total object:

• kyyneleen = a/the tear, as a complete object

If you used the partitive, it would sound less natural here. With tears, the partitive is more natural in the plural:

• Pyyhin kyyneliä pois = I wipe away tears / I am wiping away some tears

So kyyneleen fits the idea best in this sentence.

Pois adds the idea of away, off, or out of the way.

So:

• pyyhkiä = to wipe
• pyyhkiä pois = to wipe away / wipe off / remove by wiping

It works a bit like an English phrasal verb. The sentence is not just about wiping in general, but about wiping the tear away.

Because in Finnish, words like pois are often separate particles, not attached to the verb as one fixed written unit.

So pyyhkiä pois behaves a bit like a multi-word verb, but the parts can be separated by other sentence elements:

• Pyyhin kyyneleen pois
• Pyyhin pois kyyneleen

Both are possible. The first one is very natural here.

This is different from English, where learners often expect the verb and particle to stay together more rigidly.

Because loppu often takes a noun before it in the genitive to show what something is the end of.

So:

• elokuva = movie
• elokuvan loppu = the ending of the movie / the movie’s ending

This -n on elokuvan does not mean it is the object. It is just the normal way to say the end of something.

You can think of it as similar to English of the movie or the movie’s.

They mean different things:

• elokuvan loppu = the ending of the movie
• elokuvan lopussa = at the end of the movie

In this sentence, the ending itself is the subject of on surullinen, so you need loppu, not lopussa.

Compare:

• Elokuvan loppu on surullinen = The ending of the movie is sad
• Elokuvan lopussa kaikki kuolevat = At the end of the movie, everyone dies

So loppu names the ending, while lopussa gives a location in time or structure.

Because surullinen is a predicate adjective agreeing with the subject loppu.

Here:

• loppu is singular nominative
• so the adjective is also singular nominative: surullinen

That is the normal pattern after olla when you describe the subject:

• Loppu on surullinen = The ending is sad

Surullista would be used in a different kind of structure, for example:

• On surullista, että elokuvan loppu on tällainen = It is sad that the movie ends like this

So in your sentence, surullinen is the correct form.

Because koska introduces a subordinate clause, and in Finnish that clause is normally separated with a comma when it follows the main clause.

So:

• Pyyhin kyyneleen pois, koska elokuvan loppu on surullinen.

That comma is standard Finnish punctuation.

Yes. Finnish word order is fairly flexible, although some versions sound more natural than others.

Your sentence:

• Pyyhin kyyneleen pois, koska elokuvan loppu on surullinen.

is a very natural neutral order.

You could also hear:

• Pyyhin pois kyyneleen...

That is possible too, but the focus or rhythm changes a little. Finnish often moves words around for emphasis, information structure, or style, not because the grammar changes completely.

Because the speaker is presenting the ending as a current fact or a generally true description.

Even if pyyhin is understood as past, Finnish can still use present in the koska clause if the statement is seen as still true:

• the ending is sad

If you wanted to place that description fully in the past, you could also say:

• koska elokuvan loppu oli surullinen

So both can be possible, depending on how the speaker frames the situation.

Finnish has no articles.

So Finnish does not have separate words corresponding directly to English a, an, or the. That means forms like:

• kyyneleen
• elokuvan loppu

do not by themselves tell you exactly whether English should use a or the. That comes from context.

So kyyneleen could correspond to a tear or the tear, and elokuvan loppu naturally corresponds to the ending of the movie.

There are a couple of useful possibilities:

• Pyyhin kyyneleet pois = I wipe away the tears / all the tears
• Pyyhin kyyneliä pois = I wipe away tears / I am wiping away some tears

The difference is the same total-object vs partitive distinction:

• kyyneleet = the tears as a complete set
• kyyneliä = some tears, or an ongoing/unbounded action

So your original sentence uses the singular total object kyyneleen because it is talking about one tear being wiped away.