Learn Hardcore Finnish: Pieni vahinko liikenteessä voi riittää siihen, että poliisi pysäyttää auton. - A small accident in traffic can be enough for the police to stop the car.

Pieni vahinko liikenteessä – subject
- pieni = small (adjective, nominative singular)
- vahinko = accident / damage (noun, nominative singular)
- liikenteessä = in traffic (inessive case, location)
voi riittää – verb phrase
- voi = can / may (3rd person singular of voida)
- riittää = to be enough / to suffice (infinitive)
siihen, että poliisi pysäyttää auton – complement of riittää
- siihen = to that (illative of se, referring forward to the että‑clause)
- että poliisi pysäyttää auton = that the police stop the car (subordinate clause)

So the structure is basically:

[A small accident in traffic] [can be enough] [for it to happen that the police stop the car].

What case is liikenteessä, and what does it add to the meaning?

Liikenteessä is in the inessive case (ending -ssa/-ssä), which typically means in, inside, within.

liikenne = traffic
liikenteessä = in traffic

Here it tells you where the pieni vahinko (small accident / mishap) happens: not just any small accident, but specifically in traffic. So it’s like saying:

pieni vahinko liikenteessä ≈ a small accident (occurring) in traffic

Why is it pieni vahinko and not something like partitive pientä vahinkoa?

Pieni vahinko is in the nominative singular, which is the normal form for the subject of a sentence.

You might see partitive subjects (like pientä vahinkoa) in Finnish, but those are usually used when:

the action is incomplete, ongoing, or repeated, or
you are talking about an indefinite quantity of something uncountable.

Here, pieni vahinko is presented as a whole, countable event, in a general statement:

Pieni vahinko liikenteessä voi riittää…
A single, small mishap in traffic may be enough…

So nominative pieni vahinko fits better: it’s a generic, but still “whole” type of event, not a vague mass of “some small damage”.

What exactly does riittää siihen, että… mean, and why is siihen used?

The pattern riittää siihen, että… is a very common Finnish structure meaning:

to be enough for (something to happen)
to suffice so that…

Literally:

riittää = is enough
siihen = to that (illative of se)
että… = that…

So you can think of it as:

riittää siihen, että X ≈ is enough for it that X happens
→ more natural English: is enough for X to happen

Why siihen?
In Finnish, riittää often takes a complement in a case like the illative (-een, into/to):

Raha riittää siihen, että ostan auton.
The money is enough for me to buy a car.

Here, siihen is a pronoun pointing forward to the whole että‑clause:

siihen, että poliisi pysäyttää auton
= for (the fact) that the police stop the car

What is the role of että here? Is it like English “that”?

Yes. Että introduces a subordinate clause, very much like English that in phrases like:

that the police stop the car
that he comes early

In the sentence:

…siihen, että poliisi pysäyttää auton.

the että‑clause että poliisi pysäyttää auton works as the content or result that is “enough”:

voi riittää siihen, että poliisi pysäyttää auton
can be enough (for it) that the police stop the car
→ can be enough for the police to stop the car

Why is there a comma before että?

Finnish punctuation rules require a comma before most subordinate clauses, including those introduced by että, regardless of whether you’d put a comma there in English.

So:

…riittää siihen, että poliisi pysäyttää auton.

is standard because että poliisi pysäyttää auton is a dependent clause; Finnish orthography almost always separates such clauses with a comma.

In English we don’t usually write a comma before “that” in this type of sentence, but in Finnish you do.

Why is it poliisi (singular) and not something like “the police” in plural?

In Finnish, poliisi is:

both the profession noun: a police officer
and can also refer collectively to the police as an authority

In this sentence:

että poliisi pysäyttää auton

the singular poliisi refers to the police as an institution / authority or to a typical officer in a generic way. It’s understood as:

that the police stop the car
or
that a police officer stops the car (in general, not a specific one)

If you said poliisit pysäyttävät auton, that would sound more like the police officers (plural, specific group) stop the car, which is a bit less generic.

Why is auton in the form with -n? What case is that and what does it mean here?

Auton is the genitive form of auto (car):

auto = car (nominative)
auton = car’s / the car (genitive)

However, in Finnish, the genitive singular is also used as the “total object” form for many verbs, including pysäyttää.

So:

pysäyttää auton = to stop the car (completely / as a whole)

This is not about possession here; it’s about the object case:

Hän pysäyttää auton.
He/She stops the car. (complete event → genitive object)

If the object were partial or incomplete, Finnish could use the partitive instead, but with pysäyttää and a whole, definite car, auton is the normal object form.

What’s the difference between pysäyttää and pysähtyä?

These are a classic Finnish transitive/intransitive verb pair:

pysäyttää = to stop something (transitive – takes an object)
- Poliisi pysäyttää auton.
  The police stop the car.
pysähtyä = to stop (oneself) / come to a stop (intransitive – no object)
- Auto pysähtyy.
  The car stops.

In the sentence:

että poliisi pysäyttää auton

the police are actively causing the car to stop, so the transitive verb pysäyttää with object auton is used.

What does vahinko mean here? How is it different from onnettomuus?

Both vahinko and onnettomuus can relate to unfortunate events, but they’re not identical:

vahinko
- basic meanings: damage, harm, mishap, (in some contexts) accident
- often something smaller, a minor mistake or minor damage
- can be used for both physical damage and abstract “harm”
onnettomuus
- typically: accident in the sense of a traffic accident, serious incident
- usually sounds more serious, like collisions, crashes, etc.

In pieni vahinko liikenteessä, the idea is more like:

a small mishap / minor accident in traffic — maybe a little bump, a small violation, or some minor incident

If you said pieni onnettomuus liikenteessä, it would sound more like a small-scale traffic accident (still more “accident-ish” and event-like than vahinko).

Could the word order be changed? For example, can poliisi come earlier in the sentence?

Finnish word order is quite flexible, but changes in order tend to change emphasis.

Original:

Pieni vahinko liikenteessä voi riittää siihen, että poliisi pysäyttää auton.

Some possible variants:

Liikenteessä pieni vahinko voi riittää siihen, että poliisi pysäyttää auton.
– Emphasises the traffic context first: In traffic, a small accident may be enough…
Pieni vahinko liikenteessä voi riittää, jotta poliisi pysäyttää auton.
– Uses jotta instead of että; still understandable, but jotta usually emphasizes purpose/result a bit more deliberately.

Bringing poliisi very early, like:

Poliisi voi pysäyttää auton, jos liikenteessä tapahtuu pieni vahinko.

is a rephrasing, not just word-order change: now you explicitly say if a small accident happens… instead of using the riittää siihen, että structure. The meaning is similar, but the grammar is different.

The original word order is natural and neutral in standard written Finnish.