Learn Hardcore Finnish: Jos bussi on myöhässä, minä vaihdan raitiovaunuun. - If the bus is late, I change to the tram.

Kun bussi on myöhässä, minä vaihdan raitiovaunuun.
= When(ever) the bus is late, I change to the tram (this is what I usually do in that situation).

So jos = hypothetical/uncertain, kun = real/whenever/when (more certain).

Why is there a comma after myöhässä?

The sentence has two clauses:

Jos bussi on myöhässä – the conditional (subordinate) clause
minä vaihdan raitiovaunuun – the main clause

In standard Finnish, when a jos-clause (or other subordinate clause) comes first, it is followed by a comma:

Jos bussi on myöhässä, minä vaihdan raitiovaunuun.

If you reverse the order, you usually don’t use a comma before jos:

Minä vaihdan raitiovaunuun jos bussi on myöhässä.

Why is the present tense (on, vaihdan) used even though this is about the future?

Finnish normally uses the present tense to talk about the future when the context makes the time clear:

Jos bussi on myöhässä, minä vaihdan raitiovaunuun.
Literally: If the bus is late, I change to the tram.
Naturally in English: If the bus is late, I’ll change to the tram.

There is no separate “will” form like in English. Time is understood from context, adverbs, or other information, not from a special future tense.

What exactly does bussi on myöhässä mean, and why not a simple adjective?

Bussi on myöhässä is an idiomatic expression meaning:

The bus is late (behind schedule).

Finnish often uses olla + an adverbial form instead of a plain adjective:

olla myöhässä = to be late (in the sense of behind schedule)
Bussi on myöhässä. = The bus is late (arriving after the planned time).

You normally wouldn’t say bussi on myöhäinen for a late bus; olla myöhässä is the natural phrase.

What grammatical form is myöhässä, and what’s the difference between myöhässä and myöhään?

Myöhässä ends in -ssä, which is the inessive case. Here it functions as an adverbial form in the fixed expression olla myöhässä:

olla myöhässä = to be late / to run late

Myöhään is different:

myöhään = late in the sense of at a late hour
- Menin nukkumaan myöhään. = I went to bed late.

So:

bussi on myöhässä = the bus is late (behind schedule)
bussi tulee myöhään = the bus comes late (at a late time)

Is minä necessary here? Could you just say Jos bussi on myöhässä, vaihdan raitiovaunuun?

The pronoun minä is not necessary. The verb ending -n in vaihdan already shows that the subject is I:

Jos bussi on myöhässä, vaihdan raitiovaunuun. – completely correct.

Including minä usually adds:

emphasis (contrasting with someone else: I will do this) or
clarity (for beginners or in spoken language when stressing the subject).

So both are fine; the version without minä is more typical in neutral written Finnish.

What does vaihdan raitiovaunuun literally mean, and how does vaihtaa work with transport?

Vaihdan raitiovaunuun literally:

vaihdan = I change / I switch
raitiovaunuun = to the tram (illative case, “into/to the tram”)

With means of transport, vaihtaa is often used like this:

vaihtaa + mihin? (illative) = to change to what?
- vaihdan junaan = I change to the train
- vaihdan bussiin = I change to a bus
- vaihdan raitiovaunuun = I change to the tram

It does not mean “I replace the tram” here; it means you switch from one mode of transport to another.

Why is it raitiovaunuun, not just raitiovaunu?

Raitiovaunuun is in the illative case, which often corresponds to “to / into” in English.

For words ending in a vowel, the illative is formed by:

lengthening the final vowel and adding -n
- talo → taloon (into the house)
- koulu → kouluun (to school)
- raitiovaunu → raitiovaunuun (to the tram)

So raitiovaunuun literally means “into/to the tram”, which is why it’s used after vaihdan (I change to).

Could you say Minä vaihdan raitiovaunun instead? What would that mean?

Minä vaihdan raitiovaunun would be understood as:

I change the tram / I replace the tram (the tram is the object being changed).

That’s a different meaning. In the original sentence, raitiovaunuun is not an object but a destination (illative case):

vaihdan raitiovaunuun = I change to the tram (I myself move to that vehicle/mode)
vaihdan raitiovaunun = I change the tram (I do something to the tram)

So for switching transport, you need the illative: mihin? → raitiovaunuun.

Is there a more colloquial way to say raitiovaunuun?

Yes. In everyday spoken Finnish, people often use ratikka instead of raitiovaunu:

Jos bussi on myöhässä, vaihdan ratikkaan.

Here ratikkaan is also illative (mihin? “to what?”).
Raitiovaunu is more formal/standard; ratikka is very common in speech, especially in cities with trams.

Why do we need on in bussi on myöhässä? Can you drop it like in English “bus late”?

You normally must use the verb olla (on) in a full Finnish sentence like this:

Bussi on myöhässä. = The bus is late.

Leaving out on would sound like an unfinished phrase, not a complete sentence.

In headlines, notes, or very telegraphic language you might sometimes see verbs omitted, but in normal Finnish grammar, the copula verb olla is required here.

Is the word order fixed, or can I move the parts around?

The basic word order is:

Jos bussi on myöhässä, minä vaihdan raitiovaunuun.

You can also say:

Minä vaihdan raitiovaunuun, jos bussi on myöhässä.
(Comma here is optional and often omitted: Minä vaihdan raitiovaunuun jos bussi on myöhässä.)

Other orders are possible but change emphasis and may sound marked or poetic, for example:

Raitiovaunuun minä vaihdan, jos bussi on myöhässä.
(emphasis on to the tram)

For most situations, stick to the original two variants.