Learn Hardcore Finnish: Lauantaina käymme koko perheen kanssa uimahallissa. - On Saturday we go with the whole family to the swimming hall.

Finnish usually does not use a separate preposition like English on with days of the week. Instead, the case ending on the noun expresses that meaning.

English: on Saturday
Finnish: lauantaina (no extra word needed)

The role of on is encoded in the -na ending:

on Monday → maanantaina
on Friday evenings → perjantai‑iltaisin (here another type of time-form, but again no preposition)

Where is the pronoun we in käymme? Why is there no separate word for we?

In Finnish, the personal ending on the verb usually shows the subject, so the separate pronoun can be left out.

Verb: käymme
- dictionary form: käydä (to go visit / to pop in / to attend)
- stem: käy-
- -mme = ending for we (1st person plural)

So käymme means we go / we visit / we attend.

You can add the pronoun me for emphasis or clarity:

Me käymme koko perheen kanssa uimahallissa.
= We (as opposed to someone else) go to the swimming hall with the whole family.

But in neutral sentences where the subject is clear from context, Finns usually omit me, and just say käymme.

What is the difference between käymme and menemme in this kind of sentence?

Both can translate to we go, but they have different nuances:

mennä → menemme
- basic idea: movement from one place to another (to go somewhere)
- focus is on the act of going / moving
käydä → käymme
- basic idea: to go (somewhere) and then come back; to visit / attend / pop by
- often suggests a more or less complete visit

In this sentence:

Lauantaina käymme koko perheen kanssa uimahallissa.
→ Emphasis: we go there as a visit / outing (and naturally return).

If you say:

Lauantaina menemme koko perheen kanssa uimahalliin.

it sounds more like you are focusing on the movement going to the swimming hall. Both are correct, but käydä + inessive (-ssa) is a very common pattern for regular visits:

Käymme uimahallissa joka viikko.
We (regularly) go to the swimming hall.

What does koko perheen kanssa literally mean, and how is it structured?

koko perheen kanssa means with the whole family.

Breakdown:

koko = whole, entire
perhe = family (dictionary form)
perheen = family in genitive singular (of the family)
kanssa = with

So literally:

koko perheen = of the whole family
kanssa = with
→ together: with the whole family.

In Finnish, kanssa is a postposition (like a preposition, but it comes after the noun phrase), and it normally requires the noun in the genitive:

ystävä → ystävän kanssa = with a friend
lapset → lasten kanssa = with the children
äiti ja isä → äidin ja isän kanssa = with mother and father

Why is it perheen (genitive) and not perhe in nominative?

Because of kanssa.

The postposition kanssa (with) generally takes the noun (or noun phrase) in the genitive case:

perhe → perheen kanssa (with the family)
koko perhe → koko perheen kanssa (with the whole family)
ystävä → ystävän kanssa (with a friend)
opettaja → opettajan kanssa (with the teacher)

So perhe has to change to its genitive form perheen to agree with kanssa.

Is kanssa exactly the same as English with?

It is very close in meaning, but used a bit more narrowly.

kanssa is mainly:

with in the sense of together with someone or accompanied by someone:
- Tulen ystävän kanssa. = I will come with a friend.
- Asun vanhempieni kanssa. = I live with my parents.

It is not used for all the meanings of English with:

Instrument (cut with a knife):
- English: with a knife
- Finnish: veitsellä, using the adessive case, not veitsen kanssa.
Cause/feature (a girl with blue eyes):
- English: with blue eyes
- Finnish: sinisilmäinen tyttö (blue-eyed girl) or tyttö, jolla on siniset silmät, not tyttö sinisten silmien kanssa in normal language.

So in this sentence, koko perheen kanssa is the typical together with use, where kanssa fits perfectly as English with.

Why is uimahallissa in the -ssa form, and what does that ending mean?

uimahallissa means in/at the swimming hall.

Breakdown:

uimahalli = swimming hall, indoor swimming pool complex
- uima = related to swimming
- halli = hall
uimahallissa = in the inessive case:
- ending -ssa / -ssä = in, inside, at

So uimahallissa literally means in the swimming hall.

With the verb käydä (to visit / to go and come back), Finnish typically uses a static location case (inessive):

Käyn kirjastossa. = I go to the library (and visit it).
Käymme kaupassa. = We go to the shop.
Käyn uimahallissa. = I go to the swimming hall.

That is why the sentence uses uimahallissa with käymme.

Could we say uimahalliin instead of uimahallissa? What is the difference?

Yes, uimahalliin is also a correct form, but it changes the nuance.

uimahallissa (inessive -ssa / -ssä)
- basic meaning: in / at the swimming hall
- used with käydä to talk about visiting a place
uimahalliin (illative -in / -hin / -seen etc.)
- basic meaning: into / to the swimming hall
- direction towards the place

Compare:

Lauantaina käymme uimahallissa.
= On Saturday we (will) go to the swimming hall (visit it).
Lauantaina menemme uimahalliin.
= On Saturday we (will) go to the swimming hall (focusing on going there).

So:

käydä + inessive (-ssa) is the usual pattern for go (and visit) somewhere.
mennä + illative (-in) is the usual pattern for go to somewhere (direction).

What is the difference between uimahalli and just uima-allas or uimala?

These words all relate to swimming, but they are not identical:

uimahalli
- an indoor swimming hall/pool complex
- usually a public building with pools, showers, saunas, etc.
uima-allas
- a (single) swimming pool or basin itself
- could be indoor or outdoor, public or private
uimala
- a swimming facility or bathing place
- can be outdoor (for example a beach or outdoor pool area), sometimes also general for swimming place

In the sentence, uimahallissa clearly means an indoor public facility for swimming, like a leisure center or municipal pool hall.

Can I change the word order, for example: Käymme lauantaina koko perheen kanssa uimahallissa? Is that still correct?

Yes, that word order is also correct.

Finnish word order is relatively flexible, and elements can be rearranged to change emphasis, not basic meaning.

Some possible orders:

Lauantaina käymme koko perheen kanssa uimahallissa.
– Neutral; mild emphasis on when.
Käymme lauantaina koko perheen kanssa uimahallissa.
– Neutral; mild emphasis on we go (as an activity) first.
Koko perheen kanssa käymme lauantaina uimahallissa.
– More emphasis on with the whole family.

All are grammatical. The most typical neutral choices here would be 1 or 2.

How would I say this in the past tense, or to clearly talk about future?

Finnish often uses the present tense for future events, especially when there is a time expression (like lauantaina) that makes the future meaning clear:

Lauantaina käymme uimahallissa.
= On Saturday we will go to the swimming hall.

To talk about the past (we went), you use the past tense (imperfect):

Kävimme lauantaina koko perheen kanssa uimahallissa.
= We went to the swimming hall with the whole family on Saturday.

Future:

There is no separate future tense; present tense + time expression is normal:
- Huomenna käymme uimahallissa. = Tomorrow we will go to the swimming hall.
- Ensi viikolla käymme taas uimahallissa. = Next week we will go to the swimming hall again.

What is the role of koko in koko perheen kanssa, and how is it different from kaikki?

koko and kaikki both relate to all / whole, but they are used differently.

koko:

used with a singular noun to mean the whole / entire X:
- koko perhe = the whole family
- koko päivä = the whole day
- koko kirja = the whole book

kaikki:

can mean all (of them) or everyone / everything:
- kaikki perheenjäsenet = all family members
- kaikki lapset = all the children
- Kaikki tulevat. = Everyone is coming.

So:

koko perheen kanssa = with the whole family (as a group)
kaikkien perheenjäsenten kanssa = with all the family members (more explicit, plural individuals)

In this sentence, koko is natural because perhe is treated as one unit.