Learn Hardcore Finnish: Tiistai-iltaisin menen joogatunnille ystäväni kanssa. - On Tuesday evenings I go to a yoga class with my friend.

tiistai‑iltaisin = on Tuesday evenings (as a routine)
tiistai‑iltana = on Tuesday evening (this particular Tuesday evening, or one specific evening)

Compare:

Tiistai‑iltana menen elokuviin. = This Tuesday evening I’m going to the movies.
Tiistai‑iltaisin menen joogatunnille. = On Tuesday evenings I (normally) go to yoga class.

The ‑isin ending is also seen in:

öisin = at night(s), by night, at nights (habitually)
kesäisin = in summers / every summer
maanantai‑aamuisin = on Monday mornings (habitually)

Why is there a hyphen in tiistai‑iltaisin? Could it also be written as one word?

You’ll often see both styles, but here’s the logic.

Base expression:

tiistai‑ilta = Tuesday evening (literally Tuesday‑evening)

When you add the ‑isin ending, it attaches to the second part:

tiistai‑ilta
- ‑isin → tiistai‑iltaisin

The hyphen helps show the original compound tiistai‑ilta clearly. You may also see it written without a hyphen (especially in less formal contexts) as tiistai-iltaisin → tiistaiiltaisin, but the hyphenated form keeps it more readable.

Key point: Finnish loves compounds; the hyphen here is mainly about clarity, not a change in meaning.

Why is Tiistai capitalized here? Are weekday names always capitalized in Finnish like in English?

No. In Finnish, weekday names are normally NOT capitalized.

They are written in lower case:

maanantai = Monday
tiistai = Tuesday
keskiviikko = Wednesday
etc.

In your sentence, Tiistai‑iltaisin appears at the start of the sentence, so Tiistai‑ is capitalized only for that reason. If it were in the middle of a sentence, it would be:

Menin tiistai‑iltana elokuviin.

Why is the verb menen used here? Could I also say käyn?

Menen is the 1st person singular of mennä = to go (to some place).

Tiistai‑iltaisin menen joogatunnille.
= On Tuesday evenings I go (I go there) to yoga class.

You can also say:

Tiistai‑iltaisin käyn joogatunnilla.

Difference in nuance:

mennä + allative (‑lle) stresses the movement to something:
- menen joogatunnille = I go to the yoga class (I head there).
käydä + inessive (‑lla/‑llä) often expresses visiting / attending regularly:
- käyn joogatunnilla = I attend a yoga class / I go to yoga (as a regular activity).

In many everyday contexts, both are acceptable and the difference is subtle.
Your sentence chooses menen joogatunnille, which is perfectly natural Finnish.

Why is it joogatunnille and not just joogatunti or something like joogatunnilla?

Joogatunti is a compound:

jooga = yoga
tunti = hour / lesson → joogatunti = yoga class / yoga lesson

In joogatunnille, the word is in the allative case:

stem: joogatunti‑
allative ending: ‑lle
consonant gradation: tunti → tunnille (nt → nn in many forms) → joogatunnille = to a/the yoga class

Why allative ‑lle?

Verbs of physical motion (mennä, tulla, etc.) often use allative when going to an event, activity, or person:
- mennä tunnille = go to class
- mennä lääkärille = go to (the) doctor
- tulla luennolle = come to (the) lecture

Compare:

olen joogatunnilla (inessive ‑lla) = I am at / in a yoga class
menen joogatunnille (allative ‑lle) = I go to a yoga class

Why is joogatunti written as a single word in Finnish, not as two words like in English?

Finnish typically writes noun–noun combinations as one compound word when they form a single concept:

jooga + tunti → joogatunti (yoga class)
koulubussi (school bus)
työpäivä (work day)
kielikurssi (language course)

If you wrote jooga tunti as two separate words, it would sound like “yoga hour” in a more literal, non‑standard way, and not like the normal word for a “yoga class”.

So, when English uses a noun + noun phrase, Finnish very often fuses it into a compound noun.

What does ystäväni mean exactly, and why isn’t minun written separately?

Ystäväni means “my friend”.

Structure:

ystävä = friend
‑ni = 1st person singular possessive suffix = my → ystäväni = my friend

Finnish has two ways to express possession:

Possessive pronoun + noun
- minun ystäväni = my friend
Noun + possessive suffix
- ystäväni = my friend

Both are correct. In everyday speech and writing:

Using just the suffix (ystäväni) is very common and often feels more neutral.
Adding minun puts extra emphasis on whose friend it is:
- Minun ystäväni kanssa = with my friend (contrastive, e.g. not yours)

So ystäväni kanssa is the normal, unmarked way to say “with my friend”.

Why do we say ystäväni kanssa and not ystävän kanssa or kanssani?

These three forms all have slightly different meanings:

ystäväni kanssa
- ystäväni = my friend
- kanssa = with
  → with my friend (specific person)
ystävän kanssa
- ystävän = a friend / the friend (genitive)
- kanssa = with
  → with a friend / with the friend (no “my”)
kanssani
- kanssa
  - ‑ni = with me
    → with me

So:

ystäväni kanssa = with my friend
ystävän kanssa = with (a) friend (no possessor)
kanssani = with me

Your sentence needs “with my friend”, so ystäväni kanssa is the correct choice.

What case is ystäväni in when used with kanssa, and how does kanssa behave?

Kanssa is a postposition meaning “with”. It normally takes the genitive form of the noun:

ystävä (basic form)
ystävän kanssa = with (a) friend
- ystävän is genitive

When you add a possessive suffix, that form fills the same slot:

ystäväni kanssa = with my friend
(functionally “my‑friend‑GEN + kanssa”)

So:

Without possession: ystävän kanssa
With possession: ystäväni kanssa

You can think: “The genitive or a possessive‑suffixed form + kanssa”.

Why is there no Finnish word for “on” before tiistai‑iltaisin, like in English “on Tuesday evenings”?

Finnish usually does not use a preposition like “on” for days and many time expressions. Instead, the case ending on the time expression itself does the job.

Examples:

Tiistai‑iltaisin menen joogatunnille.
= (On) Tuesday evenings I go to yoga class.
Maanantaisin olen kotona.
= (On) Mondays I’m at home.
Viikonloppuna matkustan.
= (On) the weekend I travel.
Yöllä nukun.
= (At) night I sleep.

So tiistai‑iltaisin already encodes the meaning “on Tuesday evenings”; adding a separate word like English on isn’t needed.

Is the word order Tiistai‑iltaisin menen joogatunnille ystäväni kanssa fixed, or can it be changed?

Finnish word order is quite flexible. The basic neutral order here is:

[TIME] [VERB] [PLACE] [COMPANION]
Tiistai‑iltaisin menen joogatunnille ystäväni kanssa.

You can reorder elements to change emphasis, and many variants are grammatical:

Menen tiistai‑iltaisin joogatunnille ystäväni kanssa.
(More neutral; time after the verb.)
Tiistai‑iltaisin ystäväni kanssa menen joogatunnille.
(Emphasis on with my friend as part of the time frame.)
Ystäväni kanssa menen tiistai‑iltaisin joogatunnille.
(Emphasis on with my friend; “It’s with my friend that I go …”)

All mean essentially the same thing. The original order is very natural and typical for a simple statement of habit.

How would I say “On Tuesday evenings I go to yoga class with my friends” (plural friends)?

You need the plural possessive of ystävä:

ystävä = friend
plural stem: ystävä‑ → ystävi‑
genitive plural: ystävien
with 1st‑person possessive suffix: ystävieni = my friends

Then:

ystävieni kanssa = with my friends

Full sentence:

Tiistai‑iltaisin menen joogatunnille ystävieni kanssa.
= On Tuesday evenings I go to yoga class with my friends.

How would I say this sentence in the past tense, and how does mennä change?

To put it into the past (simple past / imperfect), change menen → menin:

mennä (to go)
- present 1sg: menen = I go
- past (imperfect) 1sg: menin = I went

So:

Tiistai‑iltaisin menin joogatunnille ystäväni kanssa.
= On Tuesday evenings I went to yoga class with my friend.

This describes a habitual action in the past (e.g. “When I lived there, on Tuesday evenings I used to go …”). The other words remain the same; only the verb changes tense.