Learn Hardcore Finnish: Illalla laitan villasukat jalkaan. - In the evening I put wool socks on my feet.

So the literal idea is “on the evening / at the evening”, but in English we say “in the evening”. The adessive -lla / -llä is often used for time expressions like this:

yöllä = at night
päivällä = in the daytime / in the day
kesällä = in (the) summer

Why is there no separate word for “in” in “Illalla”? Why isn’t it something like “in ilta”?

Finnish usually doesn’t use separate prepositions like in, on, at for time and place. Instead, it uses case endings on the noun.

English: in the evening
Finnish: illalla (ilta + -lla)

The ending -lla already contains the meaning of “in/at/on”, so you don’t add another word for “in”. Putting a separate word before ilta would be incorrect Finnish.

Why is it laitan and not just the dictionary form laittaa?

Laittaa is the infinitive form (the basic dictionary form), meaning “to put, to place, to set, to prepare (food), etc.”

In the sentence, the subject is I, so we need the 1st person singular present tense:

minä laitan = I put / I am putting
- minä = I
- laitan = I put (from laittaa)

Other forms for comparison:

sinä laitat = you put
hän laittaa = he/she puts
me laitamme = we put

So Illalla laitan… = “In the evening I put …”, or more naturally “In the evening I put on …”.

What exactly does laittaa mean here? Is it the same as “to wear” or “to dress”?

In this sentence laittaa has the meaning “to put (something somewhere / on something)”:

laittaa villasukat jalkaan = “to put woollen socks on (one’s feet)”

It is not “to wear” in general (that’s more like pitää yllään, olla jalassa / olla päällä) and not exactly “to dress (someone)” (that’s pukea).

Compare:

Laitan kirjan pöydälle. = I put the book on the table.
Laitan takin päälle. = I put on a coat.
Puen takin. = I dress (myself with) a coat / I put on a coat.

So here laitan = “(I) put on”.

Why is villasukat written as one word and not villa sukat?

Villasukat is a compound noun:

villa = wool
sukat = socks (plural of sukka)
villasukat = woollen socks / wool socks

In Finnish, when a noun (or adjective-like element) describes what kind of thing something is, it is very often written as one word:

villapaita = wool sweater (villa + paita)
aurinkolasit = sunglasses (aurinko + lasit)
talvikengät = winter shoes (talvi + kengät)

So villa sukat as two words is wrong in standard Finnish here; it should be villasukat.

Why is villasukat in the nominative plural (ending -t) and not in some other case?

Villasukat is the object of the verb laitan (“I put”). Finnish marks objects differently depending on things like completeness of the action.

Here, the idea is:

I put the socks fully on.
The action is complete, not partial or ongoing in a “halfway” sense.

For a complete object in the plural, Finnish usually uses nominative plural (ending -t):

Minä syön omenat. = I eat the apples (I eat them all).
Illalla laitan villasukat jalkaan. = In the evening I put (on) the woollen socks.

If the action were incomplete or “some amount of socks”, you could have a partitive, but that would sound strange here. So nominative plural villasukat is the normal choice for “I put the socks on (completely)”.

Why is jalkaan in the singular, when I have two feet?

This is one of those idiomatic patterns in Finnish. Jalka = foot/leg, and jalkaan is:

jalka (foot/leg) + -an (illative case, “into / onto”)
jalkaan = onto (the) foot

In many everyday expressions with clothes and body parts, Finnish often uses the singular, even though in reality there are two:

kengät jalkaan = put (your) shoes on (feet)
sukat jalkaan = put (your) socks on
hanskat käteen = put (your) gloves on your hand(s)

You can say jalkoihin (plural “onto the feet”), e.g. villasukat jalkoihin, and it’s correct, but jalkaan is more common and idiomatic in this particular phrase.

What case is jalkaan, and what does that case usually mean?

Jalkaan is the illative case of jalka.

jalka (basic form)
jalkaan (illative singular)

The illative case (typically endings -an, -en, -in, -seen) expresses movement into or onto something, like English “into, onto, to”:

kotiin = (to) home
kauppaan = into the shop
pöydälle (actually allative, but similar idea) = onto the table
jalkaan = onto the foot

So villasukat jalkaan = “woollen socks onto (the) foot” → “put (my) woollen socks on (my) feet”.

Where is the word “my”? Why doesn’t the sentence say “my feet” or “my socks”?

Possession with body parts and clothes is often understood from context in Finnish, so you don’t need to say “my” explicitly.

Illalla laitan villasukat jalkaan.
→ It’s naturally understood as my socks and my feet.

If you really want to mark possession, you can:

Use a possessive suffix:
- Illalla laitan villasukat jalkaani. = …onto my foot/feet.
Or add a pronoun (more emphatic, sometimes a bit heavy in simple sentences):
- Illalla laitan villasukat minun jalkoihini.

But in normal speech, just villasukat jalkaan is the most natural.

Why is there no word like “on” for “on my feet”? Where is that “on” hidden in the Finnish sentence?

The idea of “on (my feet)” is expressed by the case ending on jalkaan.

jalka = foot/leg
jalkaan = onto the foot → “on(to) the foot”

So instead of:

English: put socks on my feet
Finnish: laitan villasukat jalkaan

The preposition on is built into the word through the illative ending. Finnish generally prefers case endings over separate prepositions like “on, in, to, into”.

Can I change the word order, like “Illalla laitan jalkaan villasukat”?

Yes. Finnish word order is fairly flexible, especially with known information.

Both of these are grammatical:

Illalla laitan villasukat jalkaan. (neutral)
Illalla laitan jalkaan villasukat. (slightly more emphasis on villasukat at the end)

The most typical neutral order is:

[time] + [verb] + [object] + [place/direction]
→ Illalla laitan villasukat jalkaan.

Changing the order often changes emphasis more than meaning.

How would I say “In the evenings I put woollen socks on (my feet)” as a repeated habit?

For a habitual / repeated action (“in the evenings, usually, every evening”), Finnish commonly uses:

iltaisin = in the evenings / evenings, as a habit

So you could say:

Iltaisin laitan villasukat jalkaan.
= In the evenings, I (usually) put woollen socks on.

You can also keep illalla and add an adverb meaning “always/usually”, but iltaisin by itself nicely expresses the habitual idea.

Could I use pukea instead of laittaa? For example, “Illalla puen villasukat jalkaan”?

Yes, that’s possible and correct:

Illalla puen villasukat jalkaan.
= In the evening I put on woollen socks.

Pukea means “to dress (someone / oneself), to put clothes on”. With pukea, you often see:

Puen paidan päälle. = I put on a shirt.
Puen lapsen. = I dress the child.

The version with laittaa is slightly more neutral and very common in everyday speech for putting clothes on:

laittaa villasukat jalkaan
laittaa takki päälle

Both are good, natural Finnish; laittaa is just a bit more generic.