Learn Hardcore Finnish: Perjantaina juhlimme ystäväni syntymäpäivää. - On Friday we celebrate my friend's birthday.

In Finnish you turn weekdays into time-of-day adverbs by using the essive case (–na/–nä).
• perjantai (Friday) → perjantaina (on Friday)
This tells us when something happens.

How exactly do you form the essive for all weekdays?

Take the stem of the weekday and add –na or –nä depending on vowel harmony.
• maanantai → maanantaina
• tiistai → tiistaina
• keskiviikko → keskiviikkona, etc.

Why does juhlimme sometimes mean “we celebrate” and other times “we celebrated”?

Finnish has only one simple tense (often called “present”), which covers present and future. The past tense also ends up looking identical here:
• Present 1 pl: juhli-mme → juhlimme (we celebrate / will celebrate)
• Past 1 pl: juhl-i-mme → juhlimme (we celebrated)
You rely on context or time words like perjantaina to know which is meant.

Why is syntymäpäivää in the partitive case?

Many Finnish verbs that involve events or activities, like juhlia (to celebrate), take a partitive object. The partitive often signals:
• an ongoing or incomplete action (“celebrating something”)
• the object of certain verbs that aren’t fully “consumed”
Hence syntymäpäivä (birthday) → syntymäpäivää when it’s the object of juhlimme.

How do you form the partitive of a compound noun like syntymäpäivä?

In Finnish compounds only the last element declines. Here the head is päivä (day), whose partitive is päivää. The first element syntymä (birth) stays unchanged.
Result: syntymä + päivää = syntymäpäivää.

Why is it ystäväni instead of ystävä?

ystäväni is “my friend.” Finnish usually shows possession with a suffix:
• ystävä = friend
• ystävä-ni = friend-my = my friend
You could also say minun ystäväni, but you keep the suffix or the pronoun, not both.

How do possessive suffixes work in Finnish?

You attach them to the noun that is owned. Common singular suffixes:
• –ni = my
• –si = your (sing.)
• –nsä = his/her
So kirja (book) → kirjani (my book), and ystävä → ystäväni (my friend).

Can I change the word order in this sentence?

Yes—Finnish has fairly free word order for emphasis. For example:
• Perjantaina juhlimme ystäväni syntymäpäivää. (Neutral)
• Ystäväni syntymäpäivää juhlimme perjantaina. (Emphasizes whose birthday)
• Juhlimme perjantaina syntymäpäivää ystäväni. (Less usual, but possible)

Why are there no articles like “the” or “a” in this Finnish sentence?

Finnish doesn’t have definite or indefinite articles. Context and case marking do all the work. You simply say ystäväni for “my friend,” not the friend or a friend.