Kirjastonhoitaja tarkisti yhteystiedot, koska vanha puhelinnumero oli väärä.

The librarian checked the contact details because the old phone number was wrong.

Breakdown of Kirjastonhoitaja tarkisti yhteystiedot, koska vanha puhelinnumero oli väärä.

• olla: to be
• vanha: old
• koska: because
• tarkistaa: to check
• väärä: wrong
• kirjastonhoitaja: librarian
• yhteystieto: contact detail
• puhelinnumero: phone number

Questions & Answers about Kirjastonhoitaja tarkisti yhteystiedot, koska vanha puhelinnumero oli väärä.

Why is kirjastonhoitaja written as one word, and how is it formed?

Finnish often makes compound nouns where English would use multiple words.
kirjastonhoitaja = kirjasto (library) + -n (genitive marker) + hoitaja (caretaker/keeper) → literally the library’s keeper, i.e. librarian.
Writing it as one word signals it’s a single job title/role, not a noun phrase.

What does the -n in kirjaston- do?

The -n is the genitive case ending. In compounds it often marks a relationship like X’s Y or Y of X.
So kirjastonhoitaja is “library’s keeper/attendant” → librarian.

What tense is tarkisti, and what’s the dictionary form?

tarkisti is the past tense (imperfect) 3rd person singular: he/she checked.
Dictionary form: tarkistaa = to check / to verify.
The stem change is normal verb inflection: tarkista- + past marker -i → tarkisti.

Why is yhteystiedot plural, and what exactly does it mean?

Finnish usually treats “contact information/details” as plural: yhteystiedot literally means contact details (address, phone number, email, etc.).
Singular yhteystieto exists, but it tends to mean one specific piece of contact info.

What case is yhteystiedot in here, and why isn’t it partitive?

It’s the total object in the plural, and in Finnish the plural “accusative” looks the same as the plural nominative: yhteystiedot.
It’s not partitive (yhteystietoja) because the action is understood as complete: the librarian checked the contact details (as a whole set), not “some of them” or “was checking (ongoing)”.

Why is there a comma before koska?

In Finnish, a subordinate clause introduced by koska (because) is normally separated with a comma:

• Main clause: Kirjastonhoitaja tarkisti yhteystiedot,
• Because-clause: koska vanha puhelinnumero oli väärä.

Does koska affect word order in its clause?

Not in the same way as in German. The clause after koska typically keeps normal Finnish order (often S–V), though Finnish word order is flexible for emphasis.
Here it’s straightforward:

• vanha puhelinnumero (subject) + oli (verb) + väärä (predicate adjective)

Why is it vanha puhelinnumero (nominative) and not some other case?

Because it’s the subject of the oli (“was”) clause. Subjects are typically in the nominative:

• vanha puhelinnumero = “the old phone number”

Also, vanha agrees with puhelinnumero in case and number: both are singular nominative.

Why is it oli väärä and not oli väärin?

väärä is an adjective meaning wrong/incorrect, used to describe a noun:

• numero oli väärä = “the number was wrong”

väärin is an adverb meaning wrongly/incorrectly, used to describe an action:

• se oli kirjoitettu väärin = “it was written incorrectly”

Could I replace väärä with something else, like “incorrect”?

Often yes, depending on nuance:

• väärä = wrong (general, very common)
• virheellinen = erroneous/incorrect (more formal)
• viallinen = defective/faulty (more about something not functioning properly than being the wrong info)

For a phone number, väärä or virheellinen are the most natural choices.