Ennen joulua kauppa on ruuhkainen.

to be

Breakdown of Ennen joulua kauppa on ruuhkainen.

• kauppa: the store
• ennen: before
• ruuhkainen: crowded

Questions & Answers about Ennen joulua kauppa on ruuhkainen.

Why is joulu in the form joulua here?

Because ennen (before) is a preposition that always takes the partitive case in modern standard Finnish.

• joulu = the basic form (nominative)
• joulua = partitive singular

So the pattern is:

• ennen + partitive
  
  • ennen joulua = before Christmas
  • ennen kesää = before summer
  • ennen kokousta = before the meeting

You cannot say ennen joulu in standard Finnish, and ennen joulun is not normal either (you would rather say joulun alla = “just before Christmas / in the run-up to Christmas”).

So joulua is there because the preposition ennen requires the partitive case.

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What exactly does ennen joulua do in the sentence, and can it move to another position?

Ennen joulua is a time adverbial, telling when the shop is busy.

In Finnish, time expressions can move quite freely:

• Ennen joulua kauppa on ruuhkainen.
• Kauppa on ruuhkainen ennen joulua.

Both are grammatically correct and mean the same thing. The difference is in emphasis / information structure:

• Ennen joulua kauppa on ruuhkainen.
  → Emphasis on ; that time is being contrasted with other times.