Learn Finnish: He ovat tukeneet ilmaista kampanjaa. - They have supported the free campaign.

Tukea (to support) is a type 1 verb. To form the plural past participle, you take the strong stem tuke- and add the plural marker -neet. Remember that active past participles for type 1 verbs always use the strong grade, keeping the k, even though it disappears in forms like tuen (I support).

Why are both ilmaista and kampanjaa in the partitive case?

The verb tukea is a partitive verb, meaning its object must always take the partitive case. Because the noun kampanjaa is in the partitive, the adjective describing it, ilmainen (free), must also be in the partitive to match.

How does the dictionary form ilmainen become ilmaista?

For words ending in -nen, the stem changes by replacing -nen with -s- before adding case endings. To form the partitive, we use this -s- stem (ilmais-) and add the partitive ending -ta, giving us ilmaista.

Why use ovat tukeneet instead of the basic past tense tukivat?

Ovat tukeneet is the perfect tense (they have supported), formed with the auxiliary verb olla (to be) and the past participle. You use this instead of the simple past tukivat (they supported) when the action connects to the present or its exact time isn't the main focus, just like in English.