Questions & Answers about Isolla koiralla on tapana raapia ovea.
Why is the subject 'the big dog' in the adessive case (isolla koiralla) instead of the nominative (iso koira)?
This is the core of the on tapana (has a habit of) construction. Just like the standard Finnish 'to have' construction (e.g., minulla on), the entity that possesses the habit must be in the adessive case. Notice that the adjective iso must also agree with the noun's case, becoming isolla.
Why does the word tapa (habit) have the -na ending here?
The -na suffix is the essive case ending, which often translates to 'as a' or 'in the role of'. The phrase on tapana is a fixed grammatical expression. Literally, this construction translates to 'On the big dog is as a habit to scratch the door'.
Why is the object of the scratching (ovea) in the partitive case?
The verb raapia (to scratch) is an irresultative verb, meaning it expresses an ongoing action without a definite, completed endpoint. Continuous actions like this require their objects to be in the partitive case.
Could I use the 3rd infinitive form (raapimaan) instead of the 1st infinitive (raapia)?
No, the on tapana structure strictly requires the 1st infinitive, which is the standard dictionary form of the verb. You would use the 3rd infinitive (-maan / -mään) with verbs expressing the start of an action, such as koira rupesi raapimaan ovea (the dog started to scratch the door).