Learn Finnish: Ovatko nämä paksut vihkot sinun? - Are these thick notebooks yours?

In Finnish, the subject of a basic "A is B" sentence is usually in the nominative case. Because we are talking about specific, countable objects as the subject ("these thick notebooks" as opposed to an undefined amount of "some notebooks"), we use the nominative plural ending -t instead of the partitive plural.

Why does the sentence start with "Ovatko"?

To form a yes/no question, you take the verb, add the question particle -ko or -kö, and move it to the front. Since the subject is plural (nämä paksut vihkot), we use the "they" form of the verb olla (to be), which is ovat, plus the particle -ko to make Ovatko.

Does the adjective "paksu" always change to match the noun?

Yes! In Finnish, adjectives and pronouns must match the noun they describe in both number and case. Since vihko becomes the nominative plural vihkot, the pronoun tämä (this) and the adjective paksu (thick) must also take their plural forms nämä and paksut.

Why is it just "sinun" at the end instead of having a possessive suffix like "vihkosi"?

The word sinun is the genitive form of sinä (you). While it usually translates to "your" before a noun, it can also stand entirely on its own to mean "yours", just like in English. Because the notebooks are already mentioned as the subject, you don't need to repeat the noun or use a possessive suffix here.