Learn Finnish: Haluan syventyä tähän artikkeliin. - I want to delve into this article.

The verb syventyä (to delve into or immerse oneself) requires the illative case. Just like keskittyä (to focus on) from this lesson, verbs about directing your attention or committing to an action take the illative to show where your focus is going.

syventyä looks related to the word for deep (syvä). Is that right?

Yes! It is derived from the adjective syvä (deep). The suffix -ntyä turns it into an intransitive verb meaning to become deeper or to immerse oneself. So literally, you are deepening yourself into the article.

Why is the illative ending for artikkeli specifically -in?

The basic rule for forming the illative case is to double the final vowel and add n. Since artikkeli ends in a short i, you double it to get ii and add n, resulting in artikkeliin.

Do demonstrative pronouns like tämä always have to match the case of the noun?

Yes, demonstrative pronouns like tämä (this) must agree in case and number with the noun they modify. Since the verb rection forces the noun into the illative (artikkeliin), the pronoun must also take its illative form (tähän).