Questions & Answers about Miksi kirjoitat tästä kommentista?
Why do we use the elative case ending -sta on kommentista instead of a separate word for "about"?
When verbs like kirjoittaa (to write), puhua (to speak), or ajatella (to think) express what the communication or thought is about, Finnish doesn't use a separate preposition. Instead, the subject matter is put directly into the elative case (-sta or -stä).
Why is the word for "this" written as tästä?
This is the elative form of the demonstrative pronoun tämä (this). In Finnish, modifiers must match the case of the noun they describe. Since the noun takes the elative form kommentista, the pronoun must also agree and become tästä.
Why does kommentti lose a "t" when it becomes kommentista?
This is a classic example of consonant gradation. The base noun kommentti contains the strong consonant cluster -ntt-. Because adding the ending -sta closes the final syllable, the strong -ntt- weakens to -nt-.
I see kirjoittaa also lost a "t" to become kirjoitat. Is that the exact same rule?
Yes! The infinitive kirjoittaa has a strong double -tt-. When you conjugate it for "you" by adding the personal ending -t, you close the syllable. This triggers the weak grade, reducing the double -tt- to a single -t-.