Questions & Answers about Tämä on vain alku.
Since this lesson is about limits, how would I use the new postpositions to say "from the beginning"?
You would put alku into the elative case (alusta) and add asti or saakka. For example, alusta asti or alusta saakka means "right from the beginning".
Can I use "vasta" instead of "vain" in this sentence?
Yes, and it is a very common variation! While vain simply means "only", using vasta adds a strong sense of time, meaning "only just" or "not until now". Saying Tämä on vasta alku emphasizes how early in the process you are, translating roughly to "This is only just the beginning."
Why doesn't "alku" take the partitive case here, since a "beginning" feels like an abstract concept?
In Finnish, a basic "A is B" sentence with the verb olla (to be) uses the nominative case for the complement if it is a singular, countable noun. Even though it is an abstract idea, alku acts as a complete, countable unit here. You would generally only use the partitive in an "A is B" sentence if the noun were an uncountable mass noun (like water or music).