Questions & Answers about Hän löysi hyönteisen tästä lasista olutta.
Why does olutta stay in the partitive case while lasista takes the elative (-sta) ending?
This is a standard rule for measure and container phrases. When a container noun (lasi) is followed by the substance it holds (olut), the substance modifier is locked into the partitive case (olutta). It stays in the partitive no matter how the container declines. Therefore, "from a glass of beer" is lasista olutta, not lasista oluesta.
The English translation says "in this glass", so why does the Finnish use the elative case (tästä lasista = from this glass)?
This is due to the rection (case requirement) of the verb löytää (to find). In Finnish, you don't find things in a place; you conceptually pull them out of obscurity, so you find them from a place. Because of this, löytää requires a "from" case—either the elative (-sta/-stä) or ablative (-lta/-ltä).
Why is the object hyönteisen in the genitive-like accusative case instead of the partitive?
Finding something is generally a completed action where the entire object is discovered, so löytää takes a total object. Because the subject found one whole, specific insect, hyönteinen takes the accusative -n ending. If he had found an uncountable mass (like "He found sand"), it would be in the partitive.
Does the demonstrative pronoun tästä agree with the whole phrase or just lasista?