Learn Hardcore Finnish: Laitoin pienen paketin ylimmälle hyllylle. - I placed a small package on the top shelf.

The infinitive is laittaa (“to put”). It belongs to a type I verb. In the present tense you say laitan (“I put”), and in the past tense you replace the final –aa with –oin, giving laitoin (“I put” in the perfective past).

Why is pienen paketin in the genitive/accusative singular, not the nominative or partitive?

Because laitoin expresses a completed action on a definite object, Finnish uses the accusative singular (which looks the same as the genitive).

Nominative would be pieni paketti (basic dictionary form).
Partitive (for incomplete or ongoing actions) would be pientä pakettia.
Here the whole package was placed, so it’s pienen paketin.

How do adjectives agree with nouns in case? For example, why does pieni become pienen here?

In Finnish an adjective takes the same case ending as its head noun. Since paketti is in accusative/genitive singular paketin, the adjective pieni also gets –n and becomes pienen. If you had the partitive plural paketteja, the adjective would be pieniä paketteja.

What case is ylimmälle hyllylle, and why do both words end in –lle?

–lle marks the allative case, which indicates movement onto a surface or to a location. Both the superlative form ylin (stem ylimmä-) and the noun hylly must take –lle, giving ylimmälle and hyllylle. Together they mean “to/on the topmost shelf.”

How do you form the superlative of the adjective ylä, and why is the stem ylimmä- in ylimmälle?

The base adjective ylä (“upper”) has an irregular superlative ylin (“topmost”). When you add case endings, the strong-grade stem becomes ylimä- (with consonant gradation doubling the m). Adding allative –lle yields ylimmälle.

What is the difference between hyllylle and hyllyyn?

They are two different locative cases:

hyllylle (allative) = “onto the shelf” (movement on top of a surface).
hyllyyn (illative) = “into the shelf” (movement into an enclosed space).
Since a shelf is treated as a flat surface, you use –lle.

Could I say ylähyllylle instead of ylimmälle hyllylle?

Yes. ylähylly means “upper shelf,” so ylähyllylle (“to the upper shelf”) is perfectly natural. ylimmälle hyllylle emphasizes “the very topmost shelf,” especially when there are several.

How do you express articles (“a”/“the”) in Finnish? I don’t see any here.

Finnish has no separate words for “a” or “the.” Definiteness is shown by context, word order and case endings. pienen paketin can mean either “a small package” or “the small package.” If you want “that small package,” you could say sen pienen paketin.

Can I use panin or pistin instead of laitoin?

Yes. panin (from panna) and pistin (from pistää) are common synonyms for “I put.” They carry similar meaning here. laitoin is neutral and widely used, but Panin pienen paketin ylimmälle hyllylle or Pistin pienen paketin ylimmälle hyllylle are both correct.