Learn Icelandic: Kakan er á diskinum í eldhúsinu. - The cake is on the plate in the kitchen.

In Icelandic, prepositions like á (on) and í (in) control the grammatical case of the noun that follows them. When they describe a fixed location or a state of rest, like a cake just sitting there, they require the dative case.

How is the word diskinum (the plate) built?

Diskur is a masculine noun. First, we form the dative singular by dropping the -ur and adding -i, making diski. To say 'the plate', we add the masculine dative definite ending -num to that dative form, resulting in diskinum.

How is eldhúsinu (the kitchen) built?

Eldhús is a neuter noun. Its dative singular is formed by adding an -i to the end, making eldhúsi. To make it definite, we attach the neuter dative definite ending -nu, giving us eldhúsinu.

Why does the ending for 'the' look different for the plate (-num) and the kitchen (-nu)?

The definite endings change based on the grammatical gender of the noun. Because diskur is masculine, its dative definite ending is -num. Because eldhús is neuter, its dative definite ending is just -nu.