Learn Hardcore Icelandic: Lestin kemur á réttum tíma.

Icelandic doesn’t use a separate article like “the.” Instead, definiteness is shown by adding a suffix to the noun. The base word lest means “train,” and adding -in gives lestin, “the train.” In this sentence we’re referring to a specific train schedule, so we use the definite form.

Why is kemur in the present tense instead of a past or a dedicated future tense?

Icelandic, like English, often uses the simple present to describe scheduled events in the near future. So Lestin kemur… literally “The train comes…” is understood as “The train arrives…,” even if that arrival is yet to occur. There is no separate future-tense verb required.

What case is tíma in, and why?

Here tíma is in the dative singular. That’s because the preposition á, when used in many time expressions (including á réttum tíma for “on time”), governs the dative case.

Why is the adjective réttur inflected as réttum?

Adjectives in Icelandic agree with their noun in gender, number, and case. Tími is masculine singular in the dative, so the strong adjective réttur takes the dative singular masculine ending -um, giving réttum.

Why is the preposition á used here instead of í or um?

The fixed idiom for “on time” in Icelandic is á réttum tíma. While í means “in” and um can mean “around/about,” neither conveys the precise idea of punctuality. Only á with the dative produces the correct sense.

Can the word order be changed for emphasis?

Yes. Icelandic follows a V2 (verb-second) rule, so you can front the time phrase without altering the core meaning:
Á réttum tíma kemur lestin.
This places emphasis on when the train arrives.