Learn Hardcore Icelandic: Gefðu mér vatn.

In Icelandic imperatives the subject pronoun þú is omitted because the verb ending -ðu (for second person singular) already indicates the subject. So gefðu on its own means ‘you give’.

How is the imperative gefðu formed from the infinitive að gefa?

To make the 2nd person singular imperative of gefa, drop the infinitive -a to get the stem gef-, then add -ðu. Hence gef- + ðu = gefðu.

Why is mér used instead of mig in this sentence?

The verb gefa (‘to give’) is ditransitive: it takes a dative object for the recipient and an accusative object for the thing given. mér is the dative form of ég, so it marks the person receiving the water (‘to me’).

Why is there no preposition (like “til”) before mér to indicate “to me”?

In Icelandic, verbs like gefa govern the dative case directly for the indirect object, so you don’t need a preposition. The dative form mér inherently means “to me.”

What case is vatn in, and why does it look like the nominative?

vatn here is the direct object in the accusative, but since vatn is a neuter noun, its accusative singular form is identical to its nominative singular (vatn). That’s why the form doesn’t change.

Why isn’t there a definite article before vatn (i.e., why not vatnið)?

Because you’re asking for some water rather than a specific body of water. The indefinite form has no article. If you wanted the specific water, you’d say gefðu mér vatnið.

Can you swap the order of mér and vatn in the sentence?

Grammatically you could say Gefðu vatn mér, but it sounds quite unnatural. The usual order in a ditransitive construction is verb + dative (recipient) + accusative (thing given).

How would you make this request more polite or address multiple people?

To be more polite you might use the conditional and add vinsamlegast (‘please’), for example:
“Gætirðu gefið mér vatn, vinsamlegast?” (‘Could you give me water, please?’).
To address more than one person (or as a polite plural), use the plural imperative gefið:
“Gefið mér vatn, vinsamlegast.”