Icelandic has two possessive pronouns, minn (my) and þinn (your).
They inflect (change) depending on what it is you possess, and the possession can sometimes have the definite article (the word the in English), depending on the kind of thing you possess and how formal or informal you want to sound.
That sounds complicated. Let’s make it a little easier!
As a side-note: there are other ways to indicate possession in Icelandic, notably with:
The words minn and þinn inflect, depending on whether the thing you own is (grammatically) masculine, feminine, or neuter. It doesn’t matter if the owner is a man, woman, or anything in between.
Notice that minn and þinn are always identical to each other, except for the first letter, m or þ.
Notice the word order, too. The pronoun comes after the possession: it’s not my son, it’s son my; it’s not my house, it’s the house my. I’ll go into why it’s the house below.
Like most pronouns, minn and þinn also inflect with case (nominative, accusative, dative, and genitive). Check out [Basics of Cases if you’re unsure about how cases work in general.
To learn how to decline nouns I recommend Brian Casper’s YouTube channel, Icelandic For Foreigners, starting with this video.
Minn and þinn also inflect with number, of course.
Notice that the dative and genitive is the same across all genders in the plural. Makes it easier to learn! I've gone ahead and boxed those together to make that easier to see.
You often (but not always) use the definite article (the word the in English) with the thing you possess, and it depends on what type of possession you’re talking about. There are four types of possession.
Possession of body parts is a bit different; ordinarily, you probably shouldn’t use minn or þinn with those. You can check out Possession and Body Parts for an in-depth dive into that.
Man, four different types of words being treated differently sounds really complicated. You can make it simpler by just mastering the colloquial style. That’s what you would use in regular day-to-day talk with friends and family. I wouldn’t use it if you’re writing an academic paper or something fancy like that, though.
The language is constantly evolving. There is a trend to generalise the rules for concrete nouns and use the definite article with abstract nouns and body parts (not relations, though; that would still sound crazy).
Conversely, if you want to be extra formal, you can treat ALL words like abstract nouns and skip the definite article. Don’t do this in casual conversation, though, or you’ll sound stuffy.
Minn and þinn inflect, like most pronouns. If you’re a beginner, focus on just the gender in the nominative singular. Then later add in case and number.
The definite article plays a role in possession. If you’re a beginner, or if you’re just aiming for spoken fluency, just master the colloquial style.
If you have high ambitions, such as for academia or politics, I salute you! Get good at everything.