Húsið er fullt af bókum.

to be

Breakdown of Húsið er fullt af bókum.

• húsið: the house
• bókin: the book
• fullur: full
• af: of

Questions & Answers about Húsið er fullt af bókum.

Why is the word húsið spelled with -ið at the end?

In Icelandic the definite article is a suffix. hús means “a house,” and when you make it definite (“the house”) you attach -ið because hús is a neuter noun. Hence húsið = “the house.”

Why is fullt used here and why does it end in -t?

fullur is an adjective meaning “full.” Adjectives in Icelandic agree in gender, number and case with the noun they describe. Since húsið is neuter singular in the nominative, fullur takes its neuter nominative ending -t, giving fullt.

What case is bókum, and why is that case used?

bókum is the dative plural form of bók (“book”). The preposition af (here meaning “of”) always governs the dative. Moreover, the fixed expression fullur af requires its complement to be in the dative. Hence bókum.

What does the preposition af mean here, and can we omit it?

Here af means “of” in the sense “full of.” You cannot omit it, because fullur by itself does not take a direct object. To express what something is full of, you always need af + dative.

Why can’t I say Húsið er fullt bóka without af?

Because fullur is not a transitive adjective—it doesn’t directly take a noun. You must introduce the thing you’re “full” of with af. Without af, the sentence is ungrammatical.

Can I change the word order and say Af bókum er húsið fullt?

Yes, it’s grammatically possible but very marked or poetic. The neutral, everyday word order is Húsið er fullt af bókum. Starting with Af bókum puts heavy emphasis on “books” and feels literary.

If there were only one book, how would I express “full of a book”?

Grammatically you could say
 Húsið er fullt af bók.
Here bók is the dative singular form (unchanged spelling). If you want to stress exactly one, you’d add a numeral:
 Húsið er fullt af einni bók.

How would I say “The cup is full of water” using a similar structure?

Pick your noun (e.g. bolli = “cup”) and put it definite + correct adjective form + af + dative of vatn (“water”):
 Bollinn er fullur af vatni.
Or with glas (neuter):
 Glasið er fullt af vatni.

Is there another way to say that the house “has a lot of books” without fullt af?

Yes. Icelandic often uses an existential construction or different adjectives:
• Í húsinu eru margar bækur. (“There are many books in the house.”)
• Húsið er bókafyllt. (A compound adjective: “book-filled,” more colloquial.)
Both avoid fullt af but convey a similar idea.