Learn Hardcore Icelandic: Bókin er á gólfinu við rúmið.

Bókin = the book
- bók = book
- -in = the (definite article for many feminine nouns)
er = is (3rd person singular of vera = to be)
á = on (also in/at in other contexts)
gólfinu = the floor (in the dative case)
- gólf = floor (neuter noun)
- -inu = the (neuter, dative, singular)
við = by / next to / at (here: “by the bed”)
rúmið = the bed (in the accusative case)
- rúm = bed (neuter noun)
- -ið = the (neuter, nominative/accusative singular)

So the whole sentence means: “The book is on the floor by the bed.”

Why is it Bókin and not just bók?

Because Icelandic usually marks “the” by adding an ending to the noun instead of using a separate word.

bók = a book (indefinite, nominative singular)
bókin = the book (definite, nominative singular)

Here, “the book” is the subject of the sentence, so it’s in the nominative case, and we want it to be definite, so we use bókin.

Why is it á gólfinu and not á gólfið?

Because the preposition á (“on”) changes case depending on meaning:

á + accusative = movement onto/into something
- Ég set bókina á gólfið. = I put the book onto the floor.
á + dative = static location on/in/at something
- Bókin er á gólfinu. = The book is (lying) on the floor.

In Bókin er á gólfinu, the book is just located there; it’s not moving there. So á takes dative, and the dative definite form of gólf is gólfinu.

Forms of gólf (floor), singular:

Nom/Acc: gólf
Dat: gólfi
Def. Nom/Acc: gólfið
Def. Dat: gólfinu

Why is it við rúmið and not við rúminu?

Because the preposition við always governs the accusative case in this meaning (“by / next to / at”).

við
- accusative: physical closeness, “by / next to / against”
rúm is a neuter noun:
- Nom/Acc singular: rúm
- Def. Nom/Acc singular: rúmið
- Dat singular: rúmi
- Def. Dat singular: rúminu

Since við requires the accusative, we must use rúmið, not rúminu.

rúminu would be dative and is used after prepositions that take dative (like hjá: hjá rúminu = “by/at the bed” with a slightly different nuance).

Why do the endings look different: bókin, gólfinu, rúmið? Aren’t they all “the + noun”?

They’re all “the + noun”, but the endings change with gender and case.

Base forms:

bók = book (feminine)
gólf = floor (neuter)
rúm = bed (neuter)

In the sentence:

Bókin
- Feminine, nominative, singular, definite
- bók
  - -in → bókin = the book (subject)
Gólfinu
- Neuter, dative, singular, definite
- á (static location) → dative
- gólf
  - -inu → gólfinu = the floor (on the floor)
Rúmið
- Neuter, accusative, singular, definite
- við → accusative
- rúm
  - -ið → rúmið = the bed (by the bed)

So:

Feminine nominative definite often ends in -in (bókin).
Neuter accusative/nominative definite often ends in -ið (rúmið).
Neuter dative definite often ends in -inu (gólfinu).

Could I just say Bókin er á gólfinu? What changes in meaning?

Yes, that’s a perfectly correct sentence.

Bókin er á gólfinu. = The book is on the floor.

By omitting við rúmið, you lose the extra information about which part of the floor we’re talking about. The original sentence:

Bókin er á gólfinu við rúmið.
= The book is on the floor *by the bed.*

So við rúmið is an optional extra detail specifying location more precisely.

What exactly does við mean here? I thought við also meant “with”.

Við is a very flexible preposition. Some common meanings:

Physical closeness / next to / by / against
- Bókin er á gólfinu við rúmið.
  = The book is on the floor by/next to the bed.
- Hann stendur við gluggann.
  = He is standing by the window.
Against (physically or metaphorically)
- Stólinn stendur við vegginn. = The chair is against the wall.
- Ég er á móti þessu, en hún er við það. (“she is for it / in favour”) – more advanced use.
With (a person, in company with) often með is used instead of við for “with”, but you see við in some fixed expressions.

In this sentence, við means “by / next to”, indicating position close to the bed. It often suggests being right beside or even touching the thing.

How would I say “I put the book on the floor by the bed” in Icelandic?

You need to switch to a verb of placing and adjust the cases for movement:

A natural sentence:

Ég set bókina á gólfið við rúmið.

Breakdown:

Ég = I
set = put/place (present tense)
bókina = the book (accusative singular definite of bók; it’s the direct object)
á gólfið = onto the floor
- now á expresses movement → accusative → gólfið
við rúmið = by the bed (unchanged; við always takes accusative)

Contrast:

Bókin er á gólfinu… (is lying there, static, dative)
Ég set bókina á gólfið… (I move it there, accusative)

How would I say “The books are on the floor by the bed”?

You mainly need the plural of “book”:

Bækurnar eru á gólfinu við rúmið.

Changes:

bók → plural nominative definite bækurnar (irregular plural)
- Singular: bókin er… = The book is…
- Plural: bækurnar eru… = The books are…

The rest stays the same:

á gólfinu = on the floor (one floor, dative singular)
við rúmið = by the bed (one bed, accusative singular)

Could I use a different verb than er here, like something that means “lying”?

Yes. Er is a neutral “is”, but Icelandic often uses more specific posture verbs:

liggur = lies, is lying (for something lying flat)
stendur = stands, is standing (upright)
situr = sits, is sitting (sitting position)

So you can say:

Bókin liggur á gólfinu við rúmið.
= The book is lying on the floor by the bed.

This sounds a bit more descriptive than Bókin er á gólfinu við rúmið, but the original with er is completely natural and common.

Can I change the word order to Á gólfinu við rúmið er bókin?

Yes, that word order is grammatical and natural, but it changes the focus slightly.

Bókin er á gólfinu við rúmið.
Neutral: subject first. Stating a fact about “the book”.
Á gólfinu við rúmið er bókin.
Fronts the location phrase, so it sounds like you’re emphasizing where the book is.
This fits well as an answer to “Where is the book?”:
- Hvar er bókin? – Where is the book?
- Á gólfinu við rúmið er bókin. – On the floor by the bed is the book.

Everyday speech would more commonly answer with:

Hún er á gólfinu við rúmið. (using the pronoun hún “she/it” for bókin)

How do you pronounce Bókin er á gólfinu við rúmið?

A careful IPA transcription (approximate):

Bókin ≈ [ˈpouːcɪn]
er ≈ [ɛr]
á ≈ [auː]
gólfinu ≈ [ˈkoulvɪnʏ]
við ≈ [vɪð]
rúmið ≈ [ˈruːmɪð]

Rough pronunciation tips for an English speaker:

Stress is on the first syllable of Bókin, gólfinu, and rúmið.
ó is like the “o” in English go (but purer, no diphthong glide).
á is a diphthong like English ow in now.
ð is a soft “th” sound as in this (or very weak, sometimes almost silent at the end).
u / ú / ʏ vowels don’t match English exactly; you’ll need to learn them by ear, but this is close enough to be understood.