Learn Hardcore Icelandic: Þér megið sitja þar inni.

Þér is the old/formal way to address one person politely (like German Sie). It takes plural verb agreement. In modern Icelandic, this is rare; people normally use:

Singular informal: þú
Plural: þið

So everyday speech would more likely say: Þú mátt sitja þar inni (1 person) or Þið megið sitja þar inni (several people).

Is Þér singular or plural in this sentence?

Singular, but formal. It uses plural verb forms by convention: Þér megið… to one person. If you are talking to several people, use þið megið….

Isn’t þér the dative of þú? How can it be a subject here?

Yes, þér (lowercase) is the dative singular of þú (e.g., Ég hjálpa þér = I help you). But in this sentence, Þér is a special nominative form used for formal address. Context tells you which function is intended:

Object dative: Ég gef þér bók (I give you a book).
Formal subject: Þér megið… (You may…).

Why megið and not mátt?

Because the formal subject Þér requires the 2nd person plural verb form. Present tense of mega (may/be allowed):

ég má
þú mátt
hann/hún/það má
við megum
þið megið
þeir/þær/þau mega

So with Þér (formal singular), you use megið.

Is megið indicative or subjunctive here?

Indicative (stating permission). Note: the 2nd person plural form megið looks the same in the subjunctive, but here the meaning is straightforward permission. Subjunctive megi often appears in wishes: Megi þér farnast vel! (May you fare well!).

Why is sitja in the infinitive and not sitjið?

Modal verbs like mega take a bare infinitive without að:

Correct: Þér megið sitja…
Incorrect: Þér megið sitjið…
No að: not megið að sitja.

Does sitja mean “to be sitting” or “to sit down”?

sitja = to be in a sitting state (stative).
setjast = to sit down (motion into sitting). So “You may sit in there (take a seat)” could be more naturally: Þú mátt setjast þar inni.

What exactly does þar inni mean, and how is it different from just inni?

inni = inside/indoors (location), general.
þar inni = “in there,” a specific inside place already known or indicated, away from both speaker and listener. If you just say …sitja inni, it means “sit indoors/inside” without pointing to a particular room.

How do þar, þarna, and hér differ?

hér = here (near the speaker).
þarna = there (often visible or being pointed at).
þar = there (previously mentioned or non-deictic “that place”). So:
hér inni = in here,
þarna inni = in there (right there),
þar inni = in there (that place we’re talking about).

What’s the difference between inn, inni, and inn í?

inn (adverb of motion): in(wards). E.g., Farðu inn = Go in.
inni (adverb of location): inside. E.g., Ég er inni = I’m inside.
inn í (particle + preposition): into (a specific place). E.g., Farðu inn í herbergið = Go into the room. With a stative verb like sitja, you use inni: sitja þar inni.

Can I change the word order?

Yes, within limits:

Neutral statement: Þér megið sitja þar inni.
Question (inversion): Megið þér sitja þar inni?
Fronting the place for emphasis: Þar inni megið þér sitja.
Þér megið þar inni sitja is possible but sounds marked/stylized.

How do I negate this?

Place ekki after the finite verb:

Þér megið ekki sitja þar inni. Everyday alternatives:
Þú mátt ekki sitja þar inni.
Þið megið ekki sitja þar inni.

Is this sentence natural in modern Icelandic?

Grammatically yes, but it sounds very formal/old-fashioned. More natural today:

To one person: Þú mátt (setjast) þarna inni.
To several: Þið megið (setjast) þarna inni.
Polite/impersonal: Má (setjast) þarna inni? / Vinsamlegast setjist þarna inni (to a group).

Any pronunciation tips for tricky parts?

Þ (þ) = unvoiced “th” in “thin.”
ð = voiced “th” in “this” (word-final may be weak/devoiced).
é = like “ye” in “yes” (short): Þér ≈ “th-yer.”
In megið, the g before i is palatalized, sounding like a y: [ME-yith].
inni has a long/doubled n: INN-i. Stress is on the first syllable: ÞÉR megið SItja ÞAR INni.

If I want to ask “May I sit in there?”, how do I say it?

Má ég sitja þarna inni? (general)
More natural if you mean “take a seat”: Má ég setjast þarna inni?

What are the object/possessive forms if I do use the formal Þér style?

Very formal/old-fashioned:

Accusative/Dative: yður (e.g., Ég þakka yður = I thank you).
Genitive/Possessive: yðar (e.g., Yðar bíll = your car). These are rarely used today outside very ceremonial contexts.

Is Þér capitalized for politeness?

Not in modern usage. It’s capitalized here only because it starts the sentence. Older formal writing sometimes capitalized Þér/Yður/Yðar, but that’s considered old-fashioned now.