Learn Hardcore Icelandic: Hún lætur mig vita ef fundurinn byrjar fyrr. - She lets me know if the meeting starts earlier.

It’s the causative construction with láta: láta + accusative object + bare infinitive. Here, læta “to cause/make/let” takes mig (accusative of “I”) and the infinitive vita (to know).

Hún lætur mig vita = She causes that I know → She lets me know.
Other examples: Ég lét hann bíða (I made him wait), Láttu mig vita (Let me know).

Why is it “mig” (accusative) and not “mér” (dative)?

Because láta takes its “causee” in the accusative. So it’s láta einhvern (ACC) + infinitive. By contrast, verbs like segja “to tell” take a dative recipient:

Hún lætur mig vita (ACC)
Hún segir mér frá fundinum (DAT)

Why is there no “að” before “vita”?

With láta (and also with modals like mega, geta, vilja, þurfa, skulu, munu), the infinitive appears without að. Hence láta mig vita, not láta mig að vita.

Can the present tense “lætur” refer to the future?

Yes. Icelandic commonly uses the present for near-future or scheduled events. You can add munu for an explicit future: Hún mun láta mig vita ef…, but it’s not necessary here.

Why is it “ef” and not “hvort”?

ef = if/in the event that (a condition). That’s what we want: she’ll notify me if the condition happens.
hvort = whether (A-or-B question). Use it when reporting an indirect yes/no question: Hún lætur mig vita hvort fundurinn byrjar fyrr (eða ekki). English “Let me know if…” is ambiguous; Icelandic disambiguates with ef (conditional) vs hvort (whether).

Is the word order “ef fundurinn byrjar fyrr” typical in a subordinate clause?

Yes. After the complementizer ef, Icelandic often keeps V2-like order: subject then finite verb. So ef fundurinn byrjar fyrr is natural. You can also front the whole clause:

Ef fundurinn byrjar fyrr, lætur hún mig vita.

What’s going on with “fundurinn”? Why is “the” stuck on the noun?

Icelandic uses a suffixed definite article. fundur (a meeting) → fundurinn (the meeting). Masculine singular nominative definite adds -inn. So fundurinn byrjar = “the meeting starts.”

Could I say “Hún lætur vita mig”?

No. In this construction the object comes between láta and the infinitive: láta + object + infinitive. So it must be Hún lætur mig vita, not …vita mig.

What is the nuance of “byrjar fyrr”? Could I use “hefst” instead?

byrja is the everyday verb “to start/begin.”
hefjast is a bit more formal/literary and intransitive. Both are fine here: ef fundurinn byrjar fyrr / ef fundurinn hefst fyrr.

How does “fyrr” differ from “snemma,” “áður,” and “fyrr en”?

fyrr = earlier/sooner (comparative adverb), often with an implied comparison: Fundurinn byrjar fyrr (en vanalega).
snemma = early (absolute): Fundurinn byrjar snemma.
áður = earlier/before (adverb): Hún fór áður.
fyrr en = before (conjunction): Farðu ekki fyrr en fundurinn er búinn.

Do I need a comma before “ef”?

Not necessarily. Modern Icelandic punctuation often omits a comma before a short ef-clause. You may add one in longer sentences or by older style, but it’s optional here.

Could the verb be subjunctive, like “byrji,” after “ef”?

Use indicative (byrjar) for a real/likely condition. Use the subjunctive for more hypothetical or tentative conditions, often with a conditional in the main clause:

Real: Ef fundurinn byrjar fyrr, lætur hún mig vita.
Hypothetical: Ef fundurinn byrji fyrr, myndi hún láta mig vita.

How would I say this as a request/imperative: “Let me know if the meeting starts earlier”?

Informal singular: Láttu mig vita ef fundurinn byrjar fyrr.
Plural/formal: Látið mig vita ef fundurinn byrjar fyrr.

Are there other ways to express “let (someone) know”?

Yes:

láta einhvern vita (neutral/common): Láttu mig vita.
segja einhverjum frá (tell someone about): Segðu mér frá því ef fundurinn byrjar fyrr.
Reflexive idiom: láta vita af sér (make contact/announce oneself): Láttu vita af þér. (Keep in touch/Let us hear from you.)

Any quick pronunciation tips for tricky parts?

æ in lætur sounds like the “i” in English “ice.”
mig is often pronounced like “miy” in everyday speech.
Double rr in fyrr is a trilled/tapped r.
j in byrjar is like English “y” in “yes.”