Learn Hardcore Icelandic: Hann segir brandara og allir hlæja hátt. - He tells a joke and everyone laughs loudly.

In this sentence, brandari “a joke” is the direct object of segir “(he) says / tells”, so it must be in the accusative: Hann segir brandara = “He tells a joke.”

You would use brandari (nominative) only when it is the subject, e.g.

Brandari er fyndinn. – “The / a joke is funny.”

Why is it allir and not alla or öllum in allir hlæja hátt?

Allir is the nominative plural masculine form of allur (“all / everyone”). The subject of the clause must be in nominative, so:

allir = nominative plural (subject) → Allir hlæja hátt. – “Everybody laughs loudly.”
alla = accusative plural (object)
öllum = dative plural (indirect object / after many prepositions)

So you say Allir hlæja hátt, not Alla hlæja hátt, because “everybody” is doing the laughing.

Is hlæja here an infinitive or a present tense form? How does it work?

The verb hlæja has the same form for:

infinitive: að hlæja – “to laugh”
3rd person plural present: þeir hlæja – “they laugh”

In allir hlæja hátt, hlæja is 3rd person plural present, agreeing with allir (“everyone / all [they]”).

A simplified present-tense paradigm:

ég hlæ – I laugh
þú hlærð – you (sg.) laugh
hann / hún / það hlær – he / she / it laughs
við hlæjum – we laugh
þið hlæið – you (pl.) laugh
þeir / þær / þau hlæja – they laugh

So here allir = þeir grammatically, and that matches hlæja.

Why does hátt mean “loudly”? What form of the word is that?

Hátt comes from the adjective hár:

hár = “high, tall” and, for sounds, “loud”

The form hátt is neuter singular accusative, used adverbially. Icelandic very often uses the neuter singular of an adjective as an adverb, where English would use “-ly”:

hár → hátt = (speak) “loudly / loudly high”
hrár (“raw”) → hrátt (“raw / in a raw way”)
skýrt from skýr (“clear”) → “clearly”

So allir hlæja hátt literally is “everyone laughs loud (in a loud way)”, i.e. “everyone laughs loudly.”

Can I change the word order and say Hann segir brandara og hlæja allir hátt?

In normal Icelandic main clauses, the finite verb usually comes in second position (the “V2 rule”).

In the second clause, after og, the clause is:

subject: allir
finite verb: hlæja

So standard order is:

… og allir hlæja hátt.

If you say … og hlæja allir hátt, you put the verb first. That word order can appear in certain special contexts (questions, some emphatic structures, subordinate clauses), but as a simple continuation of this sentence it sounds strange / non‑standard. Stick to:

Hann segir brandara og allir hlæja hátt.

Why do we repeat the subject with allir? Why not just Hann segir brandara og hlæja hátt?

If you say:

Hann segir brandara og hlæja hátt,

Icelandic parses hann as the subject of both verbs:

“He tells a joke and (he) laughs loudly.”

But the intended meaning is that he tells the joke and everyone laughs. The subject changes from singular (hann) to plural (allir), so you must explicitly introduce the new subject:

Hann segir brandara og allir hlæja hátt. – “He tells a joke and everyone laughs loudly.”

Could I say Hann segir brandarann instead of Hann segir brandara? What is the difference?

Yes, grammatically you can, but the meaning changes:

Hann segir brandara. – “He tells a joke.” (indefinite, some joke)
Hann segir brandarann. – “He tells the joke.” (definite, a particular joke already known from context)

The difference is the definite article:

in Icelandic, it’s usually attached as a suffix:
- brandari – a joke
- brandarinn – the joke

In the accusative singular, that becomes:

brandara – (a) joke
brandarann – the joke

How is segja conjugated in the present tense? Why is it segir here?

Segja is the infinitive “to say / to tell.” The present tense:

ég segi – I say / tell
þú segir – you (sg.) say / tell
hann / hún / það segir – he / she / it says / tells
við segjum – we say / tell
þið segið – you (pl.) say / tell
þeir / þær / þau segja – they say / tell

In the sentence, the subject is hann, so you use hann segir – “he says / he tells.”

Does Hann segir brandara mean “He tells a joke” or “He is telling a joke right now”?

It can mean either, depending on context. Icelandic present tense covers both:

habitual / general:
- Hann segir oft brandara. – “He often tells jokes.”
right now:
- (Pointing at him) Hann segir brandara og allir hlæja hátt. – “He is telling a joke and everybody is laughing loudly.”

To be more clearly “right now”, speakers often rely on context or add time expressions like núna (“now”):

Hann er að segja brandara núna. (progressive-like “he is telling a joke now”) is also possible, using er að + infinitive.

What is the difference between hlæja and hlæja að e-m (“laugh at someone”)?

hlæja on its own = “to laugh” (no specified target):
- Allir hlæja hátt. – “Everyone laughs loudly.”
hlæja að e-m / e-u (+ dative) = “to laugh at someone / something,” often with a slightly mocking nuance:
- Allir hlæja að honum. – “Everyone laughs at him.”
- Hann segir brandara og allir hlæja að brandaranum. – “He tells a joke and everyone laughs at the joke.”

So if you only want to say they are laughing, use hlæja. If you want to say they are laughing at someone or something, use hlæja að + dative.

Can I drop hátt, or can I modify it, like mjög hátt? Where do these words go?

Yes:

Allir hlæja. – “Everyone laughs.” (no comment on loudness)
Allir hlæja hátt. – “Everyone laughs loudly.”

You can also use modifiers:

Allir hlæja mjög hátt. – “Everyone laughs very loudly.”
Allir hlæja rosalega hátt. – “Everyone laughs incredibly / really loudly.”

Typical order is:

subject – verb – adverb(s): Allir hlæja mjög hátt.

Putting hátt or mjög hátt after the verb is the most natural position in a simple sentence like this.

How do you pronounce hlæja and what sound is æ?

Very roughly (using English-like approximations):

æ is similar to the vowel in “eye” or “I”.
hlæja is about [ˈl̥ai.ja] in IPA.

Broken down:

hl-: the h makes the l voiceless; English speakers can think “h” + “l” together, but you just need some breath before the l.
-æ-: like “eye”.
-ja: like “ya” in “yard”.

So a rough approximation for learners: “HLAI-ya”, with a strong “eye” sound in the middle.