Learn Hardcore Icelandic: Hann er þakklátur fyrir hjálpina.

Hann – personal pronoun, 3rd person singular masculine nominative = he. It is the subject.
er – present tense of vera (to be), 3rd person singular = is. It’s a linking (copula) verb.
þakklátur – adjective meaning grateful / thankful, masculine nominative singular, agreeing with Hann. It’s the complement of er.
fyrir – preposition meaning here for / because of. It governs the case of the following noun.
hjálpina – the noun hjálp (help), feminine accusative singular definite = the help. It is the object of the preposition fyrir.

So the structure is: Subject – verb – predicative adjective – preposition + object.

Why is it þakklátur and not some other form like þakklát or þakklátt?

Icelandic adjectives must agree with the noun (or pronoun) they describe in gender, number, and case.

Here:

Hann is masculine, singular, nominative.
The adjective þakklátur is therefore also masculine singular nominative.

Other basic nominative forms of this adjective are:

Masculine singular: þakklátur
Feminine singular: þakklát
Neuter singular: þakklátt
Masculine plural: þakklátir
Feminine plural: þakklátar
Neuter plural: þakklát

Examples:

Hann er þakklátur. – He is grateful.
Hún er þakklát. – She is grateful.
Barnið er þakklátt. – The child is grateful.
Þau eru þakklát. – They (mixed/neutral group) are grateful.

How would you say She is grateful for the help in Icelandic?

You only need to change the pronoun and the adjective’s gender:

Hún er þakklát fyrir hjálpina.

Changes:

Hann → Hún (he → she)
þakklátur → þakklát (masculine → feminine)

The rest (er fyrir hjálpina) stays the same.

Why is it hjálpina and not just hjálp? What’s the difference?

hjálp = help (no article, general or unspecified).
hjálpin / hjálpina = the help (definite, specific help).

In this sentence hjálpina is:

hjálp (help)
- -in- definite article (the)
- -a accusative singular ending for a feminine definite noun
  → hjálpina = the help (as a direct, specific thing).

Meaning-wise:

Hann er þakklátur fyrir hjálpina.
= He is grateful for the help (some particular help we both know about).
Hann er þakklátur fyrir hjálp.
= He is grateful for help (more general, not tied to a clearly identified act of help, or less specific in context).

English often omits the with abstract or mass nouns (for help), but Icelandic is much happier using the definite form once the help is clearly identifiable.

Why is hjálpina in the accusative case?

Because of the preposition fyrir.

When fyrir means for / in return for / because of, it takes the accusative case.
Therefore its object hjálp must be in accusative: hjálpina (fem. acc. sg. definite).

Declension of hjálp (singular, key forms):

Nominative: hjálp – help (subject)
Accusative: hjálp – help (object, indefinite)
Nominative definite: hjálpin – the help
Accusative definite: hjálpina – the help (object)

So fyrir + hjálpina is structurally the same kind of thing as English for the help, but here the case ending -a signals accusative definite.

How is fyrir used here, and what other meanings can it have?

In Hann er þakklátur fyrir hjálpina:

fyrir means for / because of / in return for:
- þakklátur fyrir eitthvað = grateful for something.

Common uses of fyrir include:

For / because of / in exchange for (takes accusative):
- Takk fyrir matinn. – Thanks for the food.
- Hann fékk pening fyrir vinnuna. – He got money for the work.
In front of / before (in space or time):
- fyrir framan húsið – in front of the house
- fyrir hádegi – before noon

Here the exact case can vary with movement vs. location, but at your level the key point is:

With þakklátur fyrir X, X is accusative.

Why is there no separate word for the in this sentence?

Icelandic usually puts the definite article at the end of the noun (as a suffix), not as a separate word like English the.

Examples:

maður – man
maðurinn – the man
bíll – car
bíllinn – the car
hjálp – help
hjálpin / hjálpina – the help

So in hjálpina:

hjálp = help
-in- = the (definite article)
-a = accusative ending

The meaning for the help is expressed by fyrir hjálpina, with the built into the noun.

Can the word order be changed, for example to Hann er fyrir hjálpina þakklátur?

The natural, neutral word order is:

Hann er þakklátur fyrir hjálpina.

You can move parts around for emphasis, but it starts to sound literary or marked. For example:

Hann er fyrir hjálpina þakklátur.
– Possible, but sounds more stylistic / poetic; it puts special emphasis on fyrir hjálpina.

For everyday speech and writing, keep:

Subject – er – adjective – fyrir + object
→ Hann er þakklátur fyrir hjálpina.

How do you pronounce Hann er þakklátur fyrir hjálpina?

Approximate guide for an English speaker:

Hann – like hahnn, with a short a (as in father) and a double n (a bit longer n).
er – like ehr, similar to air but shorter.
þakklátur – roughly thahk-low-tur:
- þ like th in thing (never like this).
- a short as in father.
- kk is a strong k sound with a slight aspiration.
- á is a long au sound, roughly like ow in cow.
- Stress on the first syllable: ÞAKK-lá-tur.
fyrir – roughly FIH-rir:
- First i like i in bit, but a bit longer.
- Rolled or tapped r.
hjálpina – roughly HYOWL-pi-na:
- hj is a soft sound (like the German ich sound before á), so something like hy- rather than plain h.
- á again like ow in cow.
- lp pronounced together, not with a clear break.
- Stress on the first syllable: HJÁLP-i-na.

Full (broad) IPA approximation: [hanː ɛr ˈθaʰkːlauːtʏr ˈfɪːrɪr ˈçaul̥pɪna].

How would you say He is not grateful for the help and He was grateful for the help?

He is not grateful for the help:
- Hann er ekki þakklátur fyrir hjálpina.
Notes:
- ekki (not) typically goes after the verb er.
He was grateful for the help:
- Hann var þakklátur fyrir hjálpina.
Notes:
- var is the past tense of er (from vera, to be).
- The adjective and the rest of the structure stay the same.

Are there synonyms for þakklátur? When would you use them?

Yes, the main close synonym is:

þakksamur – also grateful / thankful.

Rough guidelines:

þakklátur – very common, neutral, works in almost any context.
þakksamur – also common, sometimes feels a bit more formal, old-fashioned, or used in religious / solemn language, though you will meet it in everyday contexts too.

Examples:

Ég er mjög þakklátur fyrir hjálpina. – I am very grateful for the help.
Við erum þakksamir fyrir allt sem þú gerðir. – We are grateful for everything you did.

In most situations, you can use þakklátur and þakksamur interchangeably without causing misunderstanding.

Is there a noun related to þakklátur, like gratitude in English?

Yes:

þakklæti (neuter noun) = gratitude, thankfulness.

Examples:

Ég ber mikla þakklæti til þín.
– I feel great gratitude towards you / I am very grateful to you.
Til að sýna þakklæti gaf hann henni gjöf.
– To show his gratitude he gave her a gift.

So:

þakklátur – grateful (adjective, describing a person)
þakklæti – gratitude (noun, the feeling/quality)

Where would you put an adverb like very in this sentence?

You generally put adverbs like mjög (very) before the adjective:

Hann er mjög þakklátur fyrir hjálpina.
– He is very grateful for the help.

Other examples with the same pattern:

Hún er alveg þakklát. – She is completely grateful.
Við erum ótrúlega þakklát. – We are incredibly grateful.

So the usual slot is:

er + adverb + adjective
→ er mjög þakklátur.