Tjörnin er ekki djúp, en hafið er mjög djúpt.

The pond is not deep, but the sea is very deep.

Breakdown of Tjörnin er ekki djúp, en hafið er mjög djúpt.

• vera: to be
• ekki: not
• mjög: very
• en: but
• hafið: the sea
• tjörnin: the pond
• djúpur: deep

Questions & Answers about Tjörnin er ekki djúp, en hafið er mjög djúpt.

Why is it djúp in the first part and djúpt in the second part?

Both words come from the same adjective, djúpur (deep), but Icelandic adjectives change their endings to agree with the noun’s gender, number, and case.

• Tjörnin is feminine singular nominative → the adjective takes the feminine nominative singular form: djúp.
• hafið is neuter singular nominative → the adjective takes the neuter nominative singular form: djúpt.

So:

• Tjörnin er djúp = The pond is deep. (feminine)
• Hafið er djúpt = The ocean is deep. (neuter)

What is the difference between Tjörnin and tjörn?

Tjörn is the basic noun meaning pond.
Tjörnin is tjörn + the, i.e. the pond.

Icelandic usually adds the definite article as a suffix:

• tjörn = a pond
• tjörn + in → Tjörnin = the pond

Because it starts with tj, the t in the ending appears as -in, not -tin. The -in here is the feminine singular definite ending in the nominative case.

What does hafið mean, and how is it formed?

The basic word is haf, which means sea or ocean.
To say the sea / the ocean, Icelandic adds a definite ending:

• haf = sea / ocean
• haf + ið → hafið = the sea / the ocean

Here -ið is the neuter singular definite ending in the nominative case. So hafið literally means the sea / the ocean as the subject of the sentence.

Why is the negation ekki placed after er, not before it?

In Icelandic, the normal word order is:

Subject – Verb – (Negation/Adverbs) – Rest of the sentence

So you get:

• Tjörnin er ekki djúp.
  
  • Tjörnin (subject)
  • er (verb is)
  • ekki (negation not)
  • djúp (adjective deep)

Putting ekki before er (*Tjörnin ekki er djúp) would be ungrammatical in standard Icelandic. The position of ekki after the finite verb is very regular in main clauses.

What exactly does en mean here, and how is it different from og?

In this sentence, en means but:

• Tjörnin er ekki djúp, en hafið er mjög djúpt.
  → The pond is not deep, *but the ocean is very deep.*

og means and, used when you just add information without contrast:

• Tjörnin er djúp og falleg.
  → The pond is deep *and beautiful.*

So:

• en = but, introduces a contrast.
• og = and, simply adds something.

Why is it hafið er mjög djúpt and not mjög er djúpt or er djúpt mjög?

The typical place for adverbs like mjög (very) is right before the adjective they modify.

The structure here is:

• hafið (subject)
• er (verb)
• mjög (adverb very)
• djúpt (adjective deep)

So:

• hafið er mjög djúpt = the sea is very deep (correct, natural word order)
• *hafið er djúpt mjög sounds wrong or at best very unnatural.
• *hafið mjög er djúpt or *mjög er hafið djúpt are ungrammatical.

In simple sentences, keep mjög directly before the adjective: mjög djúpur / djúp / djúpt.

Why does Icelandic attach the equivalent of “the” to the noun (like -in, -ið) instead of having a separate word?

That is simply how definiteness is expressed in the standard modern language. Icelandic can use separate definite articles, but they are:

• Rare and mostly archaic or poetic (hinn, hin, hið).
• Not used in everyday speech in the way English uses the.

So instead of:

• the pond → the tjörn (not used)
  Icelandic does:

• the pond → Tjörnin (noun + definite ending)
• the sea → hafið

This pattern is shared with other Scandinavian languages (like Danish, Swedish, Norwegian), where definiteness is mostly suffixal.

Why are Tjörnin and hafið in the nominative case here?

They are both subjects of their clauses:

• Tjörnin er ekki djúp.
• hafið er mjög djúpt.

In Icelandic, the subject of a normal “to be” sentence (copula + description) is usually in the nominative case. The adjectives (djúp, djúpt) also appear in the nominative, agreeing with these nominative subjects.

You would see other cases (accusative, dative, genitive) with different verbs or prepositions, but with simple “X is Y” sentences, nominative is the default.

Could you give the basic forms (dictionary forms) of the main Icelandic words in the sentence?

Yes, here are the dictionary forms (usually nominative singular indefinite):

• Tjörnin → tjörn (pond, feminine)
• er → vera (to be, verb; er is present 3rd person singular)
• ekki → ekki (not, adverb; same as dictionary form)
• djúp / djúpt → djúpur (deep, adjective, masculine nominative singular is the dictionary form)
• en → en (but, conjunction; same form)
• hafið → haf (sea / ocean, neuter)
• mjög → mjög (very, adverb; same as dictionary form)

Are hafið and sjórinn the same thing?

Both refer to the sea, but there is a nuance:

• haf / hafið often suggests the open sea / the ocean, something vast and sometimes a bit poetic or literary.
• sjór / sjórinn is the sea as water, especially near the coast, what you swim in, sail on, etc.

In many contexts, both could be translated as the sea, but hafið typically fits better with the idea of something very vast and deep, which matches mjög djúpt well here.

If I change the nouns, do the adjective endings change in the same way?

Yes. The adjective must always agree with the noun in gender, number, and case. Examples in the same structure:

• Stelpan er ekki há, en maðurinn er mjög hár.

  • stelpan (fem.) → há (feminine form of tall)
  • maðurinn (masc.) → hár (masculine form)

• Húsið er ekki stórt, en bílarnir eru mjög stórir.

  • húsið (neuter sing.) → stórt (neuter singular)
  • bílarnir (masc. plural) → stórir (masculine plural)

In your sentence:

• Tjörnin (feminine sing.) → djúp
• hafið (neuter sing.) → djúpt