Á borðinu eru vínber og pera, en peran er ekki eins sæt og vínberin.

Because Icelandic often puts a location or time phrase first when that is the setting of the sentence. After that, the finite verb usually comes in second position. This is part of Icelandic V2 word order.

So:

• Á borðinu eru vínber og pera
• literally: On the table are grapes and a pear

English often uses there are, but Icelandic does not need a dummy word like there here.

A more neutral order is also possible:

• Vínber og pera eru á borðinu

Both are grammatical, but the original sentence highlights where the items are.

Because á can take different cases depending on meaning.

Here it means on the table in a stationary sense, so á takes the dative case:

• á borðinu = on the table

The base noun is:

• borð = table or a table

And borðinu is the definite dative singular form, meaning the table after the preposition.

A useful contrast:

• á borðinu = on the table with location
• á borðið = onto the table with movement

Because the verb vera = to be agrees with the subject in number.

• eru = are for a plural subject
• er = is for a singular subject

In the first clause, the subject is:

• vínber og pera = grapes and a pear

That is a compound subject, so it is treated as plural:

• eru

In the second clause, the subject is only:

• peran = the pear

So the verb is singular:

• er

This is the difference between indefinite and definite.

• pera = a pear
• peran = the pear

In Icelandic, the definite article is usually attached to the end of the noun instead of being a separate word.

So the sentence first introduces the item as new information:

• pera = a pear

Then it refers back to that same item:

• peran = the pear

This is very natural, just like English often goes from a pear to the pear.

Again, this is an indefinite/definite contrast:

• vínber = grapes or a grape / grapes depending on context
• vínberin = the grapes

A tricky point is that vínber has the same form in the indefinite singular and indefinite plural. So context tells you which meaning is intended.

In this sentence, the meaning is clearly grapes, and then later:

• vínberin = the grapes

The second form is definite because it refers back to the grapes already mentioned.

Because the first clause introduces the objects, and the second clause talks about those same specific objects again.

So Icelandic does what English does:

• first mention: vínber og pera = grapes and a pear
• later reference: peran and vínberin = the pear and the grapes

This is a very common pattern in Icelandic.

This is the Icelandic pattern for not as sweet as.

The structure is:

• ekki eins + adjective + og

So here:

• ekki eins sæt og vínberin
• not as sweet as the grapes

Compare:

• eins sæt og vínberin = as sweet as the grapes
• ekki eins sæt og vínberin = not as sweet as the grapes

So eins ... og works like English as ... as.

Because sæt is the correct predicate form here, and it agrees with peran.

In:

• peran er sæt

the adjective describes the pear, so it must match peran in gender and number. Pera is feminine singular, and the correct form here is sæt.

A useful contrast:

• peran er sæt = the pear is sweet
• sæta peran = the sweet pear

So sæta is a form you often see when the adjective comes directly before a definite noun, but after er, the form here is sæt.

It agrees with peran.

The second clause is about the pear:

• peran er ekki eins sæt og vínberin

That means:

• the pear is not as sweet as the grapes

So the adjective describes the pear, not the grapes. The grapes are only the thing being compared to.

The two instances of og do different jobs.

First:

• vínber og pera
• here og simply means and

Second:

• eins sæt og vínberin
• here og is part of the comparison pattern eins ... og, meaning as ... as

So even though the word is the same, its role is different in each place.