Learn Hardcore Croatian: On je danas umorniji nego jučer. - He is more tired today than yesterday.

Je is the present tense of the verb biti (to be) and here it means “is”. So On je danas umorniji nego jučer literally corresponds to “He is today more tired than yesterday.”

In Croatian, short forms of biti (je, sam, si, smo, ste, su) behave like clitics: they very strongly prefer the second position in the sentence or clause. That is why you get:

On je danas umorniji nego jučer.
not
Je on danas umorniji nego jučer. (this would be wrong in a normal statement)

You can change other parts of the word order, but je will still try to stay in the second spot:

Danas je on umorniji nego jučer. – Danas is first, so je still comes second.
On danas je umorniji nego jučer. – sounds odd; we normally avoid pushing je out of second position like this.

Why is umorniji one word instead of saying više umoran for “more tired”?

Croatian usually forms the comparative of adjectives by changing the adjective itself, not by adding a separate word like more:

umoran (tired) → umorniji (more tired)
pametan (smart) → pametniji (smarter)
lijep (beautiful) → ljepši (more beautiful)

So umorniji is the standard comparative form of umoran and is the natural, default way to say “more tired.”

You can sometimes hear više umoran, but that is:

less standard / more colloquial, and
usually used for strong emphasis or in a special context.

For normal comparative meaning, umorniji is what you should use.

How is umorniji formed from umoran, and what are the feminine and plural forms?

The base adjective is umoran (tired, masculine singular). To make the comparative:

The stem umoran is shortened to umorn-.
The comparative ending -iji is added.

So:

umoran → umorn-
- -iji → umorniji

Agreement with gender and number works like with normal adjectives:

Masculine singular: On je danas umorniji nego jučer.
(He is more tired today than yesterday.)
Feminine singular: Ona je danas umornija nego jučer.
(She is more tired today than yesterday.)
Neuter singular: Dijete je danas umornije nego jučer.
(The child is more tired today than yesterday.)
Masculine plural: Oni su danas umorniji nego jučer.
(They [masc./mixed] are more tired today than yesterday.)
Feminine plural: One su danas umornije nego jučer.
(They [fem.] are more tired today than yesterday.)

The -iji / -ija / -ije pattern is very common for comparatives of adjectives ending in -an, -en, -ar, etc.

What is the difference between nego and od in comparisons? Could I say On je danas umorniji od jučer?

Both nego and od can appear in comparisons, but they are used in different typical ways.

Od is most common when you compare with a noun or pronoun in the genitive:
- Viši je od oca. – He is taller than (his) father.
- Umorniji sam od tebe. – I am more tired than you.
Nego is especially common:
- with pronouns in the same case:
  Više radiš ti nego ja. – You work more than I do.
- with whole clauses or adverbs, like jučer, danas, prije:
  On je danas umorniji nego jučer.

In your sentence, the natural choice is:

On je danas umorniji nego jučer.

If you say od jučer, it usually means “since yesterday / from yesterday”, not a direct comparison:

Umoran sam od jučer. – I’ve been tired since yesterday (the tiredness has lasted from yesterday).

So for “more tired today than yesterday”, use nego jučer, not od jučer.

Why isn’t there a second verb after nego jučer, like nego što je bio jučer?

Croatian often omits repeated words in the second part of a comparison if they are obvious from context. The full, explicit version would be:

On je danas umorniji nego što je bio jučer.
(He is more tired today than he was yesterday.)

But because je bio is already clear from the first part (On je danas umorniji…), speakers normally leave it out and simply say:

On je danas umorniji nego jučer.

This kind of omission is very common and completely natural. You only expand it (with nego što je bio jučer) if you want to be extra clear, formal, or stylistically explicit.

Can I drop On and just say Danas je umorniji nego jučer?

Yes. In Croatian, subject pronouns (on, ona, oni, etc.) are often omitted because the verb form usually makes the subject clear.

So these are both correct:

On je danas umorniji nego jučer. – stresses “he” a bit more.
Danas je umorniji nego jučer. – simply states that he is more tired today; who is understood from context.

You only need On if:

you want to contrast it (On je danas umorniji, a ona je odmorna.)
or there is any ambiguity about who you are talking about.

Can the word order change, for example On je umorniji danas nego jučer or Danas je on umorniji nego jučer?

Yes, Croatian allows quite flexible word order, but the clitic je wants to stay in second position.

Some natural variants:

On je danas umorniji nego jučer.
– Neutral, very common.
Danas je on umorniji nego jučer.
– Emphasis on danas (“today”), and a slight highlighting of on.
Danas je umorniji nego jučer.
– No explicit subject; neutral statement about “him”.
On je danas umorniji nego jučer. vs. On je umorniji danas nego jučer.
– On je umorniji danas nego jučer is possible, but moving danas after umorniji slightly emphasizes the contrast danas vs. jučer.

Positions that are wrong or very unnatural:

Je on danas umorniji nego jučer. – wrong in a neutral statement (clitic cannot start the sentence).
On danas je umorniji nego jučer. – feels wrong; je gets pushed out of its preferred second position.

So you can play with the order for emphasis, but keep je early, usually as the second element.

What part of speech are danas and jučer, and do they ever change form?

Danas (today) and jučer (yesterday) are adverbs of time.

They do not decline (they don’t change endings for case, gender, number).
They stay the same in all contexts:
- Vidimo se danas. – See you today.
- On je jučer bio kod kuće. – He was at home yesterday.
- Danas je umorniji nego jučer. – Today he is more tired than yesterday.

So unlike nouns (which change forms), danas and jučer are invariable.

Are there any simple pronunciation tips for jučer and umorniji for an English speaker?

Yes, a few:

jučer
- ju = like English “you”
- čer = roughly like “cher” in “cherish” (but with a clear ch sound, not soft “sh”)
- Put it together: you-cher (two syllables: ju-čer).
umorniji
- Syllables: u-mor-ni-ji (4 syllables)
- Every vowel is pronounced clearly:
  - u like “oo” in “foot” (short);
  - o like “o” in “or” (but shorter);
  - i like “ee” in “see”.
- The j in -ji is like English “y” in “yes”.

Croatian pronunciation is quite regular: each letter almost always has the same sound, and every written vowel is pronounced.

How would the sentence change for a female subject or for they?

You mainly need to change the form of umorniji to agree with the subject’s gender and number, and change the verb je if the subject is plural.

Female subject (she):
- Ona je danas umornija nego jučer.
  - umornija = feminine singular comparative.
They (masculine or mixed group):
- Oni su danas umorniji nego jučer.
  - su = are (3rd person plural of biti),
  - umorniji = masculine plural form (same as masculine singular in this case, but context tells you it’s plural).
They (all female):
- One su danas umornije nego jučer.
  - umornije = feminine plural comparative.

So the pattern is:

singular: je
- umorniji / umornija / umornije
plural: su
- umorniji / umornije (depending on gender)