Learn Hardcore Croatian: Ne vidim ni njega ni nju u parku. - I see neither him nor her in the park.

You normally use ne with the verb and one or more negative words (like ni, nikad, nitko, nikoga, nigdje).
All these negatives work together as one logical negation, not as “two negatives make a positive” like in standard English.

In Ne vidim ni njega ni nju u parku:

ne vidim = I do not see
ni njega ni nju = neither him nor her

The whole thing means “I don’t see him or her in the park / I see neither him nor her in the park.”

You cannot just say Vidim ni njega ni nju (without ne) in standard Croatian; that would be wrong.
So:

✅ Ne vidim ni njega ni nju. = correct, normal Croatian
❌ Vidim ni njega ni nju. = incorrect

What case are njega and nju, and why?

Both njega and nju are in the accusative case, because they are the direct objects of the verb vidjeti (to see).

Roughly:

on = he (nominative, subject form)
njega = him (accusative/genitive, object form)
ona = she (nominative, subject form)
nju = her (accusative, object form)

So:

❌ Ne vidim on / ona u parku. — wrong, nominative can’t be used as object.
✅ Ne vidim njega ni nju u parku. — correct, accusative objects of vidim.

Note: for masculine animate pronouns like on, the accusative and genitive have the same form (njega). Here the function (object of vidim) tells you it’s accusative.

What is the difference between njega / nju and ga / je / ju? Why use njega / nju here?

Croatian has strong (stressed) and clitic (unstressed) forms of pronouns.

For he:

Strong (stressed): njega (accusative)
Clitic (unstressed): ga (accusative)

For she:

Strong (stressed): nju (accusative)
Clitic (unstressed): je / ju (accusative)

Typical uses:

Strong forms (njega, nju)
- used for emphasis, after prepositions, and in coordination like ni njega ni nju
- examples:
  - Vidim njega, a ne tebe. – I see him, not you.
  - Bez njega ne mogu. – I can’t do it without him.
  - Ne vidim ni njega ni nju. – I see neither him nor her.
Clitic forms (ga, je/ju)
- short, unstressed, usually right after the verb (or second position in the clause)
- examples:
  - Ne vidim ga. – I don’t see him.
  - Ne vidim je / ju. – I don’t see her.

In Ne vidim ni njega ni nju, coordination with ni … ni … strongly favors the full, stressed forms.
Forms like:

❌ Ne vidim ga ni je u parku. — feel unnatural / wrong in standard Croatian.
✅ Ne vidim ni njega ni nju u parku. — natural and standard.

Why is there no ja (“I”) in the sentence?

Croatian is a pro-drop language: subject pronouns are normally omitted when the verb ending already shows the person and number.

vidim = I see (1st person singular is clear from the ending -m)
So Ne vidim ni njega ni nju u parku already unambiguously means “I don’t see him/her in the park.”

You would use ja for emphasis or contrast:

Ja ne vidim ni njega ni nju u parku.
= I (as opposed to someone else) don’t see either of them in the park.

In neutral speech, you usually leave out ja here.

Can the word order be changed, and does it change the meaning?

Yes, Croatian word order is fairly flexible. These are all grammatical but differ in emphasis:

Ne vidim ni njega ni nju u parku.
– Neutral: focus is on whom you don’t see; u parku is just added location.
U parku ne vidim ni njega ni nju.
– Emphasizes the place: In the park I don’t see them (maybe I see them elsewhere).
Ni njega ni nju ne vidim u parku.
– Emphasizes the two people: It’s them in particular that I don’t see in the park.

The basic meaning (you don’t see either of them in the park) stays the same; word order mainly adjusts focus and nuance, not grammar.

What exactly does ni … ni … mean, and how is it different from i … i … or ili … ili …?

The three patterns:

ni … ni … = neither … nor …
- Usually appears with a negative verb (ne):
- Ne vidim ni njega ni nju u parku.
  = I don’t see him or her / I see neither him nor her in the park.
i … i … = both … and …
- Used with an affirmative verb:
- Vidim i njega i nju u parku.
  = I see both him and her in the park.
ili … ili … = either … or … (choice / alternative)
- Ili on ili ona je u parku.
  = Either he or she is in the park.
- With negation, you’d still normally use ni … ni … for neither/nor:
  - Ne vidim ni njega ni nju. (preferred)
  - Ne vidim njega ili nju. – possible but can sound less clear / more like a logical statement than natural speech.

So in your sentence, ni … ni … is the natural way to express neither him nor her under negation.

What case is parku, and why is it parku and not park or parka?

parku is in the locative singular of park.

With the preposition u:

u
- locative = in a place (static location)
- Ne vidim ga u parku. – I don’t see him in the park.
- Sjedi u parku. – He’s sitting in the park.
u
- accusative = into a place (movement towards)
- Idem u park. – I’m going into the park.
- Ulazim u park. – I’m entering the park.

So in u parku, we have:

u (in) + parku (locative) = in the park (no movement implied).

Forms you asked about:

park – nominative/accusative singular (used as subject or with motion towards: u park)
parka – genitive singular (e.g. iz parka – out of/from the park)
parku – locative singular (e.g. u parku – in the park)

Can I use only one ni, like Ne vidim njega ni nju u parku? Is that wrong?

You will hear both patterns:

Ne vidim ni njega ni nju u parku.
Ne vidim njega ni nju u parku.

Pattern 1 (ni before each item) is the clearest and most standard way to say neither him nor her. It nicely mirrors English neither A nor B.

Pattern 2 (only one ni) is also used in real speech and is generally acceptable, but:

It can sound less balanced stylistically.
The first object (njega) is just a plain accusative; the negation is highlighted more on the second (ni nju), even though logically the negation covers both.

For learners, the safest, most textbook-like form is:

Ne vidim ni njega ni nju u parku.

Does ni njega ni nju always refer to exactly two people, or can I list more?

You can use ni to list more than two items. For example:

Ne vidim ni njega, ni nju, ni Marka, ni Anu u parku.
= I don’t see him, her, Mark, or Ana in the park.

Stylistically, you can:

repeat ni before each item:
- ni njega, ni nju, ni Marka, ni Anu (very clear, emphatic)
or, sometimes, use ni before some of them only, but repeating ni is the cleanest pattern, especially for learners.

So ni njega ni nju in your original sentence is just a simple case of this pattern with two people.

Could I express a similar idea using a single word like “nobody” instead of listing njega and nju?

Yes, you can use a negative pronoun instead of listing specific people, but the nuance changes:

Ne vidim ni njega ni nju u parku.
– Refers to two specific people (him and her).
Ne vidim nikoga u parku.
– nikoga = no one / nobody (accusative)
– Means you don’t see anyone at all in the park.

So:

If you want to say I don’t see those two particular people, use ni njega ni nju.
If you want to say I don’t see any person, use nikoga.