Learn Hardcore Croatian: Na zidu iznad stola visi kalendar na kojem pišem važne datume. - On the wall above the table hangs a calendar on which I write important dates.

Stavljam kalendar na zid. = I’m putting the calendar onto the wall.
(zid is accusative here, same form as nominative for masculine inanimate singular)

So:

Na zidu visi kalendar → The calendar is hanging on the wall (already there).
Stavim kalendar na zid → I put the calendar on the wall (movement to a new place).

Why is it iznad stola and not something like iznad stol? What case is stola?

Stola is the genitive singular of stol (“table”).

Some prepositions in Croatian always require the genitive case. Iznad (“above”) is one of them:

iznad + genitive

Declension:

stol (N) → stola (G)

Other common prepositions that take the genitive:
ispod (below), između (between), kod (at someone’s place), blizu (near).

So:

iznad stola = above the table
You cannot say iznad stol; that would be ungrammatical.

Why does the sentence start with Na zidu iznad stola instead of just Kalendar visi na zidu iznad stola?

Both word orders are possible and correct:

Na zidu iznad stola visi kalendar.
Kalendar visi na zidu iznad stola.

Croatian word order is quite flexible. Starting with Na zidu iznad stola:

Puts the location in focus first (you’re setting the scene: “On the wall above the table…”).
Then you reveal what’s there: visi kalendar (“there hangs a calendar”).

Starting with Kalendar focuses more on the calendar itself.

This kind of “place-first” word order is very natural in Croatian, especially in descriptions, narratives, and when you’re answering a question like:

Gdje visi kalendar? – Where does the calendar hang?
→ Na zidu iznad stola visi kalendar.

Why do we use visi instead of just je? Could I say Na zidu iznad stola je kalendar?

You can say:

Na zidu iznad stola je kalendar.
= On the wall above the table there is a calendar.

But visi (from visiti = “to hang, be hanging”) adds more precise meaning:

visi kalendar → the calendar is physically hanging, not just “there”.

Croatian frequently uses specific posture/position verbs instead of just biti (“to be”):

visiti – to hang (be hanging)
stajati – to stand (be upright)
ležati – to lie (be lying)
sjediti – to sit (be sitting)

So:

Na zidu iznad stola visi kalendar.
→ We know it’s hanging.
Na zidu iznad stola je kalendar.
→ Neutral existence/location; correct but less vivid.

Why is kalendar in that bare form? Does it have a case, and what gender is it?

Kalendar here is:

Nominative singular (the “dictionary form”)
Masculine gender

It’s the subject of the sentence:

što visi? – kalendar → what is hanging? – the calendar.

Basic declension of kalendar (masculine, like stol with an extra syllable):

N sg: kalendar
G sg: kalendara
D sg: kalendaru
A sg: kalendar
L sg: kalendaru
I sg: kalendarom

In this sentence we need the subject, so we use the nominative → kalendar.

What exactly is na kojem doing here, and what is kojem the form of?

Na kojem introduces a relative clause that describes kalendar:

kalendar na kojem pišem važne datume
→ the calendar on which I write important dates

Koji is the basic relative pronoun (“which/that/who”). It agrees with the noun it refers to:

Refers to → kalendar (masculine, singular)
Function in its own clause: object of na in a location sense → locative case

So:

masculine singular, locative of koji → kojem (also possible: kojome)

Hence:

na kojem (kalendaru) = on which (calendar)

You can think of it as replacing kalendaru:

Na kalendaru pišem važne datume.
→ Na kojem pišem važne datume.

Why is it na kojem (locative) and not na koji (accusative)? In English I’d say “on which I write…”, which sounds more like a direct object.

In Croatian, the case of the pronoun is determined by:

The preposition used (here, na), and
The meaning: location vs. movement.

In this sentence, the idea is:

I write on the calendar (it’s already there; the surface is fixed).

For location with na, you use the locative:

na + locative → na kojem

If the meaning were more like “onto which I write” (emphasis on movement onto the surface), you might encounter na koji, but for a habitual, static idea (“I keep my dates on that calendar”) na kojem is the natural and standard choice.

So:

na kojem (kalendaru) → on which (calendar) – locative, location.
na koji (kalendar) → onto which (calendar) – accusative, movement (much less likely here).

Could I say kalendar na koji pišem važne datume or use gdje instead of na kojem?

All of these are possible, but they differ slightly in style and nuance.

kalendar na kojem pišem važne datume – as in the sentence
- Standard, clear, explicit about “on which”.
- Very natural.
kalendar na koji pišem važne datume
- Grammatically possible, but sounds more like “onto which I write…”.
- Implies movement toward the calendar, less like a stable writing surface.
- Less idiomatic for a neutral description.
kalendar gdje pišem važne datume
- Uses gdje (“where”) instead of a relative pronoun.
- More colloquial; often heard in speech.
- Grammatically fine, but na kojem is more precise and a bit more formal.

For clear, standard language, kalendar na kojem pišem važne datume is the best choice.

Why is it pišem and not a future or some other tense? It sounds like a habitual action.

Croatian uses the present tense very often for:

Habits / repeated actions
General truths
Usual behavior

So pišem here means:

I (regularly / generally) write important dates on that calendar.

This is parallel to English present simple:

“I write important dates on it.” / “I put my important dates on it.”

You could use other tenses/aspects for different meanings:

napisat ću važne datume na kalendar – “I will write the important dates on the calendar.” (single future action)
pisao sam važne datume na tom kalendaru – “I used to write / I was writing important dates on that calendar.”

But for a general, ongoing habit, present tense, imperfective (pišem) is exactly what you want.

What is the difference between pisati and napisati here?

Croatian has aspect: most verbs come in imperfective (ongoing, repeated) and perfective (completed, single whole action) pairs.

pisati – imperfective
- Focus on the process or habit: to be writing, to (generally) write.
napisati – perfective
- Focus on the completed result: to write something and finish it.

In the sentence:

na kojem pišem važne datume
- Emphasis: Whenever needed, I write dates there; it’s my habit.
- So the imperfective pisati is correct.

If you use napisati, you’d talk about a single finished action:

Na tom kalendaru sam napisao važne datume.
→ I (have) written the important dates on that calendar. (they’re already written, completed action)

Why is it važne datume and not važni datumi?

Važne datume is accusative plural (direct object of pišem):

Što pišem? – važne datume. (What do I write? – important dates.)

Noun datum (masculine inanimate):

N pl: datumi
A pl: datume

Adjective važan (important):

N pl (m.) → važni
A pl (m.) → važne

So the forms match:

Nominative (as subject): važni datumi – important dates (are something)
Accusative (as object): važne datume – (I write) important dates

Because dates are the thing being written, accusative plural is required → važne datume.

Why do važne and datume look different? How do they agree?

Adjectives in Croatian must agree with the noun in:

Gender
Number
Case

Here:

Noun: datume
- datum → masculine, plural, accusative
Adjective: važne
- masculine, plural, accusative (matching datume)

Pattern:

N sg: važan datum
A sg: vidim važan datum
N pl: važni datumi
A pl: pišem važne datume

So:

važne (A pl masc)
datume (A pl masc)

They’re different forms, but they are in full agreement.

Is there any difference between na kojem and na kojemu?

Both are correct forms of the same case (masculine singular locative of koji):

na kojem – shorter, more common in everyday speech and writing.
na kojemu – slightly more formal/old‑fashioned, but still correct.

You can freely use na kojem in modern standard Croatian:

kalendar na kojem pišem važne datume ✔
kalendar na kojemu pišem važne datume ✔ (a bit more formal/literary)

The meaning is the same: “on which”.