Learn Hardcore Croatian: Kad je lift pokvaren, penjem se pješice uz stepenice. - When the elevator is broken, I go up the stairs on foot.

Kad is a shorter, more colloquial form, very common in speech and also fine in writing.
Kada is slightly more formal or emphatic, often preferred in careful writing.

In this sentence, both are correct:

Kad je lift pokvaren, penjem se pješice uz stepenice.
Kada je lift pokvaren, penjem se pješice uz stepenice.

The meaning doesn’t change.

Why is there a comma after pokvaren?

Because kad je lift pokvaren is a subordinate clause (a time clause: when the elevator is out of order), and penjem se pješice uz stepenice is the main clause (I go up the stairs on foot).

In Croatian, when a subordinate clause comes before the main clause, you normally put a comma between them:

Kad je lift pokvaren, penjem se pješice uz stepenice.

If you reverse the order, the comma is often omitted:

Penjem se pješice uz stepenice kad je lift pokvaren. (comma usually not needed)

What tense and structure is je pokvaren?

Je is the present tense of biti (to be), and pokvaren is an adjective derived from the verb pokvariti (to break, to spoil, to go out of order).

So:

je = is
pokvaren = broken, out of order

Together, je pokvaren literally means is broken / is out of order. It describes a state in the present, not a completed action.

Why do we say pokvaren and not something like slomljen for “broken”?

Croatian uses different adjectives for different kinds of “broken”:

pokvaren – not working, out of order (typical for machines, devices, appliances, elevators, phones, etc.)
slomljen – physically broken into pieces or cracked (a slomljena čaša = a broken glass, slomljena noga = a broken leg)

An elevator that does not work is pokvaren, not usually slomljen.

Why is the verb penjem se reflexive? What does se do here?

The base verb is penjati se = to climb, to go up (literally to climb oneself). It’s a reflexive verb by nature, so it always appears with se when used in this sense.

penjem se = I climb / I go up
penješ se = you (sg.) climb
penje se = he/she/it climbs

You cannot say penjem alone here; it sounds incomplete or wrong. The reflexive pronoun se is just part of the verb’s normal form.

Why is penjem se in the present tense, not future or something else?

This is the present tense used in a general, habitual sense:

Kad je lift pokvaren, penjem se pješice uz stepenice.
= Whenever the elevator is out of order, I (normally) go up the stairs on foot.

You are not describing one specific occasion, but a general rule or habit. Croatian (like English) uses the present tense for that.

What is the difference between penjati se and popeti se?

Both are related to climbing / going up, but they differ in aspect:

penjati se – imperfective: focuses on the process, repeated or ongoing action (to be climbing / to climb in general).
- Kad je lift pokvaren, penjem se… (habit, repeated action)
popeti se – perfective: focuses on the completed action (to climb up, to get to the top / to finish climbing).
- Kad je lift bio pokvaren, popeo sam se pješice uz stepenice.
  (When the elevator was out of order, I climbed up the stairs on foot. – one completed event in the past)

What does pješice literally mean? Is it necessary here?

Pješice means on foot.

penjem se uz stepenice – I go up the stairs (already suggests walking)
penjem se pješice uz stepenice – I go up the stairs on foot (explicitly says you are doing it by walking)

So pješice is not strictly necessary for meaning, but it:

emphasizes the means of transport (walking, not e.g. escalator or something else),
sounds very natural in sentences contrasting different ways of moving.

You could drop it and still be correct, but the original version is very idiomatic.

What’s the difference between pješice and pješke?

They are near-synonyms:

pješice – neutral, standard, perfectly fine in both speech and writing.
pješke – very common in everyday speech; in some regions it’s more natural than pješice.

Both mean on foot. In this sentence you could use either:

penjem se pješice uz stepenice
penjem se pješke uz stepenice

Why is it uz stepenice and not another preposition? What does uz mean?

The preposition uz with the accusative case often means:

up (along), alongside, by, next to

Here, uz stepenice can be understood as up the stairs / along the stairs.

Some alternatives:

uz stepenice – up the stairs (along them)
po stepenicama – literally on the stairs, often used with moving up or down; can also be fine: penjem se po stepenicama
uz stube – using stube (another word for stairs)

In the given sentence, uz stepenice is completely natural and idiomatic.

Why is stepenice plural? Can I say stepenica in singular?

Stepenice (stairs) are normally referred to in the plural, because you think of them as a series of steps:

stepenica (singular) = one individual step
stepenice (plural) = a staircase / stairs

In this context, you want the whole staircase, so uz stepenice is correct.

Is the word lift always used, or is there another word in Croatian?

Croatian has two common words:

lift – widely used, especially in everyday speech; understood everywhere.
dizalo – also correct; somewhat more formal or regionally preferred, and often seen in official or technical contexts.

You can say:

Kad je lift pokvaren…
Kad je dizalo pokvareno…

Note the agreement:

lift is masculine: lift je pokvaren
dizalo is neuter: dizalo je pokvareno

Could I change the word order to Kad je pokvaren lift?

Yes, it is grammatically possible, but it changes the emphasis:

Kad je lift pokvaren… – neutral, default order (subject lift, then verb je, then predicate pokvaren).
Kad je pokvaren lift… – puts more stress on lift, as in when it’s the elevator that is broken (and not something else).

For a simple, neutral sentence explaining a habit, Kad je lift pokvaren is more typical.

Can I put the main clause first: Penjem se pješice uz stepenice kad je lift pokvaren?

Yes. Both orders are correct:

Kad je lift pokvaren, penjem se pješice uz stepenice.
Penjem se pješice uz stepenice kad je lift pokvaren.

When the kad-clause comes second, the comma is usually omitted in standard writing. The meaning (a general habit) stays the same.