Learn Hardcore Croatian: Bez deke i jastuka ne mogu dobro spavati zimi. - Without the blanket and the pillow I cannot sleep well in winter.

So bez deke i jastuka literally means without (of) blanket and (of) pillow, which is how Croatian expresses “without a blanket and (a) pillow.”
Both nouns must be in the genitive because they are governed by bez.

Why are deka and jastuk in the singular and not plural, when in English I might say “without blankets and pillows”?

Croatian often uses the singular to talk about things in a general way, where English might use either a singular with an article or a plural:

bez deke i jastuka = without a blanket and (a) pillow / without blanket and pillow (general necessity)
bez deka i jastuka (both plural genitive) would mean “without any blankets and pillows” and sounds like you are stressing zero items.

So the singular here is natural and generic, not literally “only one blanket and one pillow.”

Where is the word “I” in this sentence? Why is ja missing?

Croatian is a “pro-drop” language: subject pronouns are usually omitted because the verb ending shows the person.

mogu = I can (1st person singular of moći, “to be able to”)
ne mogu = I can’t

So:

(Ja) ne mogu dobro spavati zimi.
The ja is optional and normally left out unless you want to emphasize I (e.g. “I can’t, but you can.”).

Why is it ne mogu spavati and not something like “ne mogu da spavam”?

In standard Croatian, after modal verbs like moći (can), morati (must), htjeti (want) you normally use the infinitive:

mogu spavati – I can sleep
ne mogu spavati – I can’t sleep

The structure ne mogu da spavam is more typical of Serbian and some dialects; Croatians understand it, but in standard Croatian ne mogu spavati is preferred and feels more natural.

Why is spavati in the infinitive, while mogu is conjugated?

In Croatian, as in English, a modal verb + main verb pattern is used:

English: I can sleep.
Croatian: (Ja) mogu spavati.

Here:

mogu – finite, present tense, 1st person singular (I can)
spavati – infinitive (to sleep)

So the modal verb moći carries the person/number, and the main verb spavati stays in the infinitive, without a separate word for “to”.

What is the function of dobro in ne mogu dobro spavati? Could it be dobar instead?

Dobro here is an adverb, modifying the verb spavati (“to sleep”):

dobro spavati – to sleep well

Dobar is an adjective (masculine form) and describes nouns, not verbs:

dobar čovjek – a good man
dobra deka – a good blanket (feminine)
dobro jelo – good food (neuter)

So you must use dobro with the verb:

✅ ne mogu dobro spavati – I can’t sleep well
❌ ne mogu dobar spavati – incorrect

Can I change the word order in ne mogu dobro spavati? For example, say ne mogu spavati dobro?

Yes, Croatian word order is quite flexible, especially with adverbs:

ne mogu dobro spavati
ne mogu spavati dobro

Both are grammatically correct and mean the same thing: I can’t sleep well.

Nuances:

ne mogu dobro spavati is the most neutral and common.
ne mogu spavati dobro might put a tiny bit more emphasis on how the sleeping is (the “well” part), but in everyday speech they’re practically interchangeable.

Why is it zimi and not u zimi or za zimu?

Zimi is the locative/dative singular form of zima (winter) and is very commonly used as a time expression meaning in (the) winter:

zimi – in winter / during winter

Using u zimi is grammatically possible but sounds unusual or overly literal; native speakers almost always just say zimi, or use:

tijekom zime – during winter
za vrijeme zime – during the time of winter

So:

ne mogu dobro spavati zimi = I can’t sleep well in winter.

Does zimi mean “in winter” or “in the winter”? There is no article—how do I know?

Croatian has no articles (“a”, “an”, “the”), so zimi can correspond to both:

in winter (general habit)
in the winter (this season, or in general)

The exact nuance comes from context, not from different words or forms. On its own, zimi just means in winter in a general sense.

What are the base forms of deke, jastuka, and zimi?

The dictionary (nominative singular) forms are:

deke → deka (blanket)
- deke here: genitive singular (after bez)
jastuka → jastuk (pillow)
- jastuka here: genitive singular (after bez)
zimi → zima (winter)
- zimi here: locative/dative singular, used as a time expression (in winter)

If bez already has a negative meaning (“without”), do I still need ne in ne mogu?

Yes, you still need ne to negate the verb:

mogu dobro spavati zimi – I can sleep well in winter.
ne mogu dobro spavati zimi – I cannot sleep well in winter.
bez deke i jastuka mogu dobro spavati zimi – Without a blanket and pillow, I can sleep well in winter. (opposite meaning!)
bez deke i jastuka ne mogu dobro spavati zimi – Without a blanket and pillow, I cannot sleep well in winter.

Bez only negates the presence of the objects (“without them”), not the verb itself. The verbal negation ne is still required.