Learn Hardcore Polish: W kuchni używam ostrego noża tylko do krojenia chleba. - In the kitchen I use a sharp knife only for cutting bread.

You might see w with the accusative in other contexts, where it means “into” rather than “in” (e.g. w wodę “into the water”), but for a simple location like here, you use w + locative → w kuchni.

What form is używam, and why not something like użyję?

Używam is:

1st person singular (I)
present tense
imperfective aspect
from the verb używać – “to use (habitually / generally)”

So używam means “I use / I am using” in a general or habitual sense.

There is also a perfective verb użyć:

użyję = “I will use (once, in a specific instance)”

In this sentence, you are describing a habit / general rule (“In the kitchen I (always) use a sharp knife only for cutting bread”), so the imperfective używam is correct.

Why is it ostrego noża and not the dictionary form ostry nóż?

Ostry nóż is the nominative:

ostry – “sharp” (masculine nominative singular)
nóż – “knife” (masculine nominative singular)

But after the verb używać, Polish normally uses the genitive case for the thing that is used.

Genitive singular of nóż: noża
Genitive singular of ostry: ostrego

So:

nominative: ostry nóż – “a sharp knife” (as the subject, or dictionary phrase)
genitive: ostrego noża – “of a sharp knife” (used after używać)

Because the sentence has używam (czego?) ostrego noża – “I use (what?) a sharp knife” – you must use ostrego noża.

Does używać always take the genitive, like in używam ostrego noża?

Yes, używać normally takes a genitive object:

używam noża – I use a knife
używasz komputera – you use a computer
używamy telefonu – we use the phone

You cannot say używam ostrym nożem (instrumental) with this verb.
If you specifically want the instrumental, you use a different verb, for example:

posługuję się ostrym nożem – I use / I make use of a sharp knife (here ostrym nożem is instrumental)

What exactly does tylko do here, and where can it go in the sentence?

Tylko means “only / just”.
In Używam ostrego noża tylko do krojenia chleba, it focuses on the purpose:

“I use a sharp knife only for cutting bread (and not for other things).”

In Polish, tylko is quite flexible in position, and where you put it changes what is being limited:

Tylko w kuchni używam ostrego noża do krojenia chleba.
→ Only in the kitchen do I use a sharp knife to cut bread.
Używam tylko ostrego noża do krojenia chleba.
→ I use only a sharp knife to cut bread (no other kind of knife or tool).
Używam ostrego noża tylko do krojenia chleba.
→ I use a sharp knife only for cutting bread.

So tylko comes directly before the word/phrase it “limits”.

Why is it do krojenia and not something like żeby kroić?

Both are possible, but they are different constructions:

do krojenia
- do
  - verbal noun (krojenie → krojenia, genitive)
- literally: “for the cutting (of) …”
- This is a very common and natural way to express purpose with tools and functions:
  - nożyczki do papieru – scissors for paper
  - maszyna do szycia – sewing machine
  - nóż do krojenia chleba – knife for cutting bread
żeby kroić
- żeby
  - infinitive (“in order to cut”)
- Focuses more on someone’s intention or goal.

Your sentence could be rephrased:

W kuchni używam ostrego noża, żeby kroić chleb.
→ perfectly correct, slightly more “action/intention”-focused.
W kuchni używam ostrego noża tylko do krojenia chleba.
→ sounds more like you’re describing the function/use of that knife.

What is krojenia exactly? Is it a verb form?

Krojenia is not a finite verb; it is a verbal noun (a noun formed from a verb).

Verb: kroić – “to cut, to slice”
Verbal noun (nominative): krojenie – “cutting” (as a noun, like English “cutting” or “the cutting”)
Genitive: krojenia

After do, we need the genitive, so:

do krojenia – “for cutting”

So grammatically, krojenia behaves like a noun, not a verb, even though it keeps its “verb-like” meaning.

Why is it chleba and not chleb?

Chleb is a masculine noun:

nominative: chleb
genitive: chleba

In the phrase do krojenia chleba, chleba is in the genitive because it depends on the verbal noun krojenie:

krojenie (czego?) chleba – “the cutting of bread”

And the preposition do also requires genitive (do czego? – “for / to what?”).

So everything lines up for genitive:

do
- krojenia (czego?) chleba

You will often see chleba in genitive in other common phrases too:

kawałek chleba – a piece of bread
jem dużo chleba – I eat a lot of bread

Could I just say do krojenia chleb instead of do krojenia chleba?

No. After krojenie (as a noun) and do, the word chleb must be in the genitive case, which is chleba.

Correct:

do krojenia chleba

Incorrect:

✗ do krojenia chleb

How flexible is the word order in this sentence? Can I move parts around?

Polish word order is relatively flexible, especially in spoken language, but small changes can shift the emphasis. All of these are grammatically correct, but have slightly different focus:

W kuchni używam ostrego noża tylko do krojenia chleba.
(neutral; only the purpose is limited)
Tylko w kuchni używam ostrego noża do krojenia chleba.
(I do this only in the kitchen)
Używam tylko ostrego noża do krojenia chleba (w kuchni).
(I use only a sharp knife; nothing else)
Ostrego noża używam w kuchni tylko do krojenia chleba.
(stronger emphasis on ostrego noża – “As for the sharp knife, in the kitchen I use it only for cutting bread”)

The original sentence has a neutral, natural word order for everyday speech.

Can I drop w kuchni and still have a correct sentence?

Yes. Without w kuchni, you get:

Używam ostrego noża tylko do krojenia chleba.
→ “I use a sharp knife only for cutting bread.”

It’s still perfectly grammatical; you simply lose the location information. The rest of the grammar (cases, forms of words) stays exactly the same.