Ohne den Dosenöffner kann ich die Dose nicht öffnen.

Because ohne always takes the accusative case in German.

• der Dosenöffner = nominative
• den Dosenöffner = accusative

So after ohne, you need den:

• ohne den Dosenöffner

This is similar to learning that some English expressions always require a certain structure, except in German it affects the article form.

Because Dose is a feminine noun: die Dose.

In this sentence, die Dose is the direct object of öffnen, so it is in the accusative case. But for many feminine nouns, the article stays die in both nominative and accusative:

• nominative: die Dose
• accusative: die Dose

So even though the case changes, the form does not change here.

Because the sentence begins with Ohne den Dosenöffner, which counts as the first element in the sentence. In a German main clause, the finite verb must come in second position.

So the structure is:

• Ohne den Dosenöffner = position 1
• kann = position 2
• ich = then the subject comes after the verb

That is why you get:

• Ohne den Dosenöffner kann ich die Dose nicht öffnen.

If you start with the subject instead, you can say:

• Ich kann die Dose ohne den Dosenöffner nicht öffnen.

Both are correct.

Because kann is a modal verb. In German, when a modal verb is used, the second verb usually goes to the end in the infinitive form.

So here:

• kann = finite modal verb
• öffnen = infinitive at the end

This pattern is very common:

• Ich kann kommen.
• Sie will lernen.
• Wir müssen gehen.

So kann ich die Dose nicht öffnen follows a standard modal-verb pattern.

Because nicht usually comes before what it negates, and here it is negating the action öffnen.

So:

• die Dose nicht öffnen = not open the can

With infinitive verbs at the end, nicht often comes right before that final verb.

Compare:

• Ich kann die Dose nicht öffnen. = I cannot open the can.
• Ich öffne die Dose nicht. = I am not opening the can / I do not open the can.

In both cases, nicht is closely connected to the verb phrase.

It is a compound noun, which is very common in German.

• Dose = can / tin
• Öffner = opener
• Dosenöffner = can opener

The -n- in the middle comes from the plural form Dosen, which is often used as a linking form in compounds.

So literally, it is something like:

• can-opener

German often builds words this way instead of using separate words.

Because they are related words:

• öffnen = to open
• der Öffner = opener
• der Dosenöffner = can opener

German often forms nouns from verbs. So once you know öffnen, it becomes easier to understand words like:

• Türöffner = door opener
• Flaschenöffner = bottle opener

This is useful vocabulary-building: one verb can help you recognize many compound nouns.

The ö does not sound like ordinary English o.

A rough guide:

• ö is similar to the vowel in French peur or deux, if you know French.
• For English speakers, one trick is:
  1. Say ay as in say
  2. Keep your tongue in that position
  3. Round your lips as if saying o

That gets you close to ö.

Very roughly:

• öffnen sounds a bit like UF-nen, but with a rounded vowel that English does not really have
• Dosenöffner has ö in the second part as well

Also note:

• ff makes the preceding vowel short in öffnen
• Stress is usually on the first part of these words:
  • DO-sen-öff-ner
  • ÖFF-nen

Yes, absolutely. That is also correct.

Both of these are natural:

• Ohne den Dosenöffner kann ich die Dose nicht öffnen.
• Ich kann die Dose ohne den Dosenöffner nicht öffnen.

The difference is mainly focus:

• Starting with Ohne den Dosenöffner emphasizes the condition: without the can opener
• Starting with Ich is more neutral

German word order is flexible, but the finite verb still has to stay in second position in a main clause.

Because German können often covers both ability and possibility, much like English can, but usage does not always match perfectly in every context.

In this sentence, kann ich ... nicht öffnen means:

• I am not able to open it
• or practically, I can’t open it

It is about ability or practical possibility.

German können is one of the most common modal verbs, so this sentence is also a good example of how Germans express what someone is able or unable to do.