Bez důkazu se nemůžu odvolat.

Because the preposition bez always takes the genitive case in Czech.

The base noun is důkaz (proof, evidence).
Its genitive singular form is důkazu.

So:

• důkaz = proof/evidence
• bez důkazu = without proof / without evidence

This is a very common pattern:

• bez cukru = without sugar
• bez problémů = without problems
• bez času = without time

So in this sentence, bez forces důkaz into the genitive.

Yes, singular is used here because it means without proof / without any evidence in a general sense.

Czech often uses the singular where English might also use an uncountable idea like proof or evidence.
So bez důkazu sounds natural.

You could use a plural form in a different context, for example:

• bez důkazů = without proofs / without pieces of evidence

But in ordinary legal or formal language, bez důkazu is the most natural way to express the idea.

Se is a reflexive particle that belongs to the verb odvolat se.

The verb is not just odvolat here. The expression is:

• odvolat se = to appeal

Without se, odvolat usually means something else, such as to recall, to call off, or to revoke, depending on context.

So in this sentence, se is essential.
You should learn odvolat se as a whole unit.

Not really in natural English terms. Even though se is historically reflexive, in many Czech verbs it is simply part of the verb and does not have a directly translatable meaning.

So it is best not to over-translate it. Just learn:

• odvolat se = to appeal

Similarly, Czech has many verbs where se is just part of the standard form:

• smát se = to laugh
• bát se = to fear / be afraid
• dívat se = to look, watch

Nemůžu is the 1st person singular present tense of moct/moci, so it means I can't.

Here are common forms:

• můžu / mohu = I can
• nemůžu / nemohu = I can't

Both nemůžu and nemohu are correct:

• nemůžu is more common in everyday speech
• nemohu sounds more formal or written

So Bez důkazu se nemůžu odvolat is perfectly natural spoken Czech.

They mean the same thing: I can't.

The difference is mostly style:

• nemůžu = common, conversational, natural in everyday speech
• nemohu = more formal, more typical in careful writing or official style

So depending on tone, you might hear either:

• Bez důkazu se nemůžu odvolat.
• Bez důkazu se nemohu odvolat.

Both are correct.

This is about Czech word order and clitics.

Se is a clitic, which means it tends to stand in the second position of the sentence or clause.

In this sentence, the first unit is:

• Bez důkazu

So the clitic se comes right after that:

• Bez důkazu se nemůžu odvolat.

This is very natural Czech word order.

You could also say:

• Nemůžu se bez důkazu odvolat.

That is also correct. But in the given sentence, the speaker is emphasizing without proof by putting it first.

That sounds much less natural.

The problem is the placement of se. Since se is a clitic, it normally wants to appear early, in the second position of the clause.

So Czech strongly prefers:

• Bez důkazu se nemůžu odvolat.

rather than:

• Bez důkazu nemůžu se odvolat.

In other words, se usually comes before the main stressed part of the verb phrase, not after nemůžu in this kind of sentence.

Odvolat se is the perfective form. Its imperfective partner is odvolávat se.

In many cases, after a modal verb like můžu, Czech chooses aspect based on meaning:

• odvolat se = to file/make an appeal as a complete act
• odvolávat se = to be appealing, to appeal repeatedly, or to focus on the ongoing process

Here, the speaker means a single concrete act: I can't appeal.
That is why the perfective odvolat se is natural.

Yes. It often means to appeal, especially in legal or official contexts, but it can also mean to refer to or invoke something, depending on the construction.

For example:

• odvolat se proti rozhodnutí = to appeal against a decision
• odvolat se na zákon = to invoke / refer to the law

In your sentence, the meaning is the legal/official one: to appeal.

Because Czech can leave that unstated if it is already understood from context.

For example, a fuller sentence might be:

• Bez důkazu se nemůžu odvolat proti rozhodnutí. = Without evidence, I can't appeal against the decision.

But if everyone already knows what is being appealed, Czech can simply say:

• Bez důkazu se nemůžu odvolat.

That is very normal.

Putting Bez důkazu first gives it emphasis. It sets the condition first:

• Without proof, I can't appeal.

So the sentence structure highlights the obstacle.

A more neutral order might be:

• Nemůžu se bez důkazu odvolat.

Both are correct, but the given sentence puts special focus on without proof.

Both can work, depending on context.

• proof often suggests something conclusive
• evidence can sound broader and is often natural in legal contexts

So Bez důkazu se nemůžu odvolat could be understood as:

• I can't appeal without proof
• I can't appeal without evidence

Since you already know the meaning, the important grammar point is that Czech uses the singular genitive důkazu after bez.