Learn Hardcore Czech: Ano, rozumím ti velmi dobře. - Yes, I understand you very well.

Rozumím ti. – neutral, the normal everyday form.
Rozumím tobě. – emphasizes you, often in a contrast: I understand *you, (not someone else / not something else).*

For example:

Tobě rozumím, ale jemu ne. – I understand you, but not him.

In your sentence, Rozumím ti velmi dobře is the natural choice unless you need contrastive emphasis.

Why does rozumět use the dative case? It feels strange compared to English.

This is a difference in how the two languages structure the idea of "understanding."

In English: understand someone → direct object → accusative idea.
In Czech: rozumět někomu → understand to someone → dative.

Czech treats the person understood as an indirect object:

rozumět komu/čemu (dative)
- Rozumím ti. – I understand you.
- Rozumím českému jazyku. – I understand the Czech language.
- Rozumím tomu. – I understand that.

It’s just a verb–case pattern you need to memorize: rozumět + dative.

Is Ano, with a comma at the start necessary? Could I leave it out?

You can leave out Ano and just say:

Rozumím ti velmi dobře. – I understand you very well.

This is perfectly fine if the context already implies “yes.”

The comma after Ano is standard, because Ano acts like a separate little clause/response, similar to:

Yes, I understand you very well.

So:

Ano, rozumím ti velmi dobře. – fully correct.
Rozumím ti velmi dobře. – also correct, just without the explicit “yes.”

Could I change the word order, for example Ano, velmi dobře ti rozumím or Ano, ti velmi dobře rozumím?

Yes, word order in Czech is flexible, but it changes emphasis a bit.

All of these are grammatically correct:

Ano, rozumím ti velmi dobře. – neutral; light emphasis on how well you understand.
Ano, velmi dobře ti rozumím. – stronger emphasis on velmi dobře (very well).
Ano, ti velmi dobře rozumím. – emphasizes ti (you), as in “You I understand very well (maybe someone else I don’t).”

The most neutral everyday version is your original: Ano, rozumím ti velmi dobře.

What is the difference between rozumím ti and chápu tě?

Both can be translated as I understand you, but the nuance differs:

rozumět (někomu/něčemu) – to understand in terms of language, message, explanation, instructions.
- Rozumím ti. – I understand what you are saying / your words / what you mean.
chápat (někoho/něco) – to grasp, comprehend, get something conceptually or emotionally.
- Chápu tě. – I get you, I understand where you’re coming from (emotionally or intellectually).

So:

In a noisy room: Neslyším tě, ale rozumím ti. – I can’t hear you well, but I understand you.
In a personal conversation: Chápu tě, musí to být těžké. – I understand you, it must be hard.

How would I say this politely to someone I address as vy?

Use vám instead of ti:

Ano, rozumím vám velmi dobře. – Yes, I understand you very well (formal or plural).

Forms:

ti → informal singular you (ty)
vám → formal singular you or plural you (vy)

So to a stranger, a customer, a teacher, etc., use rozumím vám.

Is velmi the only way to say “very”? Could I use moc or hodně?

You can use several intensifiers, but they differ in style:

velmi – neutral, a bit more formal/literary
- Rozumím ti velmi dobře.
moc – very common in spoken language, friendly/informal
- Rozumím ti moc dobře.
hodně – often “a lot,” sometimes instead of “very”; here it sounds a bit less natural
- Rozumím ti hodně dobře. – understandable, but not the most typical.

In everyday speech you’ll hear moc a lot:

Jo, rozumím ti moc dobře.

Why is it dobře and not something that changes with gender, like dobrý/dobrá/dobré?

Because dobře is an adverb (well), not an adjective (good).

dobrý, dobrá, dobré – adjectives; they attach to a noun and agree in gender and case:
- dobrý člověk – a good man
- dobrá kniha – a good book
dobře – adverb; modifies a verb:
- rozumím dobře – I understand well
- mluví dobře – he/she speaks well

Adverbs in Czech do not change with gender or number, so it’s always dobře here, regardless of who is speaking or being addressed.

How do you conjugate rozumět in the present tense?

Present tense of rozumět (to understand):

já rozumím – I understand
ty rozumíš – you (sg., informal) understand
on/ona/ono rozumí – he/she/it understands
my rozumíme – we understand
vy rozumíte – you (pl. or formal) understand
oni rozumí – they understand

Your sentence uses já rozumím (I understand):

Ano, rozumím ti velmi dobře.

Can I replace Ano with Jo or No jo? Are they the same?

They’re similar in meaning but differ in formality and tone:

Ano – neutral, standard, can be used in both formal and informal situations.
Jo – very common in informal speech, like “yeah”.
- Jo, rozumím ti velmi dobře.
No jo – more nuanced: often “yeah, well, yes” with a slight hesitation or resignation, depending on intonation.
- No jo, rozumím ti velmi dobře. – like “Yeah, yeah, I understand you very well.”

For learners, Ano is always safe. Use Jo casually with friends.

How should I pronounce rozumím ti? Any tricky sounds?

Key points:

ro-zu-mím
- r – Czech r is tapped or trilled; the tongue briefly touches the alveolar ridge (just behind the teeth).
- o – short o as in British “lot,” not like English “ou.”
- u – like “oo” in “food,” but short.
- í – long ee; hold it longer: ro-zu-MEEM.
ti – sounds like [tyi], similar to “tyee,” but light and short.
- The t is soft because of i, a bit like the “t” in British “tune” when pronounced carefully.

Stress always falls on the first syllable of each word:

RO-zumím ti
ANO, rozumím ti VEL-mi DOB-ře (always first syllable of each word)