Learn Hardcore Czech: Syn se dívá na ptáky, kteří sedí na stromech mezi květinami. - My son looks at the birds that are sitting on the trees among the flowers.

dívat by itself is not used in modern Czech with this meaning.
The reflexive pronoun se is part of the verb; you should learn the verb as a whole: dívat se na něco/někoho = to look at something/someone.

So Syn se dívá… is correct and natural.
Syn dívá… is ungrammatical in this meaning.

Why do we say dívá se na ptáky and not just dívá se ptáky?

In Czech, dívat se almost always takes the preposition na for its object:

dívat se na televizi – to watch TV
dívat se na film – to watch a movie
dívat se na ptáky – to look at birds

The pattern is: dívat se na + accusative.
So we must use na ptáky (accusative plural) after dívá se.

What form is ptáky, and why is it not ptáci?

Ptáky is the accusative plural of pták (bird, masculine animate).

Basic forms of pták:

Nominative singular: pták (a bird)
Nominative plural: ptáci (birds – subject of the sentence)
Accusative plural: ptáky (birds – direct object)

Here, ptáky is the object of dívá se na (he is looking at whom/what), so we use the accusative plural: na ptáky.

Why is the relative pronoun kteří used, and not který or které?

The relative pronoun must agree with the noun it refers to in gender and number:

Antecedent: ptáky → from pták, masculine animate, plural.
Relative pronoun for masculine animate plural in the nominative is kteří.

So:

ptáky, kteří sedí… = birds (masc. animate pl.) who/that are sitting…

Other examples for comparison:

lidé, kteří (people who) – masc. animate plural
auta, která (cars that) – neuter plural
květiny, které (flowers that) – feminine plural

What case is kteří in, and why?

In kteří sedí na stromech…, the relative pronoun kteří is:

nominative plural, masculine animate.

It is the subject of the verb sedí inside the relative clause:

(Who is sitting?) → kteří.

So just like in a simple sentence Ptáci sedí na stromech, ptáci would be nominative plural; here kteří stands in that same role inside the clause.

Why is there a comma before kteří?

Czech uses a comma to separate most relative clauses (clauses beginning with který, která, které, kteří etc.) from the main clause.

Main clause: Syn se dívá na ptáky
Relative clause: kteří sedí na stromech mezi květinami

Because the relative clause adds a description of ptáky, we mark the boundary with a comma:
Syn se dívá na ptáky, kteří sedí na stromech mezi květinami.

Why is it na stromech and not na stromy?

The preposition na can take different cases depending on meaning:

na + accusative – motion onto something
- jít na horu – to go onto the mountain
- sednout si na židli – to sit down on the chair (movement to a position)
na + locative – location on/in something (no movement)
- být na hoře – to be on the mountain
- sedět na židli – to sit on the chair (already there)

In our sentence, the birds are already sitting on the trees – a static location, not movement.
So we use na + locative plural: na stromech (on the trees), not na stromy (onto the trees).

What form is stromech, and how does it decline?

Stromech is the locative plural of strom (tree, masculine inanimate).

Basic forms of strom:

Nominative singular: strom
Nominative plural: stromy
Locative plural: (na) stromech

After na with the meaning of static location, we use the locative → na stromech.
So: kteří sedí na stromech = who are sitting on (the) trees.

Why is it mezi květinami and not mezi květiny?

The preposition mezi works similarly to na:

mezi + accusative – motion into / among / between
- jít mezi lidi – to go among people
- vložit něco mezi stránky – to put something between the pages
mezi + instrumental – static position between / among
- stát mezi lidmi – to stand among people
- dům mezi stromy – a house among trees

In this sentence, the trees (and the birds on them) are located among the flowers, not moving into them.
So we use mezi + instrumental plural: mezi květinami (among the flowers), not mezi květiny (into/among the flowers as a direction).

What is the form květinami, and why is it used here?

Květinami is the instrumental plural of květina (flower, feminine).

Basic forms:

Nominative singular: květina
Nominative plural: květiny
Instrumental plural: květinami

Because mezi with a static location takes the instrumental, we say:
mezi květinami = among the flowers.

Can the word order be different, like Syn se na ptáky dívá?

Yes, Czech word order is relatively flexible. All of these are grammatically correct:

Syn se dívá na ptáky, kteří sedí na stromech mezi květinami.
Syn se na ptáky dívá, kteří sedí na stromech mezi květinami. (less natural with that comma, but possible in some contexts)
Na ptáky se dívá syn, kteří sedí na stromech mezi květinami. (again, stylistically marked)

The neutral and most natural version here is the original:
Syn se dívá na ptáky, kteří sedí na stromech mezi květinami.

Changing the order often affects emphasis or style, but not the core meaning. As a learner, stick to the neutral order you see in textbooks until you feel more comfortable.

Why is it just Syn and not Ten syn or Můj syn? How do we know if it is the son or a son?

Czech has no articles like English a/an or the.
The bare noun syn can correspond to:

a son
the son
sometimes even my/our/your son, depending on context.

The exact English translation (a son, the son, my son) depends on context, not on a word in the Czech sentence.

If you want to be explicit in Czech, you can add a determiner:

můj syn – my son
náš syn – our son
ten syn – that/the son (a specific one)

Could we say Syn dívá na ptáky without se and be understood?

No, that would sound incorrect to native speakers.

dívat se na něco is the correct reflexive expression for to look at something.
Without se, dívat is not used in this sense in standard modern Czech.

So the correct form is always dívat se na:

Syn se dívá na ptáky. ✅
Syn dívá na ptáky. ❌ (ungrammatical)

What is the aspect of dívá se? How would we say he will look (once)?

Dívat se is imperfective – it describes an ongoing, repeated, or general action:

Syn se dívá na ptáky. – The son is looking at the birds / looks at the birds (habitually).

The corresponding perfective verb is podívat se:

Syn se podívá na ptáky. – The son will look at the birds (once / briefly).

So:

dívat se → imperfective (process, no built‑in endpoint)
podívat se → perfective (completed act, often future meaning in present tense form).

Are there other verbs we could use instead of dívat se here, and what are the differences?

Yes, you could use other verbs, with slightly different nuances:

koukat (se) na ptáky – to look at/watch birds (more colloquial, informal)
pozorovat ptáky – to observe birds (more deliberate, often more careful watching; no se, usually no na)
hledět na ptáky – to gaze at birds (more literary or formal)

The original dívat se na ptáky is neutral and very common in everyday language, so it’s a good default choice.