Learn Hardcore Russian: На каникулах мой брат катается на самокате, а сестра ездит на велосипеде. - On vacation my brother rides a scooter, and my sister rides a bicycle.

The base noun is каникулы (holidays, school vacation), which is always plural.
With the preposition на in the meaning “during / on (a period of time)”, Russian uses the prepositional case:
- на каникулах = during the holidays / on vacation (for students)

Approximate declension of каникулы:

Nom./Acc.: каникулы – Каникулы начались. (The holidays started.)
Gen.: каникул – конец каникул (the end of the holidays)
Dat.: каникулам
Inst.: каникулами
Prep.: каникулах – на каникулах

Why is каникулы plural? Can I say it in the singular?

In normal modern Russian, каникулы is used only in the plural (pluralia tantum), very much like English “holidays” in British English.

You say:
- У нас каникулы. – We are on vacation (school/university).
- На каникулах – during the holidays.
A singular form каникула exists historically/poetically, but it’s not used in everyday speech. If you use it, it will sound archaic or odd.

So: treat каникулы as a noun that only has plural forms.

What is the difference between каникулы and отпуск?

Both can be translated as “vacation,” but they are used in different contexts:

Каникулы
- School or university breaks.
- Used about pupils and students.
- Examples:
  - летние каникулы – summer break
  - зимние каникулы – winter break
  - на каникулах – on school/university vacation
Отпуск
- Vacation from work (paid leave, time off).
- Used about adult workers/employees.
- Examples:
  - Я в отпуске. – I’m on vacation (from work).
  - Он поедет в отпуск в июле.

So На каникулах мой брат… implies he is a student/pupil, not a worker on paid leave.

Why is it на каникулах and not в каникулах?

With certain time periods and events, Russian prefers на + prepositional to mean “during / over (this time)”:

на каникулах – during the holidays
на выходных – on/over the weekend
на праздниках – during the holidays/festive days
на Новый год – at New Year (time)

В каникулах is not used and would sound wrong here.

If you want a more neutral phrase “during the holidays,” you can also say:

во время каникул (literally “during the time of the holidays”)

Why is the preposition на also used with самокате and велосипеде?

In Russian, the usual way to say “on / by (a vehicle you ride)” is на + prepositional case:

на самокате – on a scooter
на велосипеде – on a bicycle
на лошади – on a horse
на лыжах – on skis
на коньках – on skates
на машине – by car
на автобусе – by bus

Grammatically:

самокат → prep. sg.: на самокате
велосипед → prep. sg.: на велосипеде

So the preposition на is used here both:

with time: на каникулах
with means of transport / things you ride: на самокате, на велосипеде

Are каникулах, самокате, and велосипеде in the same case?

Yes, all three are in the prepositional case, but:

каникулах – prepositional plural (from каникулы)
самокате – prepositional singular (from самокат)
велосипеде – prepositional singular (from велосипед)

They all follow на + prepositional, but the number (singular/plural) and specific endings differ.

Why is катается reflexive (with -ся), but ездит is not?

Because they come from different verb pairs:

катать – to roll / to give someone a ride (transitive)
кататься – to ride/roll oneself, to go for a ride (intransitive, reflexive)

Кататься always has the reflexive ending -ся / -сь:

он катается
они катаются

By contrast, ездить is originally an intransitive motion verb and doesn’t need a reflexive form:

он ездит
они ездят

So:

кататься на самокате / велосипеде / лыжах – to ride (for fun) a scooter / bike / skis
ездить на велосипеде / машине – to go/ride by bike / car (often as a way of getting somewhere, or as an ability/habit)

What is the difference between кататься and ездить here? Why not use the same verb for both brother and sister?

Both verbs can translate as “to ride,” but they have different nuances:

Кататься (на чём?)

To ride around, usually for fun / recreation, without focusing on a destination.
Typical collocations:
- кататься на самокате
- кататься на велосипеде
- кататься на коньках, на лыжах

Ездить (на чём?)

To go/ride by some means of transport, often with the idea of getting somewhere or as a general ability/habit.
Examples:
- Он ездит на работу на велосипеде. – He commutes to work by bicycle.
- Она плохо ездит на велосипеде. – She doesn’t ride a bike well.

In the sentence:

брат катается на самокате – suggests he is playing / riding around on a scooter.
сестра ездит на велосипеде – can mean she can ride a bike and generally does so; it may be slightly more neutral/practical.

You could also say:

…а сестра катается на велосипеде. This would emphasize that she, too, is riding for fun.

How do these verbs conjugate: кататься and ездить?

Present tense:

Кататься (я катаюсь) – reflexive, 1st conjugation:

я катаюсь
ты катаешься
он/она катается
мы катаемся
вы катаетесь
они катаются

Ездить (я езжу) – 2nd conjugation, irregular stem:

я езжу
ты ездишь
он/она ездит
мы ездим
вы ездите
они ездят

In the sentence:

брат катается
сестра ездит

Does the Russian present tense here work like English “present simple” for habits?

Yes. Russian present imperfective is used for:

Regular / habitual actions:
- Мой брат катается на самокате. – My brother rides a scooter (regularly / as a habit).
General abilities or characteristics:
- Сестра ездит на велосипеде. – My sister rides a bike (knows how to / generally does).

For a specific future occasion, you would normally switch to:

будет кататься, будет ездить (imperfective future for repeated/long action), or
поедет на велосипеде (perfective one-time trip).

Why is the conjunction а used between the clauses, and not и?

Russian has two common “and”-type conjunctions:

и – simple addition: and
а – contrastive “and/whereas/but”

In this sentence:

…мой брат катается на самокате, а сестра ездит на велосипеде.

А highlights that:

the brother does one activity (scooter),
whereas the sister does a different activity (bicycle).

Using и would sound less contrastive and more like just listing two things:

…мой брат катается на самокате, и сестра ездит на велосипеде. This is not wrong, but it slightly weakens the “brother does X, but sister does Y” contrast.

Why do we say мой брат, but just сестра (without моя)? Is моя сестра possible?

Yes, моя сестра ездит на велосипеде is absolutely correct.

In the original sentence:

На каникулах мой брат катается на самокате, а сестра ездит на велосипеде.

Once мой брат is mentioned, it is clear we are talking about family members. In Russian, when the possessor is obvious (my, our, his, etc.), the possessive pronoun is often omitted to avoid repetition:

Мой брат и сестра живут в Москве. – My brother and (my) sister live in Moscow.

So:

Both а сестра ездит… and а моя сестра ездит… are grammatically correct.
The version without моя is simply shorter and more natural here.

Is the word order “На каникулах мой брат…” important? Could we say “Мой брат на каникулах катается на самокате”?

Word order in Russian is relatively flexible. All of these are grammatically possible:

На каникулах мой брат катается на самокате.
Мой брат на каникулах катается на самокате.
Мой брат катается на самокате на каникулах.

The differences are mainly in emphasis:

Starting with На каникулах puts the time frame in focus: During the holidays, my brother rides a scooter…
Starting with Мой брат focuses more on the person: My brother, during the holidays, rides a scooter…

The original order is very natural and common: set the time first, then say what people do during that time.

How are the main content words stressed and pronounced?

Approximate stresses (stressed syllables in caps):

на кани́кулах – na ka-NI-ku-lakh
(stress on НИ)
мо́й брат – MOY brat
(stress on мой only syllable)
ката́ется – ka-TA-ye-tsa
(stress on ТА)
самока́те – sa-ma-KA-te
(stress on КА)
сестра́ – sis-TRA
(stress on ТРА)
е́здит – YEZ-dit
(stress on ЕЗ)
велосипе́де – ve-la-si-PE-de
(stress on ПЕ)

Getting the stress right is important, because changing stress often changes the word’s form or even its meaning in Russian.