Learn Hardcore Czech: Mám s sebou psa.

Mám psa.
– Means “I have a dog / I own a dog.”
– Neutral, general possession (you are a dog owner).
Mám s sebou psa.
– Means “I have a dog with me / I brought my dog (along).”
– It’s about the current situation: the dog is physically with you here and now.

So s sebou adds the idea “with me/with us right now,” not just “I own one.”

Why is there no já (“I”) in Mám s sebou psa?

In Czech, subject pronouns (já, ty, on, ona, my, vy, oni) are usually dropped, because the verb ending already shows the person:

Mám = I have
Máš = you have (singular)
Má = he/she/it has

So Mám s sebou psa already clearly means “I have a dog with me.”
You would add já only for emphasis or contrast:

Já mám s sebou psa, ale on má s sebou kočku.
“I have a dog with me, but he has a cat with him.”

Why is it psa and not pes in this sentence?

Pes is the base (dictionary) form, nominative singular (subject form).

Here, pes is not the subject, it’s the direct object of mám (“I have”).
Mít (“to have”) takes its object in the accusative case:

Nominative (subject): pes – “the dog (does something)”
Accusative (object): psa – “(someone has) the dog”

So:

Pes spí. – “The dog is sleeping.” (subject → nominative)
Mám psa. – “I have a dog.” (object → accusative)
Mám s sebou psa. – same: psa is still the object of mám.

The preposition s governs sebou, not psa, so psa stays in the accusative.

What exactly does s sebou mean, and why isn’t it s mnou (“with me”)?

S sebou literally means “with oneself,” and it’s a reflexive form. It refers back to the subject of the sentence.

Mám s sebou psa. – “I have (with myself) a dog.” → I have my dog with me.
Máš s sebou psa? – “Do you have your dog with you?”
Má s sebou psa. – “He/She has his/her dog with him/her.”

If you said s mnou, it would be a literal “with me,” used in other types of sentences:

Pojď se mnou. – “Come with me.”
On bydlí se mnou. – “He lives with me.”

But for the idea “to have something with you / on you / along,” Czech normally uses mít s sebou (or mít u sebe), not mít s mnou.
“Mám s mnou psa” is incorrect.

Can I say Mám sebou psa without the s?

With the verb mít (“to have”), the natural, standard phrase is:

mít s sebou něco – “to have something with one”

So you should say:

Mám s sebou psa. – correct, natural
Mám sebou psa. – sounds odd / non‑standard to most speakers

However, with some other verbs, especially verbs of taking/bringing, you can find both:

Vzala si knihu s sebou. / Vzala si knihu sebou. – “She took a book with her.”

For a learner, it’s safest to remember:

With mít → mít s sebou
If in doubt, keep the s.

Can I change the word order, e.g. Mám psa s sebou or Psa mám s sebou?

Yes, Czech word order is flexible, and all of these are grammatically possible:

Mám s sebou psa.
– Neutral, typical order. New/important info often goes at the end; here the “dog” is what you’re mentioning.
Mám psa s sebou.
– Slightly more focus on s sebou – perhaps contrasting with a situation where the dog might be somewhere else (at home, in the car, etc.).
– “I have the dog with me (not somewhere else).”
Psa mám s sebou.
– Stronger emphasis on psa – maybe contrasting with some other animal or object.
– “The thing I have with me is a dog.”

In everyday conversation, Mám s sebou psa is the most neutral and common.

How do I say this in the negative or in other persons (you, we, etc.)?

You keep s sebou and just change the verb mít:

Já:
- Mám s sebou psa. – I have a dog with me.
- Nemám s sebou psa. – I don’t have a dog with me.
Ty (singular “you”):
- Máš s sebou psa? – Do you have a dog with you?
- Nemáš s sebou psa. – You don’t have a dog with you.
On/Ona/Ono:
- Má s sebou psa. – He/She has a dog with him/her.
- Nemá s sebou psa. – He/She doesn’t have a dog with him/her.
My (“we”):
- Máme s sebou psa. – We have a dog with us.
- Nemáme s sebou psa. – We don’t have a dog with us.
Vy (plural or polite “you”):
- Máte s sebou psa? – Do you (pl./formal) have a dog with you?
Oni (“they”):
- Mají s sebou psa. – They have a dog with them.

The pattern is: [person of mít] + s sebou + [object in accusative].

Does s sebou change for person or gender (myself, yourself, himself, etc.)?

No. Sebou is the reflexive pronoun in the instrumental case, and it has one form for all persons and genders. The subject and the verb tell you who it refers to:

Mám s sebou psa. – I have a dog with me.
Máš s sebou psa. – You have a dog with you.
Má s sebou psa. – He/She has a dog with him/her.
Máme s sebou psa. – We have a dog with us.
Mají s sebou psa. – They have a dog with them.

For a non‑reflexive “with him/her” (when it’s not the subject), you’d use s ním, s ní, etc., not sebou.

Is sebou always reflexive, or can it mean “with him/her” too?

Sebou is always reflexive – it refers back to the subject of the verb:

On má s sebou psa. – “He has a dog with him (himself).”
Oni mají s sebou psa. – “They have a dog with them (themselves).”

If you want to say “with him/her” where that person is not the subject, you must use a normal pronoun with s + instrumental:

Jdu s ním. – I’m going with him.
Byla tam s ní. – She was there with her.

So sebou never means “with some other person”; it always mirrors the subject.

What case is sebou, and what is it formed from?

Sebou is the instrumental case of the reflexive pronoun sebe (“oneself”).

The reflexive pronoun cases look like this (singular & plural are the same):

Genitive: sebe – (without) oneself
Dative: sobě – to/for oneself
Accusative: sebe – oneself
Locative: o sobě – about oneself
Instrumental: sebou – with/by oneself

With the preposition s (“with”), the instrumental is used:

s kým? → s tebou, s ním, s nimi, s námi, se mnou
s kým? (reflexive) → s sebou

So Mám s sebou psa literally uses “with (s) + oneself (sebou)” in the instrumental.

Could I also say Mám u sebe psa or Mám při sobě psa? Are they the same as Mám s sebou psa?

All three are close in meaning, but there are small nuances and frequency differences:

Mám s sebou psa.
– Very common and natural.
– Neutral “I have a dog with me / I brought my dog along.”
Mám u sebe psa.
– Literally “I have a dog on/at myself.”
– Often used with small objects: Mám u sebe pas. – “I have my passport on me.”
– With psa it’s still understandable and acceptable, just slightly less typical.
Mám při sobě psa.
– More formal or bookish.
– Again, common with documents, money, weapons: Měl při sobě zbraň. – “He had a weapon on him.”
– With a dog, it can sound a bit stiff or unusual in everyday speech.

For everyday spoken Czech about a dog you brought along, Mám s sebou psa is the best choice.

How do you pronounce psa?

Psa is pronounced with both consonants clearly:

Letters: p
- s
  - a
Roughly: ps-ah (one quick syllable)

Tips for an English speaker:

Don’t insert a vowel between p and s (not pə-sa).
Say p and s almost together: like starting to say “psst” and then adding -a.
The a is like “a” in “father,” not like “cat.”

So Mám s sebou psa can be approximated as: maam s-seh-boh psah.