If i understand you correctly, you not understand when we use svůj, svá, ...
Well unlike english people we do not use posessive pronouns with every noun. Mostly we just omit them. For example: English: I closed my eyes X czech: Zavřel/a jsem oči (I did it so it is clear that the eyes were mine.)
In sentences where the posessive pronoun is needed we usually do not say můj, tvůj...but svůj. Svůj means something like my own, his own, ... Like here. "I am thinking about my girl." - you can say "Myslím na mou/moji dívku." but it sounds unnatural and it is better to say: "Myslím na svou/svoji dívku." (Svou/svoji are just two variants of one word)
I hope you don't mind me using your sentence and adding a couple more examples with just that one sentence. I hope I made no mistakes in these.
JÁ: Já myslím na svoji dívku. [I - my] / Myslím na tvoji dívku. / Myslím na jeho dívku. / Myslím na naši dívku. / Myslím na vaši dívku. / Myslím na jejich dívku.
TY: Myslíš na moji dívku? Ty myslíš na svoji dívku? [You sg. - your sg.] Myslíš na jeho dívku? Myslíš na naši dívku? Myslíš na vaši dívku? Myslíš na jejich dívku?
ON: Myslí na moji dívku. Myslí na tvoji dívku. On myslí na svoji dívku. [In this sentence he thinks about his own girl.] On myslí na jeho dívku. [In this sentence he thinks about another guy's girl.] Myslí na naši dívku. Myslí na vaši dívku. Myslí na jejich dívku.
MY: Myslíme na moji dívku. Myslíme na tvoji dívku. Myslíme na jeho dívku. My myslíme na svoji dívku. [we - our] Myslíme na vaši dívku. Myslíme na jejich dívku.
VY: Myslíte na moji dívku. Myslíte na tvoji dívku. Myslíte na jeho dívku. Myslíte na naši dívku. Vy myslíte na svoji dívku. [you pl. - your pl.] Myslíte na jejich dívku.
ONI: Myslí na moji dívku. Myslí na tvoji dívku. Myslí na jeho dívku. Myslí na naši dívku. Myslí na vaši dívku. Oni myslí na svoji dívku. [They think about their own girl.] Oni myslí na jejich dívku. [They think about a girl of "some other people".]
Thank you very much ValaCZE and Jamie. So if I have understood, Myslím na svoji dívku means "I think about MY OWN girl" ; Myslíš na svoji dívku means "You think about YOUR OWN girl". Ecc. In other words, if we can put "own" after the possessive pronoun, instead of using their specific forms (with "dívku would be:moji,tvoji, její/jeho, naši,vaši,jejich) we always use "svoje"(dívku). Did I say right? Thanks again for all the enormous help!
I had the same question some time back. One of the volunteers solved The Mystery for me this way (although this isn't an exact quote):
If the SUBJECT of the sentence also POSSESSES THE OBJECT of the sentence, then "svůj" (with the appropriate gender and case endings) would be the possessive pronoun to use.
Unfortunately, I don't recall who answered my question, because I would like to credit him or her... it was very helpful to me!
In that case, could you give some examples where the subject (me) does NOT possess the object, but still uses 'my' (moji/moje etc)? You already mentioned above that body parts ('my eyes') would use no possessive at all, while 'my girl' is, a bit creepily, able to be thought of as a possession (although I get it is 'my own, as opposed to yours'). In the earlier parts of this unit, when we learnt about my dog, my horse etc with moji/moje, is that a natural use of 'my' or would svuji/svuje be more common?
I am learning, too, so you may get a more authoritative answer from one of the native Czech speakers on the team. As I understand it, it is not wrong to use můj (etc.) in these cases (where the subject "owns" to object), but the use of svůj may be more common... maybe just because Czech has it, and English doesn't. :-)
Slavic peoples cannot use in an informal way words my car, your wife in a possesive way. "You have your car" Ти маєш свою машину - ty maiesh svoiu mashynu. Slavic peoples don't like doublage of you/your, I/my, he/his, she/her in one sentence. So we change them on these words (In my natuve Ukrainian свiй, своя, своє, своï)
Ah, thank you! I think your explanation is very similar to those of @ValaCZE and @Jamie08MD but I didn't quite understand their explanation and the long list of examples earlier but now I do! Thank you for willing to repeat what others have written in a different way.
Thank you also for reminding me very clearly how other Slavic languages can be similar to each other. And it's nice to see some Cyrillic letters again! =)