In Bavli Shabbos 6a, the four domains of Shabbat are listed as:
- reshus hayachid
- reshus harabbim
- mekom petur
Thus, we read:
Our Rabbis taught: There are four domains in respect to the Sabbath; private ground, public ground, karmelith, and a place of non-liability. And what is private ground? A trench ten [handbreadths] deep and four wide, and likewise a wall ten [handbreadths] high and four broad, — that is absolute private ground.9 And what is public ground? A highroad,10 a great public square,11 and open alleys,12 — that is absolute public ground. One may not carry out from this private to this public ground, nor carry in from this public to this private ground; and if one does carry out or in, unwitting, he is liable to a sin-offering; if deliberately, he is punished by kareth13 or stoned.14 But the sea, a plain, a colonnade, or a karmelith, ranks neither as public nor as private ground:15 one must not carry [objects] about16 within it and if he does, he is liable; and one must not carry out [an object] thence into public ground or from the public ground into it, nor carry [an object] from it into private ground or from the private ground into it; yet if he does carry out or in, he is not liable. As to courtyards with many owners17 and blind alleys,18 if an 'erub is made, they are permitted; if an 'erub is not made, they are forbidden.19 A man standing on a threshold20 may take [an object] from the master of the house, or give [it] to him, and may take [an object] from the poor man or give [it] to him; providing however that he does not take from the master of the house and give to the poor man or from the poor man and give it to the master of the house;21 and if he does take and give, the three are exempt. Others state, A threshold serves as two domains: if the door is open, it is as within; if shut, it is as without. But if the threshold is ten [handbreadths] high and four broad, it is a separate domain.22
The example of the threshold is one of mekom petur. Yet it seems to introduce a completely new topic and paragraph. And it details a man standing on a threshold, rather than a domain: a threshold. This does not fit the pattern.
And what of the courtyards with many owners and blind alleys, which is a description of a domain? I suppose it can be classified as a type of karmelit, but it has its special rules for rendering it exempt. Certainly it should be listed as such?
If we look in the Yerushalmi Shabbos 5a, this is what we find:
ארבע רשויות לשבת. רשות היחיד. רה"ר. וכרמלית. ומבואות שאינן מפולשין. ואיזהו רה"י. חריץ שהוא עמוק עשרה ורחב ארבע. וגדר שהוא גבוה עשרה ורחב ארבע זו היא רשות היחיד גמורה. ואי זהו רשות הרבים גמורה. איסטרטייא ופלטיא ומדבר ומבואות המפולשין. אין מוציאין מרה"י לרה"ר ולא מכניסין מרשות הרבים לרשות היחיד. ואם הוציא או הכניס שוגג חייב חטאת. מזיד
It terms of reshus hayachid gemura:
The Master said: 'That is [absolute] private ground.' What does this exclude?23 — It excludes the following [view] of R. Judah. For it was taught: Even more than this did R. Judah say: If one owns two houses on the opposite sides of the street,24 he can place...
If we say that this gemura is meaningful (as opposed to the one for reshus harabbim gemura), then we can say, on a peshat level, that one might not have thought that these actually rose to the level of private domain. Consider the cases:
And what is private ground? A trench ten [handbreadths] deep and four wide, and likewise a wall ten [handbreadths] high and four broad, — that is absolute private ground.9
How about a house, with four walls, a door, and a roof? This is surprisingly not listed as a reshus hayachid. That is because the brayta is saying that each of these "flimsier", halachically defined domains, already rise to the level of a private domain. And certainly a hope would rise to that level as well.
The Master said: 'That is [absolute] public ground.' What does this exclude? — It excludes R. Judah's other [ruling]. For we learnt: R. Judah said: If the public thoroughfare interposes between them, it must be removed to the side; but the Sages maintain: It is unnecessary.7 And why is it called 'absolute?' — Because the first clause states 'absolute', the second does likewise.
So we should not derive anything from the word gemurah in the second instance.
Actually, on a peshat level, here is the reason for the word gemura for both the reshus hayachid and reshus harabbim. In the brayta, and in the Tosefta, the continuation is:
א,ב אבל הים והבקעה [והכרמלית] והאסטוונית והאסקופה אינן לא [רה"י ולא רה"ר] אין נושאין ונותנין [לתוכן] ואם נשא ונתן פטור אין מוציאין לא מתוכן לרה"ר ולא מרה"ר לתוכן ואין מכניסין מתוכן לרה"י [ומרשות] היחיד לתוכן ואם הוציא והכניס פטור חצר של רבים ומבואות שאין מפולשין עירבו מותרין לא עירבו אסורין.
Note the bracketed text I bolded and marked in red. The yam, bika, karmelis, etc., are not like either reshus harabbim or reshus hayachid. They are not for public thoroughfare and they are not enclosed. This is what gemura is coming to exclude, on a peshat level.