Source: Because the Torah writes "Lo Yuchal Ba'alah ha'Rishon Lashuv Lekachtah". This is the text according to Rashi.

Refuted Text: He did not have the text 'Derech Havayah Asrah Torah' ...

Reason: ... because from the Lashon 'Havayah' the Gemara learned earlier that someone who takes back his divorced wife is only Chayav via Bi'ah, whereas now we are learning that he is only Chayav even if he only betrothed her.

Reinstated Text: It is possible however, to accept the text 'Derech Havayah Asrah Torah' ...

Reason: ... because earlier, the Gemara learned it from "le'Ishah", whereas now it is Darshening from "Lih'yos", which implies 'Havayah' - which in turn, is synonymous with Kidushin.

Clarification: ... of Chalal and a first generation Mitzri.

Question: According to Rebbi Yossi, why does the Mishnah validate the daughter of a Ger? It ought to have declared her Pasul due to the 'Mah ha'Tzad' of Chalal and Mitzri Rishon, like Rebbi Yehudah holds?

Answer #1: We must say that Rebbi Yossi does not consider this a Tzad ha'Shaveh to declare Pasul a bas Ger based on it ...

Reason: ... bearing in mind that the daughter of a Chalal is not forbidden to enter into the congregation of Yisrael, whereas a first generation Mitzri is ...

Answer #1 (cont.): It is therefore not possible to say 'ha'Tzad ha'Shaveh she'bahen she'Einan be'Rov Kahal u'Bito Pesulah' - seeing as the P'sul of the daughters is not the same.

Answer #2: Moreover, it is a Dochek to interpret 'Eino be'Rov Kahal' by the one, to mean that there is an aspect of sin, and by the other, that he is Pasul to enter the Kahal.

Reason: It is not logical to say this since they are not equivalent.

Introduction to Question: The Ri asks that - the P'sul Bi'ah of a Mitzri is only applicable where he marries a bas Yisrael ...

Reason: ... since a Mitzris is already Pasul ...

Question: ... in which case one can query the Tzad ha'Shaveh in that there is an aspect of sin, as the Gemara asked above ... Tosfos Yeshanim].

Explanation #1: ... because the Torah writes "Almanah Lo Yikachu", Rashi explains, whereas the Seifa speaks about a Kohen Hedyot, since it says "mi'Zera Yisrael", and we Darshen that her Besulim were 'sown' - which speaks about all Kohanim.

Question: But "mi'Zera Yisrael" refers to a Kohen Gadol no less than to a Kohen Hedyot?

Explanation #2: What it therefore means is 'Reisha be'Kohen Gadol - since it writes "Almanah u'Gerushah Lo Yikachu ki im Besulos", which applies exclusively to a Kohen Gadol ...

Explanation #2 (cont.): ... whereas the Seifa of the Pasuk writes "ve'ha'Almanah asher tih'yeh Almanah mi'Kohen Yikachu" - which speaks exclusively about a Kohen Hedyot.

Explanation #1: Rashi explains that, had the Torah not believed the father to acknowledge his son, the latter would not have acquired the property due to a 'Migu that he could have given it to him anyway' ...

Explanation #1 (cont.): ... because even Rebbi Meir, who holds 'Adam Makneh Davar she'Lo Ba le'Olam', concedes that if someone who says 'The property that I will obtain after I become a Goseis will be yours' has said nothing ...

Reason: ... since at the time that he obtains it he is not capable of giving a Matanah - because he holds that the Matanah of a Goseis is not valid ...

Explanation #1 (concl.): ... but where he comes because of the Bechorah , it is valid.

Implied Question: And the reason that he mentions 'Goseis' and not 'property that fell to him after death' is ...

Answer: ... because even with regard to the Bechorah his words would not then be valid, seeing as a B'chor does not receive what is 'Ra'uy' as he does what his deceased father already owns ...

Answer (cont.): ... and this is Ra'uy, since when he died, it was not yet in his possession, and the Torah writes "be'Chol asher Yimatzei lo".

Inference: Rashi's explanation implies that what a Goseis gives is not valid.

Precedence: Likewise some commentaries learn that if a Goseis hints that one should write his wife a Get, one does not comply, since the acts of a Goseis are not valid.

Question: But in the first Perek in Erchin (Daf 6b) the Gemara says that 'A Goseis is considered a live person in all regards - his Neder is s Neder and his Hekdesh is Hekdesh'.

Answer: One can refute this proof however, in that Davka there in connection with a Neder and Hekdesh (we say that) since one applies the principle "A word to Hekdesh is like handing over to a Hedyot', but not elsewhere.

Question #1: The Kashya remains however, from Perek Mi she'Achzo (Gitin, Daf 70b), where the Gemara rules that 'If somebody slit someone's two Simanim or the majority of two Simanim, and the latter then hinted that one should write a Get and hand it to his wife, they should comply ...

Question #1 (cont.): ... and there is no bigger Goseis than that, since he is bound to die?

Introduction to Question #2: Also in Perek Kol ha'Get (Ibid., Daf 28 a) the Gemara rules that if someone brings a Get from overseas, where he left the husband an old man or a sick one, he should hand over the Get on the assumption that he is still alive ...

Introduction to Question #2 (cont.): ... and Rava there comments that that speaks specifically where he left the husband a sick man, but where he left him a Goseis, he may not hand it over, since we are afraid that he may have died ...

Introduction to Question #2 (concl.): ... implying that if we would know for sure that he was still a Goseis, he would hand it over knowing that he is alive, and the Get would be valid ...

Question #2: So we see that what a Goseis does is valid?

Explanation #2: Therefore Tosfos explains that the acts of a Goseis are certainly valid, and the reason that, in our case, his Matanah is not is ...

Explanation #2 (cont.): ... because presumably the Goseis is unable to talk - but if he would be, it is obvious that his words would be valid.

Implied Question: And the reason that it mention 'Goseis' and not 'A sick person who is unable to speak' is ...

Answer: ... because the latter will probably get better and he will then be able to be Makneh ...

Explanation #2 (cont.): And also if a sick person who cannot speak nods his head this too is valid (Gitin 67b & 71a).