Rambam - 3 Chapters a Day

Introduction
Deuteronomy 21:18-21 states: If a person will have a wayward and rebellious son who does not heed the voice of his father or the voice of his mother and they chastise him, but he does not heed them. His father and mother shall take hold of him and bring him out to the elders of his city and to the gate of his place. They say to the elders of his city: “This son of ours is wayward and rebellious. He does not heed our voice; he is gluttonous and a lush.” All of the men of his city will clout him with stones, killing him, and you shall remove evil from your midst. All Israel shall hear and fear.
Our Sages (primarily in Sanhedrin 68b ff.) interpret this passage precisely, explaining how each term used in the passage teaches us a different concept. In the chapter that follows, the Rambam summarizes and organizes their teachings, giving us a clear-cut picture of the requirements of the mitzvah. It is important to emphasize that there is a difference of opinion among our Sages if the judgment of “a wayward and rebellious son” ever took place (Sanhedrin 71a). Some maintain that such a judgment was never issued. Indeed, from all the particulars mentioned by the Rambam, one can understand that it could be impossible for such a judgment to have been issued. Others maintain that they know of an instance where an individual was executed because of this transgression.
Sanhedrin 72a asks: Is eating the gluttonous meal (to be described by the Rambam) a sufficient cause for a person to be executed? In resolution, our Sages explain that the Torah considered the ultimate fate of such a person. He will be drawn after his natural tendencies and continue to steal and eat gluttonously. Ultimately, he will become a robber and slay people in order to support his habit. It is preferable, the Torah maintains, for him to be executed early in life, before he commits such severe sins.

Sefer HaMitzvot (negative commandment 195) and Sefer HaChinuch (mitzvah 248) include the commandment not to act as “a wayward and rebellious son” as one of the 613 mitzvot of the Torah.

For if it is expensive, it is unlikely that he will develop a habit of eating and drinking in this manner.

Who eat hurriedly lest they be detected and do not wait for their food to cook.

I.e., thinned, but not thinned in the manner that wine was ordinarily consumed. In the Talmudic era, the wines were very strong and it was customary to add water, even as much as three times the measure of the wine itself, to the wine before partaking of it.

According to Shiurei Torah, this would be approximately 200 grams, and 350 grams according to Chazon Ish.

Half a log is slightly more than 172 cc according to Shiurei Torah and 300 cc according to Chazon Ish.

The Radbaz interprets this as meaning in one mouthful. This is what is implied by the expression “eating ravenously” mentioned in Halachah 1. He states that it is possible for this to happen with regard to drinking, but it is almost impossible for a person to put that much meat in his mouth at one time. Therefore he interprets it to mean “without interruption, as if it were one mouthful, that before swallowing the first portion, he stuffed the second in his mouth.”

This implies that he is afraid that his father will notice him. Since he still has a sense of shame, it is not as likely that he will become habituated to stealing. Accordingly, it is less likely that he will ultimately become a robber and murderer (Kessef Mishneh).

It will not always be possible for him to steal from others. Hence, since the habit will not be as strongly ingrained in his personality, it is possible that he will not rob and murder (Ibid.).

E. g., a meal honoring a circumcision or a marriage of which it is a mitzvah to partake.

E. g., the food or wine was not kosher.

For the phrase can be interpreted: “He does not heed our voice alone,” i. e., they are not complaining that their son is transgressing the commandments, only that he is rebelling against them (Radbaz).

For that phrase can also be interpreted as implying “he heeds neither our voice or God’s voice.” Hence when he partakes of the meal while heeding God’s voice, he is not liable. Alternatively, since he is performing a mitzvah while partaking of the food, his actions may not become habitual (Radbaz). The Kessef Mishneh suggests that this second clause is in fact the start of the following paragraph.

For eating the second tithe in the holy city fulfills a mitzvah.

See Hilchot Evel 13:8.

Which are forbidden.

I.e., the meat of a domesticated animal. With regard to the meat of a wild animal, e.g., deer, there is a debate among the later authorities; some hold him liable and some do not.

At which point the flavor of the salt overpowers the flavor of the meat.

Which has not fermented and has no alcoholic content. One opinion in Sanhedrin 70a interprets this as referring to grape juice that has not been left to ferment for 40 days.

I.e., a boy below the age of thirteen.

For the Torah refers to him as a "wayward and rebellious son," i.e., a son and not a man (Sanhedrin 68b).

This is the sign of physical maturity which when manifested indicates that a child has attained maturity.

But not the entire genital area (Kessef Mishneh).

As stated in the following halachah, we are speaking about a period of three months or less.

It takes, however, three months before the fetus reaches a size when it could be recognized. See Genesis 38:24. The Radbaz notes that there are situations where a fetus can be recognized before three months have passed, but this. is not the norm. And the ruling follows the majority.

As stated in the previous halachah.

Who have been granted semichah.

As stated in Deuteronomy 21:20.

For lashes are not administered unless a warning is given.

See Hilchot Sanhedrin chs. 16-17.

Note the Kessef Mishneh who asks why an examination is not made before the youth is lashed. For if he is too old to be classified as a “wayward and rebellious son,” there is no reason that he be lashed either.

I.e., although they brought him to court and initiated proceedings against him, in the midst of the trial, their mercies overwhelmed them and they forgave him. If, however, he already had been sentenced, he is executed even if his parents desire to forgive him.

For his body has undergone a change and he would not be held liable for this act in his present state.

He is not even given the first set of lashes (Or Sameach).

I.e., both acting together in agreement.

The Meiri states that these people have a tendency to cruelty. Hence, they may not condemn their sons in this manner. The verses are merely asmachteot.

The expression “This” implies something that you can point your finger at and say: “This is it” (Rashi, San. 71b).

This reply implies that they hear his obstinate replies to their statements to him (Ibid.).

As stated in the introduction to this chapter, a “wayward and rebellious son” is executed because of his ultimate future. We fear that he will become habituated to stealing, eating, and drinking and will ultimately become a robber and murderer. Since it is less likely for a woman to develop such habits, she is nor judged in this manner.
The commentaries note that in Sanhedrin 69b-70a, Rabbi Simon states that a girl may develop such tendencies and support her habit through prostitution. They question why the Rambam does not mention this point. The Kessef Mishneh uses this as a proof that the command to kill “a wayward and rebellious son” is a Torah decree above the bounds of intellect.

A person whose genital area is covered with a block of flesh and whose gender cannot be determined.

A person with both male and female sexual organs.

I.e., after he was apprehended for stealing and participating in such a feast. It would appear that if the operation is performed beforehand, he is like any other male. There are, however, authorities who do not accept this conception. They even cite manuscript copies of the Mishneh Torah which read “from [the beginning of]s existence” instead of “at the time he receives the warning.” The latter opinion is reflected in the wording of the Rambam’s source (Bava Batra 126b).

I.e., his masculinity must be obvious.

For the passage concludes (Deuteronomy 21:21): “All Israel shall hear and fear.” The announcement is circulated after the execution.

Compare to similar statements in Hilchot Edut 18:7.

See Hilchot Evel 1:9.

For the “wayward and rebellious son” has no closer heir. We do not fear that he will have him executed because he desired to inherit his estate (Radbaz).

I.e., there are two dimensions of this mitzvah: a) for any person to mourn for his relatives; b) that despite the impurity involved, a priest must be involved in the burial of his relatives.

I.e., on the surface, these mitzvot are not directly related to the subject matter of this book, "The Book of Judges." Nevertheless, because of the connection mentioned by the Rambam, it is more appropriate to discuss these mitzvot here than in any other place in the Mishneh Torah.

See Hilchot Sanhedrin 15:8 where this mitzvah is discussed.

Sefer HaMitzvot (positive commandment 37) and Sefer HaChinuch (mitzvah 264) count this as one of the 613 mitzvot of the Torah. There are, however, other Rishonim who do not accept this concept. The Shulchan Aruch (Yoreh De’ah 398:1) quotes both these views, while the Ramah (Yoreh De’ah 399:13) states that the common practice is to follow the opinion that there is no Scriptural obligation for mourning. Among the distinctions between these two views is whether there is an obligation to mourn on the second day of a festival or not.
In Chapter 2, Halachah 1, the Rambam defines the term “[close] relatives” as one’s “father, mother, son, daughter, brother, and sister.” As will be explained there, others also include one’s spouse.

Aaron posed this question to Moses after Moses asked him why he did not partake of a sin offering despite the fact that Aaron's sons had died that day. The Rambam maintains that the fact that mourning for his sons took precedence over partaking of the sacrifices which is a mitzvah indicates that mourning is also a mitzvah (Radbaz).
The Kessef Mishneh notes that this is a somewhat indirect commandment and notes that in Sefer HaMitzvot, loc. cit., the Rambam quotes another source. There, he states that the mitzvah is derived from the priests’ obligation to become impure while caring for their deceased close relatives.

I.e., according to the Rambam, for there to be a Scriptural obligation of mourning, the death and the burial must be on the same day.

Joseph instituted mourning for Jacob.

I.e., when there is a difference between the two, our conduct follows the commandments given at Sinai and not the conduct of the Patriarchs and their descendants.

I.e., although the observance of these seven days is a Rabbinic institution. Chronologically, it was given to the Jewish people at the same time as the Scriptural commandments.

We have translated the Rambam’s words loosely. The term golal refers to a large stone which is placed over a grave to close it. See the Rambam’s Commentary on the Mishnah (Ohelot 2:4).

See Chapter 5, Halachah 1. There are, however, certain obligations incumbent upon him because of the state of aninut. See Chapter 4, Halachah 6.

II Samuel, ch. 12, relates that when the first son whom Bathsheba bore David became ill, David oppressed himself, ­buried.

In the Talmudic era, it was very common for the Romans to crucify people and leave their bodies unburied. The Kessef Mishneh states that if it is possible to bribe the ruling authorities to allow the corpse to be buried, then the mourning rites cannot be started.

For it is unlikely that they would be successful in stealing the corpses.

The Radbaz notes that the Rambam’s wording leaves unclarified a question raised by other Rabbis. To explain: As stated in Hilchot Gerushin 13:16, if a person drowns in water that does not have definite boundaries, a sea or the ocean, his wife is not given the chance to remarry. There are authorities who maintain that in such a situation, mourning rites should also not be held. For if one holds mourning rites, people will be certain that he died and his wife will be allowed to remarry. This opinion is reflected in the ruling of the Shulchan Aruch (Yoreh De’ah 375:7). The Radbaz, however, does not accept this conception entirely. He explains that, according to the Rambam, since mourning is a Scriptural obligation, it should not be overridden because of the possibility of such an error.

The Shulchan Aruch (loc. cit.) states that if, after the family despaired of finding the corpse and held mourning rites, the corpse is discovered, there is no need to hold mourning rites again. The deceased’s sons, however, should mourn for the remainder of the day on which the corpse was discovered.

Kin’at Eliyahu notes that today, with the advances in modern communication, it is possible to know when a corpse was buried even when it is buried in a distant place. Hence the mourners in distant places do not start the seven days of shivah mourning until the burial.

The people who accompany the corpse, by contrast, are obligated to begin mourning rites only after the burial. Thus two members of the family may complete mourning rites for the same person on different days.

Nor should a priest become impure (Chapter 2, Halachah 8).

In contrast to an animal which is considered as viable after eight days (Shabbat 135b).

The Radbaz states that this applies even when the fetus dies of unnatural causes, e.g., it is consumed by a beast of prey. Since we are not certain that the birth was viable and thus we are obligated to mourn, we follow the more lenient position.

I.e., the woman did not engage in relations with her husband from nine months before the child's birth until her pregnancy was detected [Rashi, Shabbat 136a; Shulchan Aruch (Yoreh De'ah 37:8)].

When a pregnancy continues for its full term, we assume that the birth was viable and that the infant died for other reasons. Compare to Hilchot Rotzeach 2:7.
The Ramah (Even HaEzer 156:4) writes that in the present era, as long as we know that a woman has reached her ninth month of pregnancy, her child is considered as viable. Hence the mourning rites would have to be observed for such an infant.

The Ra’avad differs with the Rambam and maintains that we do observe mourning rites for a child born in the eighth month if it survives for more than 30 days. The difference between them depends on our Sages’ statement (Shabbat 135a) that an infant born in the eighth month is like a stone; i.e., it will certainly die and therefore it may not be carried on the Sabbath. The Ra’avad maintains that if the infant lives 30 days, it becomes obvious that it was in fact a fetus from a seven month pregnancy that remained in the womb somewhat longer and the birth is considered viable. The Rambam does not accept such a possibility. (It must be emphasized that today, efforts are made to save all infants, even those born in the eighth month and in many instances, the doctors have been successful in enabling such infants to live.)

I.e., we do not arrange eulogies and funeral processions. We do, however, arrange for the fetus' burial (Siftei Cohen 344:6). There are, however, opinions (Hagahot Maimoniot, Hilchot Milah 1, note 10) which maintain that there is no mitzvah in burying a stillborn fetus.

I.e., even though the Torah granted such license, these individuals are not considered like those executed by the court. Kiryat Melech cites proof from II Samuel 11:27 which speaks of Bathsheba mourning for her husband Uriah even though he was killed as a rebel against the king.

I.e., the funeral and eulogies should be held in an ordinary manner. Since their transgression involved disobeying the ruling authorities, their death is sufficient to atone for that transgression.

In punishment for rebelling against him.

See Hilchot Sanhedrin 13:6. The severity of their transgressions is so great that the additional measure of withholding mourning rites is necessary for them to gain atonement (see Sanhedrin 46b and commentaries). In his Commentary to the Mishnah (Sanhedrin 6:8), the Rambam writes that the atonement for these individuals is not granted until their corpses begin to decompose. Hence at the time of the funeral, it is not fit to mourn for them. See also Chapter 2, Halachah 8.

See Chapter 4, Halachah 6.

I.e., it is not an expression of honor for the departed and thus withholding it will not bring him atonement (see Sanhedrin, loc. cit., and commentaries).

For we do not bury a wicked person next to a righteous one. When, however, their corpses have decomposed that is a sign that their sins have received atonement (ibid.). See Hilchot Sanhedrin 14:9.

See Hilchot Mamrim 3:2 for further explanation of these terms.

As Proverbs 11:10 states: “At the devastation of the wicked, there is rejoicing” (Siftei Cohen 345:9).
Although this law is quoted by the later authorities [Shulchan Aruch (Yoreh De’ah 345:5)], in all ages, there were Rabbinic authorities who differed. For example, Rabbenu Gershom had a son who converted and yet, that sage mourned for him. (Indeed, he mourned 14 days.) Even the authorities who maintain that this practice should be upheld with regard to the deviants themselves, rule more leniently with regard to their descendants [see Ramah (Yoreh De’ah 340:5)]. Since they were raised without a full awareness of their Torah tradition, they are not judged as seriously for their violation of it. On this basis, there are many contemporary authorities who counsel leniency with regard to holding mourning rites for Reform and Conservative Jews today.

We do not even rend our garments in mourning or attend his funeral.

For suicide is considered a grave sin, equivalent to murder (see Bava Kama 91b). Hence, any act that is a token of respect for the deceased is withheld. Although mourning on the first day fulfills a Scriptural commandment, that commandment applies only when the deceased is an observant member of the Jewish community (Radbaz).

See Chapter 13, Halachah 1.

See Chapter 12, Halachah 7.

For they have suffered a loss and their feelings should be assuaged.

For perhaps he slipped and fell accidentally.

I.e., he states his intention to commit suicide.

Even though the circumstantial evidence would appear to lead to the conclusion that he committed suicide, we do not act upon that conclusion.

I.e., he is given a full eulogy, funeral procession, and mourning rites.
The Shulchan Aruch (Yoreh De’ah 345:3) states that a person who commits suicide because he is forced to for example, King Saul, should be mourned.
In practice, the issue is very delicate and in many instances, even when there is much circumstantial evidence that a suicide was voluntary, Rabbis have allowed mourning rites to be held.

Leviticus 21:2-3 mentions that a priest is obligated to become impure while tending for the corpses of these individuals. Mo‘ed Kattan 20b states: “Whenever a priest is obligated to become impure, others are obligated to mourn.”

One’s mother is mentioned first, because she is mentioned first in the verse.

See Halachah 12 on which basis we can appreciate why the Scriptural obligation is only for paternal siblings.

The verses from Leviticus cited above mention: shaaro hakarov eilav which Yevamot 22b interprets as referring to one’s wife. The Rambam, however, maintains that this is merely an asmachta, a Rabbinic Law associated with a Scriptural verse, and not the direct meaning of the verse. This interpretation is borne out by the translation of the verse by Onkelos (see Halachah 6). Similarly, when the prophet Ezekiel describes the obligation for the priests to become impure (44:25), he mentions the other six relatives and not the priest’s wife. Nevertheless, there are other authorities who follow the interpretation in Yevamot. The Kessef Mishneh explains that the Rambam is following a principle which. he stated on several occasions: Any concept derived through the principles of Biblical exegesis is described as Rabbinic in origin although it has the strength of Scriptural Law.

If, however, she has been merely consecrated, he is not required to mourn (Halachah 3). Needless to say, if he has divorced her; he is under no obligation.

For it is appropriate to express feelings of grief for the loss of any close relative (Radbaz).

According to Rabbinic decree.

For whom he may not become impure, as stated in Halachah 10.

The Ramban, the Kessef Mishneh, and many other authorities have questioned the Rambam’s ruling in this halachah. The Merkevet HaMishneh offers a possible explanation, stating that the obligation to become impure on behalf of a corpse is to insure that someone takes care of that corpse’s burial (see Halachah 6). For if the deceased’s close relatives do not bury him, who else will? With regard to a married woman, however, there is no such fear, for her husband is obligated to bury her. Hence, no license is granted for her brothers to become impure on her behalf. On the other hand, they are obligated to mourn.

For the child's natural father is not considered as his father from a halachic perspective and thus the two share no family ties (Yevamot 22a).

For a convert (and a freed servant) is considered as a newborn infant with no ties to his natural parents (ibid.).

According to Jewish law, marriage is a two stage process involving: a) erusin - consecration, when the marriage bond is established and the woman becomes forbidden to all other men, and b) nisu’in- marriage, when the couple begin living together as man and wife. Although at present, both of these stages commence on the same day, in Talmudic times, couples would wait a substantial period between the two.
As stated in Halachah 7 and notes, a priest does not become impure for such a wife. Hence, other men are not required to mourn.

Who is no longer his wife because he divorced her.

This is simply a measure of respect.

E. g., when one’s grandfather dies, one observes mourning rites while together with one’s father and when one’s nephew dies, one observes mourning rites while together with one’s brother.
The Ra’avad takes issue with the Rambam. Although he agrees that this principle applies with regard to relatives for whom one is required to mourn according to Scriptural Law, he differs when the obligation to mourn is Rabbinic, e.g., for the son’s maternal brother. His rationale is that we generally do not institute a Rabbinic decree in support of another Rabbinic decree.
The Radbaz supports the Rambam’s position, explaining that it could be said that just as the following halachah speaks about mourning for the parents of one’s wife as a token of respect for her (although according to the Rambam, the obligation to mourn for her is Rabbinic); so, too, it can be said that one mourns for the relatives of one’s son as a token of respect for him. Alternatively, the Radbaz explains that in this instance, our Sages gave their decrees the strength of Scriptural Law to be sure that they would be heeded.
The Rambam’s ruling is quoted by Rav Yosef Karo in his Shulchan Aruch (Yoreh De’ah 374:6). The Ramah comments that in the present generation, this ruling is no longer observed. It was instituted only as a token of respect and it is customary for everyone to forgo such respect. Indeed, he writes that a person who fulfills this halachah by observing mourning rites is “one of the dolts.” [Significantly, in his Kessef Mishneh, Rav Yosef Karo quotes similar concepts (although using less severe wording)]. The Ramah continues, however, stating that it is customary in many communities for close relatives to observe a certain dimension of mourning.

See Halachah 3.

See Chapter 5, Halachah 18.

From a previous marriage.

This expression connotes a ruling for which the Rambam has no explicit source in the previous Rabbinic literature.

Note the Radbaz who asks: What is unique about the mitzvah of mourning? Any positive commandment supersedes a negative commandment. See also Halachah 15.

This represents the Rambam’s understanding of this verse and it is echoed by Targum Onkelos. As mentioned in the notes to Halachah 1, others translate the term differently.

It is not, however, considered a separate positive commandment from the commandment to mourn. Instead, they are two dimensions of the same commandment.
The Kessef Mishneh (in his gloss to Chapter 1, Halachah 1) explains the interrelation as follows: The Torah feared that since a priest is commanded to avoid contact with death, unless an explicit commandment was given to become impure, a priest would go to the other extreme and even refrain from mourning for his close relatives. Hence, to insure that he will mourn, he was commanded to become impure.

See Chapter 3, Halachah 11.

The Rambam’s rationale can be explained as follows: Since an Israelite and female member of the priestly family are not obligated to maintain distance from impurity, we do not fear they will refrain from mourning. Hence, there is no obligation for them to become impure.
The Ra’avad and Rabbenu Asher differ with the Rambam, maintaining that the female members of the priestly family are also obligated to become ritually impure while tending to the corpses of their deceased relatives. The Shulchan Aruch (Yoreh De’ah 373:3) follows their opinion.

Zevachim 100a states that there was a priest called Yosef whose wife died. He did not want to become impure by tending to her - for that would disqualify him from partaking of the Paschal sacrifice - and his priestly brethren compelled him to become impure.

As mentioned in the notes to Halachah 1, there are many who understand this to be a Scriptural command.

This term refers to the Hebrew meit mitzvah, literally “a corpse [that it is] a mitzvah [to bury].” See Chapter 3, Halachah 8. Just as a priest must become impure to bury an unattended corpse, he must become impure to bury his wife.

For one of the conditions of the marriage bond is that a husband becomes the sole heir of his wife’s estate (Hilchot Ishut 12:3).

According to the Rambam, the rationale for this ruling can be explained as follows: Since he does not inherit his wife’s estate until he marries her, he is not required to bury her. Instead, her heirs will perform that mitzvah.

Chapter 1, Halachot 6-11.

For some of these individuals, there are exegetical references which indicate that there is no license to become impure. In other instances, the concept is derived through deduction: Since the entire purpose of the license to become impure is to encourage the mitzvah of mourning, if there is no mitzvah to mourn, there is no license to become impure (Kessef Mishneh).

To summarize the point of this clause. A priest must attend the funeral of his close relatives; he may not visit their graves afterwards, however.
The Ramah (Yoreh De’ah 373:6) states that if there is a valid reason for a priest to disinter his relatives and rebury them, he may become impure while tending to their reburial until the second grave is covered.

E. g., a divorcee. Since he was obligated to divorce her, he is not required to mourn for her. Even if she bore him children, he may not become impure for her sake (Siftei Cohen 373:4).

Marrying a priest. Similarly, her first husband was also a priest. Otherwise, there would be no difficulty in either becoming impure for her sake.

See Hilchot Gerushin 10:7 which explains this situation in detail. The woman is not allowed to remain married to her first husband because she willingly engaged in relations with another man while married to him. She is not allowed to remain married to her second husband, because it was with him that she engaged in the relations that caused her to be forbidden to her first husband.

A challalah is a woman who engaged in relations that cause her to be forbidden to a priest or a woman born from such a union. We are speaking about an instance where the mother engaged in such relations after giving birth to this son (Siftei Cohen 373:6). Otherwise, the son is himself a challal and is permitted to become impure to all corpses (see Chapter 3, Halachah 11).

I.e., even if they are challalim who no longer have priestly privileges.

Even if she is later divorced (Radbaz; Kessef Mishneh).

And thus may have less physical signs of her virginity (see Hilchot Issurei Bi ‘ah 17:13).

For the word hoyita (Deuteronomy 24:2) is also interpreted as a reference to consecration (Kiddushin 5a).

And one does not inherit the estates of one’s maternal relatives, as stated in Hilchot Nachalot 1:6.

“To her” is seemingly an unnecessary phrase. Hence, our Sages understood it as communicating the following concept. Just as the priest is certain about the identity of “her,” his sister; so, too, he must be certain about the identity of all relatives (Malbim to Tarat Kohanim).
The Radbaz asks: Why would we think that the priest should become impure? Throughout the Torah, when there is a doubt concerning a Scriptural prohibition, we rule stringently. He explains that were it not for the verse, one might think that such a corpse is considered as unattended to. For because of the doubt involved, there will be no one with a clear-cut obligation to become impure.

I.e., two women, even two wives of priests, gave birth at the same time in the same place, and the babies became mixed up and neither was certain which baby was which. See Hilchot Issurei Bi'ah 20:4-5.

A woman was married and was widowed. Instead of waiting 90 days as required, she married immediately, became pregnant and gave birth within 9 months of her divorce from her first husband. We do not know if the child was conceived by her first husband (in which instance, he is his son with regard to all matters -) or by the second husband.

Neither the son to the father, nor the father to the son (Rabbi Akiva Eiger).

The son does not become impure for the sake of his father, since he is not certain if he is in fact his father. And if he were not to be his father, becoming impure for his sake would involve a transgression.
The commentaries raise a question: How is it possible for a priest to have such a question with regard to mourning for his wife’s first husband? The only way it is possible for her to have married her second husband is for the first husband to have died. Among the answers given is that the woman never actually married him and they conceived a child in wedlock.

E. g., a man threw a bill of divorce to his wife and there was a doubt whether the bill of divorce was closer to her (in which instance, the divorce is binding) or closer to him (in which instance, it is not). See Hilchot Gerushin 5:13. In these instances, the question is one of Scriptural Law.

I.e., a bill of divorce that is invalidated by Rabbinic decree. See ibid. 10:2.

In the latter instance, according to Scriptural Law, the divorce is valid, and certainly, the priest is forbidden to become impure for her sake. Even in the first instance, since a - question concerning a matter of Scriptural Law is involved, he is forbidden to become impure.

A limb severed from a living person conveys ritual impurity as stated in Hilchot Tumat Me’it 3:1.

The rationale for these laws is stated in the following halachah: A priest may only become impure for the sake of his relatives when their corpses are intact.
The Ra’avad - based on the ruling of Rabbenu Yitzchak Alfasi - differs with this conception. The Shulchan Aruch (Yoreh De’ah 373:9) quotes the Rambam’s view.

Or any other limb of his body [Radbaz; Shulchan Aruch (Yoreh De’ah 373:9)].

Even when the head is lying next to the body, if the corpse is not whole, a priest may not become impure for its sake (ibid.).

I.e., as reflected in the Rambam’s explanation, it is not as if this prohibition does not exist for the priest at this time. Instead, the intent is that the prohibition is ongoing. License is, however, granted to transgress it to bury one’s dead. See a parallel ruling in Hilchot Bi’at HaMikdash 4:15.

The commentaries debate the Rambam’s intent. His wording seems to imply even at the moment the priest is in contact with his relative’s corpse, he may not touch another corpse. There are, however, other opinions - and the Rambam’s words can also be interpreted in this manner - who maintain that at the moment he is touching his relative’s corpse, he may also touch other corpses. The stringency stated by the Rambam refers to the period before the burial is completed when he may not be in contact with his relative’s corpse.

According to the latter interpretation, the concern is when they return from the cemetery. According to the first interpretation, even on the way to the burial, there is reason for concern.
The Shulchan Aruch (Yoreh De’ah 373:7) quotes the Rambam’s words without clarifying his intent. The Tur and the Ramah follow the second view and the Bayit Chadash and the Siftei Cohen 373:12 mention the first perspective. See also the notes to Chapter 3, Halachah 4.