Kri'at Shema - Chapter One

We [are obligated to] recite the Shema twice daily, in the evening and in the morning - as [Deuteronomy 6:7] states: "...when you lie down and when you rise" - In Sefer HaMitzvot (Positive Commandment 10), the Rambam mentions the beginning of this verse, ודברת בם... (And you shall speak of them...) as the source for the mitzvah of Kri'at Shema.

Nevertheless, his statements in this halachah do not necessarily represent a change of mind. Here, the Rambam is not interested in the actual source for the mitzvah itself (which is the case in Sefer HaMitzvot), but in stating our obligation to recite the Shema twice daily, once at night and once in the daytime. This is derived from the end of the verse, as mentioned by the Rambam.

in the evening and in the morning - The obligation to recite the Shema at night is mentioned first both in the Mishnah,Berachot 1:1 and here in the Mishneh Torah, following the pattern mentioned in the verse quoted above: "...when you lie down and when you rise."

Berachot 3a understands this order as parallel to the creation of the world itself which began: ויהי ערב ויהי בקר (And then there was night and there was day..., Genesis 1:5). (See also the Rambam's commentary on the Mishnah, Berachot 1:1.)

i.e., when people are accustomed to sleep - this being the night - and when people are accustomed to rise - this being daytime. - The Mishnah (Berachot 10b) records a disagreement between the school of Shammai and the school of Hillel regarding the laws derived from the verse: "... and when you lie down and when you rise."

Both agree that the Shema is recited twice daily, once at night and once in the morning. However, based on the above verse, Beit Shammai obligates one to recline while reciting Kri'at Shema at night, and to stand while reciting it in the morning. Beit Hillel holds that the verse simply establishes the general times at which the Shema is recited, as stated by the Rambam in this halachah; i.e., at the time that people sleep and at the time that they are accustomed to wake up.

And what is it that one recites? - There are various opinions as to what constitutes the positive commandment of Kri'at Shema. Sefer HaChinuch (Commandment 419) states clearly that the Torah obligates us to read only the first verse of the Shema - i.e., Shema Yisrael. The reading of the rest of the three sections was instituted by the Sages.

Rabbenu Yonah understands that the whole first section constitutes the Torah obligation. (See Beit Yosef, Orach Chayim 63 at the end.) There is also an opinion that the obligation to recite the first two sections originates in the Torah. (See Shulchan Aruch HaRav, Orach Chayim 58.) However, in practice, everyone ultimately agrees that one must recite all three sections mentioned by the Rambam in this halachah (Berachot 13a).

These three sections: "Hear O Israel..." (Deuteronomy 6:4-9), "And if you will listen..." (Deuteronomy 11:13-21) and "And God said..." (Numbers 15:37-41). - For, as explained, each of these paragraphs contains fundamental concepts central to the Jewish faith.

Note Sefer HaChinuch (Commandment 420) who quotes the Rambam, not to explain the order of Kri'at Shema, but rather to clarify why the Sages included these three sections in the Shema.

we begin with the section of "Hear O Israel..." - Berachot 13a, 14b, offers two different explanations regarding the order of Kri'at Shema. The Rambam, however, does not quote either explicitly, but rather seems to suggest his own reason.

The Kessef Mishneh holds that the Rambam's explanation of the order of the first two sections, "Hear O Israel" and "And if you will listen," is in fact consistent with the Mishnah in Berachot 13a. Regarding the last section, the Rambam desired to supply us with both the reason for its inclusion and its placement after the second section (even though the third section precedes it in the Torah itself).

since it contains [the concept of] the unity of God - The statement "God is our Lord, God is one" implies not only that there is only one God, but all creation is one with Him. See Shulchan Aruch, Orach Chayim 61:6.

[the commandment of] loving Him - "And you shall love God, your Lord, with all your heart, with all your soul and with all your strength" (Deuteronomy 6:5).

the study of Torah - "... and you shall teach your children and speak of them" (Deuteronomy 6:7).

It must be noted that in Hilchot Talmud Torah, the Rambam quotes Deuteronomy 11:19 (a verse in the second section of the Shema), as the source for the mitzvah of Torah study.

it being a fundamental principle upon which everything is based - This refers to the concept of the unity of God. (See Hilchot Yesodei HaTorah 1:6.)

After it [we read] "And if you will listen...," since it contains the imperative to fulfill the rest of the commandments - "And if you will listen to all my commandments..." (Deuteronomy 11:13). This section also contains the commandment of loving God (verse 13) and the study of Torah (verse 19). It is, however, the mention of "all the commandments" which distinguishes this section as separate and unique from the first section.

and finally the portion of tzitzit, since it also contains the imperative of remembering all the commandments - "And you shall see them (tzitzit - the fringes on the corners of four-cornered garments) and remember all the commandments of God and do them" (Numbers 15:39).

Rashi, in his commentary on the above verse, explains how tzitzit serve as a reminder of all the Torah's commandments. The numerical value of the Hebrew word ציצית is 600 (צ = 90 י = 10 צ = 90 י = 10 ת = 400) There are also eight strings and five knots. Therefore, by looking at the tzitzit, one is reminded of the 613 divine commandments.

The commandment of tzitzit is not obligatory at night - Numbers 15:39 states: "And you shall see them..." - implying that tzitzit must only be worn when they can be seen, i.e., daytime. Accordingly, there is no obligation to wear tzitzit at night. See Hilchot Tzitzit 3:7-8.

Nevertheless, we recite [the section describing] it at night because it mentions the exodus from Egypt - "I am God, your Lord, who took you out of the land of Egypt to be your Lord, I am God, your Lord" (Numbers 15:41).

The Kessef Mishneh explains that the mention of the exodus can itself be understood as the reason for the inclusion of this section in Kri'at Shema. The Rambam, however, mentions tzitzit as the basis for the presence of this section in Kri'at Shema (see Halachah 2), since it is the tzitzit that cause us to remember all the commandments.

We are commanded to mention the exodus from Egypt both during the day and at night - See Berachot 12b.

It is interesting to note that in Sefer HaMitzvot, the Rambam does not count the mentioning of the exodus from Egypt as one of the 613 commandments in the Torah, nor does he mention it elsewhere in the Mishneh Torah.

The Rambam does, however, count the commandment of the telling of the story of the exodus on the fifteenth of Nisan - i.e., Passover night - as one of the mitzvot. See Sefer HaMitzvot (Positive Commandment 157), Sefer HaChinuch (Mitzvah 21), and Hilchot Chametz U'Matzah, Chapters 7 and 8.

According to some opinions, one can differentiate between the two obligations as follows: A person can fulfill his daily obligation with simply a thought about the exodus, whereas on Pesach night the mitzvah can be performed only through the verbal description of the redemption from Egypt. (See Sha'agat Aryeh, 13.)

This would explain the omission of this commandment from Sefer HaMitzvot. A commandment that can be fulfilled with a thought alone and not an explicit statement or action is not "worthy" of inclusion in the list of 613 commandments of the Torah. (See the Rambam's explanation of the commandment to remember Amalek: Positive Commandment 189).

The Aruch HaShulchan, however, disagrees with this opinion. In Orach Chayim 67, he states that even the daily obligation requires an explicit statement. Nevertheless, he explains that it was not chosen as one of the 613 commandments because the obligation to remember the exodus twice daily is not stated in the form of a command in the Torah to "Remember," but rather, as a reason for another mitzvah (the mitzvah of matzah): "In order that you shall remember..." (Deuteronomy 16:3).

all the days of your life - The word "all" includes even the nighttime.

The Zohar (Parshat Vayakhel 216b) explains the mystical significance of mentioning the exodus from Egypt after proclaiming the unity of God.

The reading of these three sections in this order constitutes the recitation of the Shema. - The Jerusalem Talmud (Berachot 1:5) mentions that the sections of Kri'at Shema also contain a reference to each of the 10 utterances of the revelation at Mount Sinai (Exodus 20:1-14), thus representing a complete statement of Jewish spirituality and values.

When reciting the Shema, after completing the first verse, one says quietly: "Blessed be the name of the glory of His Kingdom forever." - This phrase is recited quietly because it is not part of the section of the Shema as it appears in the Torah, but rather was recited by Jacob in Egypt, as explained later in this halachah.

It is, however, pronounced loudly on Yom Kippur. Pirkei D'rabbi Eliezer explains that the angels praise God with this verse. On Yom Kippur, we are as pure as angels and thus, emulate their practice (Hagahot Maimoniot).

It is preferable to separate clearly between the end of "Blessed be the name" - i.e., the words לעולם ועד - forever, and the beginning of the next section, ואהבת (And you shall love...) (Tur, Orach Chayim 61).

He then continues to read the first section. Why do we read it in this fashion? - i.e., Why do we include this verse of "Blessed be the name...," since it is not part of the section of the Torah beginning with "Shema Yisrael..."

It is our tradition that when the patriarch, Jacob, gathered all his sons together in Egypt close to his death - See Genesis, Chapter 49.

he commanded and urged them regarding the Unity of God and the path of God upon which Abraham and Isaac, his father, had tread. - This narrative can be found in Pesachim 56a.

He asked them: "My sons, perhaps there are dregs among you, one who does not stand with me in the Unity of God?" - What would cause Jacob to have such a doubt regarding his children? One of the greatest merits of Jacob is that he - unlike Avraham, who fathered Yishmael, and Yitzchak, who had Esau as a son - had only righteous children.

Pesachim (ibid.) explains that Jacob desired to reveal the secret of the end of days to his children, but that this knowledge suddenly left him. He was worried that perhaps his sudden lack of understanding was due to the imperfect state of his children and therefore, felt compelled to ask them about their faith in the One God.

The Rambam omits all these particulars, since they are not relevant to the matter at hand - namely, the source of the custom of saying "Blessed be the name..." after "Shema Yisrael..."

This is comparable to the manner in which Moses, our teacher, said to us: "Lest there be among you a man or woman [whose heart turns this day from God...]" - The Rambam adds this in order to teach us the nature of Jacob's doubts. He was not casting aspersions on the behavior of his sons, since he knew that their deeds were righteous. He was, however, worried that perhaps one of them had a mistaken understanding regarding the unity of God. This is in line with the verse the Rambam quotes. Moses is not chastising the Jewish people for their actions, but rather warning them of the possibility that there might be someone with a lack of faith that could lead to blasphemy later (Kessef Mishneh).

They all answered and said: "Listen, Israel, - Jacob is also called by that name (Genesis 32:29).

God is our Lord, God is One," i.e., listen to us, Israel, our father, God is our Lord, God is One.

The wise elder responded: - Praising God for the fortune of having righteous children;

"Blessed be the Name of the Glory of His Kingdom forever." Therefore, the Jews are accustomed to utter the praise that Israel, the wise elder, uttered after this verse.

Commentary, Halachah 5

Blessings are recited before and after Kri'at Shema. - See the Mishnah, Berachot 11a.

In the day, one recites two blessings before it and one after it. At night, one recites two blessings before and two blessings after it. - There are a total of seven blessings associated with the reading of the Shema, three in the day and four at night. The Jerusalem Talmud (Berachot 1:5) bases this on the verse "Seven (times) in the day will I praise you" (Psalms 119:164).

The Tanya, Chapter 49, discusses the reasons for these blessings at length, noting that, on the surface, they are not related to the Shema at all. That text explains that the basic intent of Kri'at Shema is to attain the love for God as described in the verse, "And you shall love God, your Lord, with all your heart, with all your soul and with all your strength."

To reach such a level, one must first contemplate the greatness of God. Accordingly, in the first blessing, we outline the praises of God uttered by the angels, who are of supreme intelligence and spiritual wisdom. These lofty creatures proclaim God's greatness and abnegate themselves completely to Him, stating that He transcends even their ability to understand.

Then, in the second blessing, we describe God's great love for the Jewish people, as manifested by His giving us His Torah and choosing us as His people.

Having contemplated such ideas, we are prepared to reciprocate God's love for us by proclaiming our love for Him. We recognize His infinite Greatness and Unity, see His Providence in the events of our life, and internalize our intellectual understanding into an emotional outpouring for our Creator.

The first blessing preceding [the Shema] in the day [begins: "Blessed are You, God...], the One who forms the light and creates darkness etc." - Berachot 13b mentions that the Sages required the mention of night during the day to contradict clearly the misunderstanding of the non-believers that He who created light did not create darkness.

The second blessing [begins with]: "With everlasting love, You have loved us..." - The opening phrase of this blessing is the subject of a disagreement between the Sages (Berachot 11b). Rav Yehudah says in the name of Shmuel that the blessing should begin with אהבה רבה (Great love). The Sages, based on the verse in Jeremiah 31:2, believe that it should begin with אהבת עולם (Everlasting love). The Rambam follows the latter opinion.

The Tur (Orach Chayim 60) mentions that the Talmud instituted the custom of saying אהבה רבה in the morning and אהבת עולם at night in order to meet the requirements of both positions. Tosafot in Berachot 11b and the Rosh are also in favor of such a solution. The Shulchan Aruch, Orach Chayim 60a rules in accordance with the Rambam's position.

Ashkenazim are accustomed to recite the blessings as preferred by the Rosh and the Tur. (See the Ramah on Shulchan Aruch, Orach Chayim 60a.) Sephardim and those who pray according to the Nusach Sephard, the prayer text generally used by Chassidim today, say אהבת עולם twice daily, both in the day and at night.

[The Shema] is followed by [the section beginning] "True and certain..." - affirming the truth of the statements mentioned in the Shema.

At night, the first blessing preceding [the Shema begins: "Blessed are You, God...], the One who brings the evening,..." and the second [begins with] "With everlasting love, You have loved Your people Israel." The first blessing after [the Shema] is [the section begining] "True and faithful..." - These blessings parallel the content of the three blessings recited in the morning.

and the second [begins] "Lay us down..." - in preparation for going to sleep.

To understand this halachah fully, a short introduction to the rules contained within it is necessary. The Mishnah (Berachot 11a) and the Tosefta (Berachot 1:7) discuss the concepts of the beginning (p'tichah, פתיחה) and conclusion (chatimah, חתימה) of blessings.

The p'tichah of a blessing follows the formula of "Blessed are You O God, our Lord, King of the Universe..." The chatimah of a blessing is "Blessed are You, O God..."

Some blessings have both a p'tichah and a chatimah (e.g., the first blessings before Kri'at Shema both in the day and at night and the blessing made at Kiddush of Friday night), while others have only a p'tichah (e.g. blessings made before eating food or performing a commandment) or a chatimah (e.g., the rest of the blessings of Kri'at Shema and the majority of the blessings of the silent Amidah prayer).

The first blessing preceding it, both in the day and at night, begins "Blessed [are You, God our Lord...]" and concludes "Blessed [are You, God...]" - The first blessing in a series of blessings generally possesses a p'tichah, as well as a chatimah. Other examples of this are the first blessing in the silent Amidah prayer and the blessing with which we begin grace after meals.

The rest of the blessings all conclude with "Blessed [are]...", but do not begin "Blessed [are]..." - A blessing which immediately follows another as part of a series of blessings is not introduced with a p'tichah (Berachot 46a). The paragraphs of "True and certain" and "True and faithful" are also considered as blessings that follow another blessing, even though the Kri'at Shema itself would seem to constitute an interruption. Therefore, these blessings need not begin with a p'tichah, but simply conclude with the standard chatimah: Blessed are You, God (Rashi, Berachot 36a).
[

The Rambam discusses only the concepts of p'tichah and chatimah and omits the second category of blessings mentioned in the Mishnah and Tosefta (i.e., long and short blessings). This seems to indicate that he equated a long blessing with that which has a p'tichah and a chatimah, and a short blessing with one that has only a chatimah (Kessef Mishneh). In fact, in his commentary on the Mishnah (Berachot 11a), the Rambam writes that even a long blessing has a p'tichah and chatimah, and a short one has only one of the above.

In contrast, Rashi (Berachot 11a) holds that the distinction between long and short blessings is a matter of length only, irrespective of p'tichot and chatimot. He defines the blessing of אמת ואמונה - "True and faithful" - (the first blessing after Kri'at Shema at night) as a long blessing, and "Lay us down" (the last blessing after Kri'at Shema at night) to be a short blessing, even though they both have only a chatimah and no p'tichah.]

These blessings and all the rest of the blessings familiar to the Jewish people were instituted by Ezra, the scribe, and his court - This is a general statement. In particular, there are some blessings that were not established by Ezra, but rather by the Sages of the Mishnah. See Hilchot Tefillah 2:1 and Hilchot Berachot 2:1.

One may not detract from them or add to them.

In every instance that they decreed to conclude with "Blessed..." - e.g., all the blessings of Kri'at Shema, the silent Amidah prayer and grace after meals. (See the introduction to this halachah in order to understand the following laws fully.)

One may not omit it.

Where they decreed not to conclude [with "Blessed..."] - e.g., blessings for food and preceding the performance of commandments.

one may not conclude with it.

Where they decreed not to begin... - e.g., all blessings that follow another in a series of blessings, such as the silent Amidah or the blessings before Kri'at Shema.

One may not begin with it.

Where they decreed to begin [with "Blessed..."] - e.g., the first blessings of Kri'at Shema, the silent Amidah prayer and grace after meals.

one may not omit it.

The general principle is that anyone who deviates from the set form of blessings established by the Sages is mistaken and must recite the blessing again in its proper form - This decision is based on the Mishnah (Berachot 11a).

In Hilchot Berachot (1:5-6), the Rambam writes that a person who mentions the central ideas contained in the p'tichah - i.e., the name of God and His sovereignty - even were he to deviate from the set form of the blessing, would fulfill his obligation.

We must understand the present halachah in this context. Only when one deviates from the p'tichah or chatimah of a blessing does the Rambam require the recitation of another blessing. However, a person who maintains the nature of the p'tichah and chatimah, but changes the wording of the rest of the blessing, fulfills his obligation as long as the basic intent of the blessing remains.

Anyone who does not say [the paragraph of] "True and certain..." in the morning prayer or [the paragraph of] "True and faithful..." in the evening prayer - Berachot 12a derives this from Psalms 92:3: "To relate Your lovingkindness in the morning and Your faithfulness at night." Rashi explains that ויציב אמת, "True and certain" (which is recited after Kri'at Shema in the morning) is necessary, since it tells of God's infinite lovingkindness in taking our forefathers out of Egypt and splitting the Red Sea.

אמת ואמונה (True and faithful) (which is recited at night) chronicles our hopes and beliefs regarding our future, that God will fulfill His promise to redeem us from the exile and restore us to a vibrant life of freedom. The Tur (Orach Chayim 66) explains that אמת ואמונה (True and faithful) could also refer to our faith that God will return our soul, which we put in His trust every night, to us.

does not fulfill his obligation - Rav Hai Gaon holds that the blessings of Kri'at Shema are an integral and necessary part of the fulfillment of the commandment. Therefore, he explains Berachot 12a as saying that one who does not say Emet v'yatziv has not fulfilled his obligation of Kri'at Shema and must therefore recite it again. The Rambam appears to accept this opinion.

However, the vast majority of the Rishonim are of the opinion that a person can fulfill his obligation to recite the Shema even if he does not recite the blessings. The above passage, therefore, is to be understood as teaching that one has not performed the mitzvah in its proper fashion if he omits the blessings.

Both the Tur and the Shulchan Aruch (Orach Chayim 66:10) reflect this understanding. They add the word "properly" at the end of this halachah: "One who does not say Emet v'yatziv, etc., does not fulfill his obligation properly. He need not, however, recite the Shema again."

One who recites the second blessing - e.g., Ahavat Olam

before the first - e.g., yotzer or,

Even in such an instance, the second blessing should be recited without a p'tichah, since it usually follows another blessing (Kessef Mishneh). See also Magen Avraham on Orach Chayim 60:3.

whether in the day or at night, or whether the transposed blessings are recited before or after Kri'at Shema, - i.e., even if he recites all the blessings after reciting the Shema.

fulfills his obligation, since there is no absolute order to the blessings - "And what does it mean that blessings are not an integral and necessary requirement? This refers to the order of the blessings" (Berachot 12a).

A person who begins with "...the One who forms the light..." - i.e., "Blessed are You, God, our Lord, King of the universe, who forms the light and creates the darkness (חושך וצר אור ובורא), this being the proper p'tichah for the first blessing before Kri'at Shema in the morning.

and concludes with "...the One who brings the evenings" - i.e., Blessed are You O God, who brings the evenings (המעריב ערבים), this being the proper chatimah for the first blessing at night.

in the morning prayer does not fulfill his obligation. - As explained later in this halachah, all the blessings are ultimately defined by their chatimah. In this case, the chatimah is that of the evening blessings and is therefore inappropriate here.

Were he to begin with "...the One who brings the evenings" - i.e., "Blessed are You O God, our Lord, King of the universe, who, through His word, makes evenings fall (אשר בדברו מעריב ערבים)," this being the proper p'tichah for the first blessing at night.

and conclude with "...the One who forms the light" - the conclusion of which is "Blessed are You O God, who forms the lights (יוצר המאורות)," this being the proper chatimah for the first blessing in the morning

he would fulfill his obligation - since the chatimah is proper.

Were he to begin with "...the One who brings the evenings" - i.e., "Blessed are You O God, our Lord, King of the Universe, who through His word, makes evenings fall (אשר בדברו מעריב ערבים) ," this being the p'tichah for the first blessing at night

...and conclude with "...the One who forms the light" - i.e., "Blessed are You O God, the One who forms the lights (יוצר המאורות)," this being the proper chatimah for the first blessing in the day.

in the evening, he would not fulfill his obligtation. - since the chatimah is inappropriate.

If he begins with "...the One who forms light" - i.e., "Blessed are You O God, our Lord, King of the Universe, who forms light and creates darkness (יוצר אור ובורא חושך)," this being the p'tichah for the first blessing in the day.

and concludes with "...the One who brings the evenings" - i.e., "Blessed are You O God, the One who brings the evenings המעריב ערבים," this being the chatimah for the first blessing at night.

he fulfills his obligation since all blessings are defined by their conclusions - i.e., by their chatimot. This entire halachah is based on Berachot 12a. That passage discusses whether the p'tichah or chatimah is the ultimate defining feature of a blessing and reaches this conclusion.

The Shulchan Aruch, Orach Chayim 59:2 explains that though the chatimah is the primary determining factor, the text of the blessing must also be appropriate.

Thus, were one to recite the whole paragraph of "... The One who brings the evenings" and then say "Blessed are You O God, who forms the lights," he would not fulfill his obligation regarding the first blessing of Kri'at Shema in the morning, even though he recited the proper chatimah.

When is the [proper] time for the recitation of Shema at night? The commandment [starts] from the time of the appearance of the stars... - The Mishnah (Berachot 2a) states that the time for the recitation of the Shema begins at the hour when a priest who has become ritually impure may immerse in a mikveh and resume eating terumah. The Talmud explains that this is the time when the stars appear.

Tosafot (Berachot 2a) holds that the Shema may be recited earlier, during the last hour before sunset. This is based on the understanding that Rabbi Yehudah, who disagrees with the majority opinion regarding the proper time for the afternoon prayer, also disagrees about the proper time for the evening prayer and Kri'at Shema contained therein. (See Tur, Orach Chayim 235.) This will be discussed at length in Hilchot Tefilah 3:6.

There are several different positions regarding the precise definition of צאת הכוכבים (the appearance of the stars). It generally refers to the appearance of three medium-sized stars. The Shulchan Aruch, Orach Chayim 235:1 requires the sighting of three small stars before reciting Kri'at Shema at night. The Magen Avraham explains that the basic halachah is indeed that three medium sized stars constitute the time of צאת הכוכבים, but that the Shulchan Aruch obligated one to wait for smaller stars in order to diminish the possibility of error regarding the recitation of Kri'at Shema at night.

There are three basic positions regarding the actual time of צאת הכוכבים (the appearance of the stars). Shabbat 34b determines that it refers to the time that it takes one to walk 3/4 of a mil after sunset.

The other two positions are found in Pesachim 94a: one defines צאת הכוכבים as the amount of time needed to walk four mil after sunset, and the other, as the time necessary to walk five mil.

There are two different methods of determining the time it takes to walk a mil. The Rambam, Commentary to the mishnah, Pesachim 3:2, maintains that it takes 24 minutes to walk a mil. However, the most widely held opinion - and the opinion accepted regarding halachah l'ma'aseh - is that the measure of time is 18 minutes.

Therefore, according to Shabbat 34b, the appearance of the stars is 13 1/2 (3/4 x 18) minutes after sunset. Both the Vilna Gaon and the Shulchan Aruch HaRav maintain that צאת הכוכבים is determined in this fashion. Thus, the proper local time may be calculated by extrapolation based on the amount of light visible 13 1/2 minutes after sunset in Eretz Yisrael on the day of the Equinox. Generally, people wait up to 36 minutes after sunset in order to be certain.

According to Pesachim 94a, the appearance of the stars will be either 72 (4 x 18) minutes or 90 (5 x 18) minutes after sunset. Rabbenu Tam strongly suggests adhering to the position that צאת הכוכבים takes place 72 minutes after sunset. Though some authorities support the 90-minute position, Rabbi Moshe Feinstein (Iggerot Moshe, Orach Chayim, Vol. 1, Siman 24), mentions only the position of the Vilna Gaon and the Shulchan Aruch HaRav, on the one hand, and Rabbenu Tam on the other.

[and continues] until midnight - There are three positions recorded in the Mishnah in Berachot 2a regarding the time until which one may recite the Shema at night.

Rabbi Eliezer says until the end of the first of the three watches of the Temple - i.e., one third of the night, which is until approximately 9:30 pm. The Sages say until midnight, and Rabban Gamliel says until dawn. The Mishnah then explains that the Sages' opinion is, in effect, that one may recite the Shema until dawn, but that they mentioned midnight as a preferred time in order to distance people from transgression. This is the source of this halachah in the Rambam.

The Rosh and the Tur (Orach Chayim 235) hold that the halachah follows Rabban Gamliel's position, and that a priori (לכתחילה), a person may read the Shema at night until dawn. The Rambam sees the Sages' position as halachically valid, and therefore one may rely on Rabban Gamliel only after the fact (בדיעבד). The Shulchan Aruch, Orach Chayim 235:3 quotes the Rambam's position. (See also Mishnah Berurah 235:34-35.)

A person who transgresses and delays - the Rabbinic decree that the Shema should be read before midnight.

fulfills his obligation if he recites [the Shema] before dawn. - In his commentary on the Mishnah (Berachot 1:1), the Rambam defines dawn (עלות השחר) as the light that radiates from the east before sunrise.

There are three major positions regarding this time. All are based on Pesachim 94a which defines the time from dawn until sunrise as that in which a person can walk either 4 mil (according to one opinion) or 5 mil (according to the other).

As mentioned above, there are two opinions regarding the measure of time it takes to walk a mil: 18 minutes or 24 minutes. Thus, Rav Shneur Zalman of Liadi defines dawn as 120 (5 x 24) minutes before sunrise. The most widely held view is that it is 90 (5 x 18) minutes before sunrise, while the Beit Yosef holds that dawn is 72 (4 x 18) minutes before sunrise. This is the opinion of the Rambam, as stated in his commentary on the Mishnah (Berachot 1:1.)

[The Sages established the limit] of midnight only in order to distance us from negligent wrongdoing. - Berachot 1:1 lists other instances where the Sages established similar guidelines, e.g., partaking of sacrificial meat, burning sacrificial limbs.

One who reads the Shema [of the night] after dawn - as explained above, dawn is generally defined as the end of the night.

[but] before sunrise - the last possible time that could be defined as night

does not fulfill his obligation unless he was unavoidably detained - e.g., drunk or sick, or in a similar situation. -

Rabbi Shimon bar Yochai said in the name of Rabbi Akiva: "Sometimes a person can recite the Shema twice in the day, once before sunrise and once after sunrise, and fulfill his obligation - once for the day and once for the night."
Rabbi Yehoshua ben Levi says: "The law follows [the statement of] Rabbi Shimon in the name of Rabbi Akiva." Rav Zeira says: "This is so, provided that he does not say [the paragraph of] "Lay us down" (Berachot 8b-9a).

The Talmud explains that Rabbi Shimon's statement only applies when a person is unavoidably detained. The evening Shema must be recited "when you lie down." The Torah left the definition of that term to the Rabbis. The latter maintained that a person who intentionally delays the recitation of the Shema cannot recite it after dawn. However, they were more lenient in regard to a person who was unavoidably detained and gave him until sunrise.

A person who was so detained and reads [the Shema] at this time does not recite [the blessing of] "Lay us down." - for this is not a time when a person lays himself down to sleep. Nevertheless, one does recite the other blessings related to Kri'at Shema at night (two before and one after it).

When is the proper time [for the recitation of the Shema] during the day? The commandment is that one should start to read before sunrise - The Mishnah, (Berachot 9b) records a disagreement regarding the time of Kri'at Shema in the morning.

An anonymous position sees the earliest possible time as when one can distinguish between techelet (blue-green) and white. Rabbi Eliezer says: Between green and blue-green - i.e., later - and that the time lasts until sunrise. Rabbi Yehoshua says that one may recite the Shema "until three hours."

The Talmud then adds various other opinions and quotes Abaye as saying that the Shema should be recited כותיקין - i.e., one should finish reciting the Shema as the sun rises, in order to start the silent Amidah with the sunrise.

The Rambam clearly prefers this position and establishes 6 minutes as a reasonable amount of time to recite the Shema and the blessing after it, in order to start the Amidah at the proper time. The Magen Avraham (Orach Chaim 58:1) explains that all opinions agree that the commandment to recite Shema in the morning begins at dawn. The only disagreement revolves around the optimum time to recite Kri'at Shema. The Vilna Gaon differs and explains that the Rambam holds that Abaye's position states the actual time of the beginning of the commandment itself and that it may be recited earlier only in extraordinary circumstances.

in order to conclude and recite the last blessing with the sunrise - i.e., אמת ויציב (True and certain...), which concludes: Blessed are You O God, who redeemed Israel.

This measure [of time] is one-tenth of an hour before the sun rises - This is based on the verse in Psalms 72:5, "May they fear You with the sun" - i.e., may they show their fear for You with the Amidah as the sun rises (Berachot 9b). The Talmud promises that anyone who recites the Shema and the Amidah at this time is guaranteed a place in the World to Come.

A person who delays and reads the Shema after the sun rises fulfills his obligation, for the proper time is until the end of the third hour of the day - These do not refer to normal 60-minute hours, but are based on a different calculation. These hours are שעות זמניות - "seasonal hours," i.e., 1/12 of the duration of the daylight hours. The day and night are each divided into 12 equal parts, and each "hour" is 1/12 of that time.

For example, if there were 18 hours of daylight and 6 hours of darkness on a given day, each "hour" of the day would be 18/12 hours (or 90 minutes), and each "hour" of the night would be 6/12 hour (or 30 minutes).

There is a disagreement regarding how to calculate the durations of daylight and nighttime. The Magen Avraham holds that daylight is divided into 12 equal parts from dawn until the appearance of the stars. The Shulchan Aruch HaRav and the Vilna Gaon hold that daylight is determined from sunrise to sunset.

Therefore, the end of the third hour according to the Magen Avraham is earlier than that of the Shulchan Aruch HaRav and the Vilna Gaon, and even though each "hour" is longer, it is calculated from dawn, which is at least 72 minutes before sunrise. (See the commentary on Halachah 9.)

for one who transgresses and delays. - The use of the term "transgresses" (מי שעבר) is most striking in this context. We must say that the Rambam understands Rabbi Yehoshua's position as secondary and that, at the outset, one should recite the Shema 6 minutes before sunrise. Indeed, in his responsa, he writes that it it is preferable to read the Shema without a minyan before sunrise, than to wait until after sunrise to recite it together with a minyan.

The majority of Rishonim (see Rabbenu Asher on Berachot 9b and Beit Yosef, Orach Chayim 58) disagree with the Rambam and understand that although reciting Kriat Shema just prior to sunrise is the most desirable method of fulfilling one's obligation (מצוה מן המובחר), the actual commandment is from before sunrise (i.e., the time at which one can recognize his friend 6 feet away) to the end of the third hour. (See Shulchan Aruch, Orach Chayim 58:1 and the definition there regarding the proper time for the commandment.)

One who is overhasty and recites the Shema of the morning prayers after dawn, even though he finishes before sunrise, fulfills his obligation. - This implies that this is not most desirable. Rather, prefarably, the Shema should be read immediately before sunrise, and any other time is clearly considered second best.

In extraordinary circumstances - e.g., one who rises early in order to travel - and a delay would cause him aggravation and prevent him from concentrating on his prayers

Rabbenu Manoach cites other examples when leniency is granted, among them a day when there is a burial or a bris, or Hoshanah Rabbah, when the prayer service is extended.

one may recite it at the outset from dawn. - i.e., generally, reciting the Shema at dawn is undesirable, but in this instance, the Sages considered this as the most preferable option.

One who recited [the Shema] after [the end of] the third hour, even if he was unavoidably detained, does not fulfill his obligation to recite the Shema at its proper time. - The morning Shema must be recited "when you rise" (Deuteronomy 6:7). The latest time of rising is understood as the end of the third hour, the time that royalty rises (Berachot 9b). Even if a particular individual rises afterwards, he is considered as an exception and no leniency is granted.

The Kessef Mishneh questions why Kri'at Shema may be read in the daytime until only the end of the third hour.
Just as the obligation to recite the Shema at night lasts the entire night because the entire night is a time of lying down, so too, the Shema of the daytime should be recited all day, since the entire day is a time of being up.

The Taz (58:6) distinguishes between the nighttime, all of which is indeed a time of lying down, and the daytime. There are many acts that one does during the day - e.g., walking, sitting and eating - while rising is generally done at the beginning of the day.

He can be compared to one who studies Torah. - The Shema is also a passage in Torah. Furthermore, by reading the Shema, one accepts the yoke of heaven. Nevertheless, the reward received by a person who reads the Shema at the proper time is greater (Berachot 10b).

When a person reads the Shema at such a time...

He should recite the blessings - mentioned in Halachot 5-7.

preceding it and after it all day - Rabbenu Asher differs and limits the time when the blessings can be recited. He is unsure whether the limit is midday or until the end of the fourth hour, that being the end of the time for the morning prayers. In conclusion, he quotes Rav Hai Gaon who states that one may recite the blessings only until the end of the fourth hour - i.e., one third of the day. Rabbenu Chanan'el is also of this opinion.

Rabbenu Manoach agrees with the Rambam and allows one to recite the blessings during the entire day. The Shulchan Aruch, Orach Chayim 58:6 follows the position of Rav Hai Gaon.

even if he delays and recited it after [the end of] the third hour. - Even if one delays the Shema's recitation intentionally, he may recite the blessings.