Gemara

(R. Zeira): If a Minchah could have been mixed, mixing is not Me'akev. If it could not have been mixed, (e.g. it is too big), mixing is Me'akev (i.e. it is Pasul).

Berachos 13a (Beraisa - Rebbi): Keri'as Shma must be recited like it is written (in Hebrew);

Chachamim say, it may be recited in any language.

Chachamim learn from "Shma" (hear), in any language you understand. Rebbi expounds "Shma" to obligate saying the words audibly to his own ears. Chachamim hold that one is Yotzei even if it was not audible to his ears.

15a (Mishnah): If one said Keri'as Shma inaudibly (to his own ears), he was Yotzei;

R. Yosi says, he was not Yotzei.

(Beraisa #1): One may not say Birkas ha'Mazon in his heart. If he did, he was Yotzei.

(Beraisa #2): A Cheresh (in this Halachah, this refers to a deaf person who can speak) may take Terumah l'Chatchilah (even though he cannot hear his own Berachah).

(Beraisa #3): A Cheresh child cannot recite Megilas Esther (and be Motzi adults);

R. Yehudah permits a Katan.

Resolution #1: Beraisa #2 is like R. Yehudah. He permits l'Chatchilah. Beraisos #1 and #3 are like R. Yehudah citing his Rebbi.

(Beraisa - R. Yehudah citing R. Elazar (ben Azaryah)): One must say Shma audibly to his own ears -- "Shma Yisrael..."

R. Meir: It says "Al Levavecha" -- intent suffices!

Resolution #2: R. Yehudah could agree with R. Elazar. Beraisa #2 is like R. Meir.

(Rav Chisda): The Halachah follows R. Elazar, and it follows R. Yehudah (in our Mishnah).

Had he taught only that the Halachah follows R. Yehudah, one might have thought that even l'Chatchilah he need not hear himself. Had he taught only that the Halachah follows R. Elazar, one might have thought that he must hear himself, and a Cheresh cannot be Yotzei.

(Rav Yosef): They argue about Keri'as Shma, for it says "Haskes u'Shma Yisrael" (you must hear yourself). For other Mitzvos, all agree that he was Yotzei.

(Rav Yoshiyah): The Halachah follows the lenient opinion.

20b (Mishnah): A Ba'al Keri (one who had a seminal emission; he may not say Divrei Torah or pray until he immerses) thinks in his heart the Berachos before and after Keri'as Shma, but he does not say them. He blesses after eating, but only thinks in his mind the Berachah Rishonah.

R. Yehudah says, he blesses before and after.

(Ravina): Our Mishnah teaches that Hirhur (thought) is k'Dibur (like speaking). If not, there would be no reason to have Hirhur!

Question: If Hirhur k'Dibur, it should be permitted to say the words!

Answer: This is like we find at Sinai. (Bnei Yisrael became Tahor in order to hear the Torah. However, even a Ba'al Keri may think Torah.)

(Rav Chisda): Hirhur is not k'Dibur. If it were k'Dibur, he should say the words!

Question: If so, why must he think Shma?

Answer (R. Elazar): He should not be idle while everyone else is saying Shma.

(Rav Ada bar Ahavah): (He could think about any Divrei Torah, but) it is proper to engage in the same matter as the Tzibur.

Shabbos 150b (R. Yochanan): R. Yehoshua ben Korchah expounds "v'Daber Davar" - Dibur (about Melachah) is forbidden on Shabbos, but Hirhur is permitted.

Question (Rav Acha bar Rav Huna): This implies that Hirhur is not k'Dibur. R. Yochanan forbids thoughts of Torah in a privy, i.e. for it is k'Dibur!

Answer: No, he forbids due to "v'Hayah Machanecha Kodesh."

Rishonim

Rif (Berachos 8b): They argue only about Keri'as Shma. All agree that one is Yotzei other Mitzvos (even if he did not hear himself), like the Beraisa says that one is Yotzei Birkas ha'Mazon b'Di'eved if he blessed in his heart. Rav Yoshiyah rules like the lenient opinion.

R. Yonah (DH Lo): If one may not say a Berachah or Tefilah, e.g. if his hands or the place are not clean, e.g. a Choleh in a dirty bed, he should think the words in his heart. He is not Yotzei, but he is rewarded for his intent.

Beis Yosef (OC 85 DH Lo): All the Poskim forbid even Hirhur in a place of filth. Perhaps R. Yonah does not refer to true filth.

Magen Avraham (62:2): R. Yonah discusses places such as the middle room of a bathhouse. The Shlah says that R. Yonah means to think about his obligation and regret that he cannot bless. R. Yonah's words connote otherwise.

Rambam (Hilchos Keri'as Shma 2:8): One must hear himself say Keri'as Shma. If he did not hear himself, he was not Yotzei.

Kesef Mishneh: R. Mano'ach says that he must be audible to his ears, i.e. say the words with his lips, and not read in his heart.

Rambam (Hilchos Berachos 1:7): For all Berachos, one must hear himself. If he did not, he was Yotzei, whether he said it with his lips or blessed in his heart.

R. Mano'ach: Keri'as Shma is mid'Oraisa, and if one did not say it audibly to himself, he was Yotzei. All the more so he is Yotzei other Mitzvos and Berachos (in this way).

Rosh (Berachos 3:14): Ravina derived from our Mishnah that Hirhur is k'Dibur, and anyone may be Yotzei through it. Our Mishnah is like R. Meir, who says that it depends on intent in the heart, or like R. Yehudah, who says that b'Di'eved he was Yotzei if he did not hear himself, but l'Chatchilah he must hear himself. For a Ba'al Keri, we rely on Torah law, and he is Yotzei through Hirhur. Rav Chisda says that our Mishnah holds that Hirhur Lav k'Dibur. It is like R. Yosi; if he did not hear himself, he was not Yotzei. Even R. Meir requires saying with the lips. Without hearing himself, it is called intent in the heart. The Beraisa that says b'Di'eved one is Yotzei Birkas ha'Mazon in his heart, i.e. if he said it with his lips but did not hear himself. R. Chananel says that the Halachah follows Rav Chisda, because R. Elazar and Rav Ada explain him. One is Yotzei Keri'as Shma only if he said it with his lips, even though he need not hear himself. Rav Chisda himself ruled like this! R. Yonah learns from Shabbos 150a that Hirhur is not k'Dibur.

Shiltei ha'Giborim (Berachos 8b:3, citing Ri'az): If one thought Keri'as Shma in his heart and did not say it with his lips, he was Yotzei.

Bach (OC 62:4): It seems that he learns from R. Yochanan, who forbids Hirhur of Divrei Torah in filthy places. I say that we rely on Tosfos and the Rosh citing R. Chananel; it seems that the Rambam and Semag agree. The Rambam in Hilchos Berachos and Semag (Aseh 27) say that one is Yotzei without saying with his lips only for Berachos, but not for Keri'as Shma, like the Kesef Mishneh explained in the name of R. Mano'ach. The Tur holds that even for Birkas ha'Mazon, one is Yotzei only if he said it with his lips, and the same applies to oither Berachos. It seems that the Poskim agree. The Shulchan Aruch (185:2) rules like this.

Note: R. Mano'ach says that Berachos are like Keri'as Shma!

Poskim

Shulchan Aruch (OC 62:3): One must say the words (of Keri'as Shma) audibly to his ears. If he did not make it audible, he was Yotzei, as long as he said the words with his lips.

Bach (3): The Gemara concludes that the Halachah follows R. Yehudah. L'Chatchilah, one must hear himself. This is mid'Rabanan; it is unlike R. Meir.

Mishnah Berurah (4): The Rashba brings the Ra'avad, who holds that mid'Oraisa, l'Chatchilah one must hear himself.

Bach (4): The Isur to think Torah in filthy places is not because Hirhur k'Dibur. Rather, it is due to "v'Hayah Machanecha Kodesh." In Keri'as Shma, it says "v'Dibarta Bam", to teach that Hirhur is not k'Dibur. This is why the Tur says 'for Keri'as Shma it is not k'Dibur.'

Bi'ur Halachah: Even for Keri'as Shma he was Yotzei, and all the more so for Berachos. Sha'arei Teshuvah and Birkei Yosef (185) say that most hold that if he did not hear himself, he was not Yotzei (Birkas ha'Mazon). This is astounding. Perhaps they mean that he was not Yotzei the ideal Mitzvah.

Kaf ha'Chayim (7): If one cannot hear himself because he is in a noisy place, Chesed la'Alafim (was unsure if he must scream in order to hear himself, or if a normal voice suffices, i.e. in order to fulfill the ideal Mitzvah. (Surely he is Yotzei in a normal voice.)

Shulchan Aruch (4): If due to sickness or another Ones, one recited Keri'as Shma in his heart, he was Yotzei.

Beis Yosef (DH Kasuv): Orchos Chayim brings this from the Yerushalmi, which learns from "Imru bi'Lvavchem."

Eliyahu Rabah (2): How could Ravina say that Hirhur is k'Dibur? If so, we need not expound to permit any language, like the Rashba says! Ravina: is not like Rebbi or Chachamim! Rather, he discusses a Ba'al Keri, who is Ones. The Halachah follows Rav Chisda, i.e. even b'Ones one is not Yotzei through Hirhur. I am astounded that the Shulchan Aruch rules differently.

Rema (OC 62:4): L'Chatchilah one should do so if he is in a place that is not totally clean (at the time for Keri'as Shma) and he cannot clean it, he should think Shma in his heart. If it is utterly filthy he may not think about Divrei Torah.

Taz (1): From here we learn that at night, if one is thirsty in bed and he cannot wash his hands and bless, he thinks the Berachah in his heart and drinks.

Mishnah Berurah (8): Mateh Yehudah disagrees. This is not Ones. He can get up and wash! We cannot learn from a case of illness or Ones. If he does not have water to wash and drink, or it is hard to get up due to the cold, he cleans his hands on the wall or anything that cleans, and blesses.

Mishnah Berurah (7): He was not totally Yotzei. We hold that Hirhur is not k'Dibur. Rather, when he cannot speak, he thinks Keri'as Shma in his heart. He will be rewarded for this. Since he was not Yotzei, when the Ones goes away, if the time for Shma did not pass, he recites Shma.

Mishnah Berurah (9): If the place is totally filthy, he does not think the text of the Berachah or Shma. Rather, he thinks that he is obligated, and feels pain that he cannot fulfill this. One should not drink in the bathhouse, even through Hirhur, for this is not Ones.

Gra (DH v'Af): A Medrash (Tehilim, Shochar Tov 5) says that David asked 'when I can speak, "Ha'azinah" (listen); 'when I cannot speak, "Binah Hagigi" (understand my thoughts)'. Yalkut Tehilim (627) says 'if you cannot pray, think in your heart "Imru bi'Lvavchem."'

Sha'agas Aryeh (7): If a Cheresh speaks but he cannot hear, can he be Yotzei Keri'as Shma? The Gemara connotes that R. Yosi and R. Yehudah both expound "Shma" to obligate hearing oneself, and they argue about whether this is Me'akev. Since a Cheresh cannot do this, all should agree that it is Me'akev for him! Tosfos (13a DH v'Chachamim) connotes unlike this. He says that the Halachah does not follow Rebbi (who expounds "Shma" - you must hear yourself) against a Rabim, and also, we rule that one who did not hear himself was Yotzei. We rule like R. Yehudah, who agrees that l'Chatchilah one must hear himself, like Rebbi expounds! Rather, R. Yehudah requires hearing oneself only mid'Rabanan; the verse is an Asmachta! Mid'Oraisa, l'Chatchilah one need not hear himself. Therefore, even a Cheresh can be Yotzei.

Sha'arei Teshuvah (2): Likewise, if one hears but cannot speak, he is Yotzei with through Hirhur.

Kaf ha'Chayim (9): All the more so, in a case of Ones one may be Yotzei through hearing Keri'as Shma from another.