GEMARA

(Mishnah): One who shaves the corners of the beard receives five sets of lashes, for two corners on each side and one below.

Makos 20a (Mishnah): He is liable only if he used a razor;

R. Eliezer obligates even if he used Melaket or Rehitani (a carpenter's plane or tweezers).

(Beraisa): Pe'as ha'Zakan is the end of the beard, i.e. Shiboles ha'Zakan.

(Mishnah): He is liable only if he shaved with a razor.

21a (Beraisa) Suggestion: Perhaps "u'Fe'as Zekanam Lo Yegalechu" obligates for shaving with scissors!

Rejection: One is liable for "v'Lo Sashchis" only if the entire hair is removed.

Suggestion: Perhaps one is liable for removing the hair with Melaket or Rehitani!

Rejection: "Lo Yegalechu." He is liable only for shaving that removes the entire hair, i.e. with a razor.

Question: Why does R. Eliezer obligate for Melaket or Rehitani? If he learns the Gezerah Shavah "Pe'as-Pe'as" (to equate "v'Lo Sashchis" written about Yisraelim to "Lo Yegalechu" written about Kohanim), he should obligate only for a razor. If he does not learn the Gezerah Shavah, he should obligate also for scissors!

Answer: He learns the Gezerah Shavah. He holds that also Melaket and Rehitani shave.

RISHONIM

Rambam (Hilchos Avodah Zarah 12:7): The priests of idolatry used to shave their beards. Therefore, the Torah forbids shaving the beard. There are five corners: the upper and lower jaw on the right and left, and Shiboles Zaken. One is lashed for each. If one cut all of them once, he is lashed five times. He is liable only if he shave with a razor, for it says "Lo Sashchis" - shaving that totally destroys the hair. Therefore, if he shaves with scissors he is exempt. One who is shaved is not lashed, unless he helped.

Rambam (8): One may shave the mustache, i.e. the hair on the upper lip, and also the hair that hangs from the bottom lip. Even though it is permitted, Yisrael do not totally remove it, rather, they shave it a little, so it will not interfere with eating and drinking.

Beis Yosef (YD 181 DH Kosav ha'Rambam): Perhaps the custom is is due to R. Chananel, who forbids the ends of the mustache. Surely the custom is to refrain from shaving. One may cut with scissors even the Pe'os of the beard, and all the more so the mustache.

Rosh (Makos 3:2): R. Chananel holds that where the jaw joins the temples is one corner, and also on the other side, and the two ends of the lips, on the left and right, and Shiboles Zaken below. Rashi explains that it is where the chin joins the bone, and one to the right of the chin and one to the left, and with the chin in the middle this is three. The other two are where the temples join. Some say that the jaw connects to the temples over a wide area, and both ends of it (on both sides of the face) are corners. The fifth is Shiboles Zaken. A Mishnah in Nega'im (10:9) says that the beard is from the jaw until the Adam's apple. One who fears Shamayim will fulfill all opinions and not pass a razor over the entire beard, unlike those who leave a small amount in each corner, for sometimes it is not exactly where the corner is.

Beis Yosef (YD 181 DH u'Mah she'Chosav v'Yesh, and Gra 181:18): The Tur (and also in his Piskei ha'R. Oshaya) says that R. Chananel holds that one corner is at the end of the beard on the throat. R. Chananel said only that it is Shiboles Zaken below. Rashi in Shevuos says that it is the thin bone on the chin below, for it sticks out like a Shiboles (ear of grain) in people whose beard is not full. Also Semak holds that under the chin is not a Pe'ah. Perhaps the Tur understood that the Rosh learns from Nega'im that the Adam's apple is a Pe'ah, but he should not have said so in the name of R. Chananel.

Bach (8): The Rosh brought the Mishnah in Nega'im to prove that R. Chananel refers to the Adam's apple. All agree that there is no Isur under the neck; just R. Chananel forbids the Adam's apple.

Rebuttal (Taz 4): The Tosefta forbids (on the sides under the jaw, from the jaw joint) until the Adam's apple, but not the throat.

POSKIM

Shulchan Aruch (9): The Shi'ur of the Pe'ah is even with the hair on the forehead, until below the ear, where the lower jaw goes out and separates. One should not touch (i.e. cut) any of the hair in this area.

Question (Tur): Why did the Rambam need to say that the Isur is due to pagan practices? Mitzvos are Hash-m's decrees. We need not seek reasons for them!

Beis Yosef (DH u'Mah she'Omar): The Rambam (Temurah 4:13 and elsewhere) explicitly says that Mitzvos are Hash-m's decrees. However, it is proper to seek reasons as much as we can for them, like R. Shimon.What we cannot understand is due to our limited understanding. Here, the Rambam learned from the surrounding Mitzvos, such as Nichush and tattooing, which are due to Nochri practices.

Taz (1): Since the Rambam holds that the Mitzvah is due to pagan practices, sometimes it is permitted, e.g. when needed for Shalom with the kingdom (like wearing their style of clothing - 178:2). The Tur holds that since it is not explicitly due to idolatry, we cannot be lenient. He did not suspect that the Rambam holds that we need not fulfill what we cannot explain, like the Beis Yosef thought!

Rebuttal (Panim Me'iros 2:79, cited by R. Akiva Eiger): The Rambam would not permit an explicitly Isur Torah due to Shalom Malchus. In Siman 178, the Torah did not specify an Isur. It authorized Chachamim to decide, therefore, they were able to permit where they saw fit! If also Hakafah could be permitted for Shalom Malchus, why did the Torah explicitly teach it? It is already included in the Isur of Nochri rites!

Note: Yosef shaved before he was brought to Paro, due to Kavod Malchus (Rashi Bereishis 41:14, from Bereishis Rabah). It seems that he just shaved his hair like the Targum (v'Sapar. Elsewhere, the Targum of Yegale'ach is that same root, i.e. shaving.) In any case, the Chasam Sofer (Miketz , DH va'Ygalach) said that fear of the king permitted an absolute Isur, i.e. shaving on Rosh Hashanah.

Shulchan Aruch (10): One is liable for shaving the beard only with a razor. It is permitted with scissors, even (close) like a razor.

Beis Yosef (DH Eino): Even Tosfos and the Rosh forbid scissors like a razor only for Pe'os ha'Rosh, but not for the beard. The Rambam says that one is liable only with a razor, but indeed without a razor it is permitted l'Chatchilah.

Rema: In any case people are careful when cutting with scissors to cut with the top blade, and not with the bottom, lest he cut totally with the bottom, and this is like a razor. However, it seems that one need not be concerned for the bottom of the neck, for it is not a primary place of the Pe'os.

Source: Piskei Tosfos (Makos 27,28), Terumas ha'Deshen 295, cited in Beis Yosef DH va'Doni.

Shulchan Aruch (11): There are five corners of the beard. There are many opinions about them. Therefore, one who fears Shamayim will fulfill all opinions and not pass a razor over the entire beard.

Rema: He should be stringent even under the neck.

Beis Yosef (DH v'Chosav Adoni): The Rosh says that one should be stringent for all the opinions. R. Yonah adds that meticulous people use only scissors even under the throat, even though it is not mid'Oraisa, for Chachamim forbade using a razor on the entire body, for this is like women do. Semak says that R. Tam forbids using a razor under the throat lest he come to shave the Pe'ah, but he permits with scissors.