Gemara

(Beraisa): Menachesh is looking for or acting according to omens like the following... 'do not collect the tax from me first, I do not want to pay my debt now, it is the start of the day or week or month.'

(Beraisa): "Lo Senacheshu v'Lo Se'onenu" refers to people who look for or act according to omens of weasels, birds and fish.

Horayos 12a (R. Ami): To know whether one will survive the coming year, he should hang a lamp during the 10 days of Teshuvah in a house without wind. If all the oil burns, this shows that he will live. If one wants to go on a trip and wants to know if he will return, he should stand in a dark house. If he sees a Bevo'ah d'Bevo'ah (a shadow of his shadow), he will return.

Rejection: He should not do this. Perhaps he will not see it, and he will worry, and this will spoil his Mazal (and cause that he not return).

(Abaye): Since we learn that omens are significant, one should eat on Rosh Hashanah gourds, fenugreek (or clover) leeks, beets and dates.

Chulin 95b: Rav went to visit his son-in-law. The ferry was coming towards him. He said 'I will have a good day.' When e arrived, he saw hanging meat. Rav kept watching it, but he did not eat from it, due to the Nichush.

Objection: Rav taught that a Nichush that is not like that of Eliezer ("if she will agree to give water to me...") and Yonason (ben Sha'ul, "if they will say 'come up', we will go"), is not Nichush!

Rav would check the ferry (if it came to greet him). Shmuel would check Safra. (Perhaps he opened a Sefer and read the first verse, like Shiyurei Berachah YD 179:6). R. Yochanan would ask a child which verse he is learning.

R. Yochanan decided to go to Bavel to see Shmuel. He asked a child 'what verse are you learning?' The child said "Shmuel died." R. Yochanan did not go. Really, Shmuel had not died. Hash-m did not want to burden R. Yochanan.

(Beraisa - R. Shimon ben Elazar): Even though there is no Nichush, there is Siman.

R. Elazar: This is only if it worked three times - "Yosef is missing, and Shimon is missing. If you will take Binyamin (every affliction will come upon me)."

Bava Basra 12b (R. Yochanan): After the Churban, prophecy was taken from the Nevi'im and given to lunatics and children.'

Rav Chisda's daughter illustrates prophecy of children. (Rav Chisda asked her if she wants to marry Rava or Rami bar Chama. She said 'I want to marry both.' (Indeed, she married Rami bar Chama, and after he died, Rava.)

Rishonim

Rambam (Hilchos Avodah Zarah 11:4): One may not be Menachesh like Nochrim. The same applies to one who makes a Siman for himself, and says 'if this occurs, I will do this matter. If not, I will not do it', like Eliezer did. Everything like this is forbidden. One is lashed for these things.

Rebuttal (Ra'avad): This is totally permitted. The Rambam erred about the Gemara 'any Nichush that is not like that of Eliezer and Yonason is not Nichush.' He thought that it means that those are forbidden. Really, it means that one should rely only on such Nichush. How could he suspect that they transgressed?!

Defense (Chidushei ha'Ran Chulin 95b DH veha'Omar): It is clear that the Gemara teaches that only such Nichush is forbidden, for this is why Rav did not eat! How can we explain Eliezer and Yonason? The Torah forbids only when there is no logic for the Siman. Then it is like Darchei ha'Emori. It is normal to say 'if it rains, I will not go out.' Eliezer and Yonason gave such Simanim. Eliezer knew that the Zivug for Yitzchak must be proper for him. She should be such a Ba'alas Chesed that she will want to give water also for the camels. Yonason thought that if the Plishtim say 'come to us', this shows that they fear ambush. Often, two or three brave people make many fearful people flee. Had they answered 'wait until we come to you', this would show that they are not fearful, and it would be improper to risk his life. The Gemara means that any Nichush like that of Eliezer and Yonason is permitted; other Nichush is forbidden. Rav did not decide whether or not to go based on the ferry. He merely considered it a sign whether he would have a good day. Asking a child is not Nichush. It is a form of prophecy, like it says in Bava Basra. However, Rashi says that Rav decided whether to go based on the ferry. Perhaps he did not totally rely on this, rather, he just added it to other reasons. Rashi says that there is not Nichush, i.e. one may not (totally) rely on it, but there is Siman (if it fails, he will not try again so much). I hold like this. Perhaps also the Rambam means this.

Tosfos (Chulin 95b DH k'Eliezer): The opinion that a Benei Noach is commanded about everything in the Parshah of witchcraft must say that Eliezer (did not rely on the Nichush; he) gave the bracelets only after hearing who her father is. The Torah says first that he gave; it is out of order. When he told her family, he said that he gave after hearing. We must say that Yonason would have gone anyway; he merely sought to encourage the youth with him.

Beis Yosef (YD 179 DH u'Mah she'Chosav v'Chen): Rashi explains that a Nichush in which he does not really (i.e. totally) rely on it, like Eliezer, who said that he will speak with her only if she will give water to him, is not Nichush. The Rambam explains that a Nichush is forbidden only if it is like Eliezer's. The Ra'avad says that one should rely on it only if it is like Eliezer's.

Kesef Mishneh: Amora'im (56b) argue about whether Kishuf is forbidden to Benei Noach. We hold that it is permitted, for Nochrim have only seven Mitzvos. This is why Eliezer was permitted. Yonason was a total Tzadik. Presumably, his Siman was merely to encourage the youth with him, but in any case he would have attacked. However, it seems that he relied on the Plishtim's answer. The Rambam did not mention Yonason, for he did not intend for Nichush.

Rambam (5): One may say 'this house that I built was a good Siman for me', or 'this wife that I married or this ox that I bought was blessed, and after buying it I became rich.' One may ask a child what verse he is learning, and if it is a Berachah he is happy and says that it is a good Siman. This is permitted, for he does not base actions or refrain from them due to this. Rather, he made it a Siman for what already was.

Rebuttal (Ra'avad): The Gemara did not discuss whether these are forbidden. Rather, one should rely on them only after three times.

Lechem Mishneh: The Rambam permits in any case. Also he must explain that it is a good Siman only if he succeeded three times. Rashi holds that "Yosef is gone, and Shimon is gone. If you will take Binyamin..." discusses three tragedies after the birth of Binyamin. How can the Rambam learn from here that the Siman of a child's verse must work three times? We must say that it shows that real good or evil is only if it happened three times.

Rashba (1:413): Yonason's Siman was not logical. The Rambam holds that it was forbidden. Surely it was permitted, like the Ra'avad says, for Hash-m brought a great salvation through him!

Poskim

Shulchan Aruch (YD 179:4): Regarding a house, child and wife, there is no Nichush, but there is a Siman.

Darchei Moshe (2): The Radak (Shmuel 1:14:9) says that one may make a Siman for himself. This is like the Ra'avad. Semag holds like the Rambam.

Beis Yosef (DH u'Mah she'Chosav Aval): Rashi says that the Siman of a child is if he succeeded in his first business deal after a child was born. If not, he will not persist, lest he not prosper. The Rambam and Tur explain that he asks 'what verse are you learning?' One does not act based on this. Rather, he is happy or sad based on the verse. This is difficult, for due to the verse, R. Yochanan did not go to Bavel! Perhaps he did not ask about the future, rather, if Shmuel already died. Rav Sheshes (Gitin 68a) acted based on a child's verse, together with a snort from Rav Chisda and prior suspicion. Semag says that we find many Gedolim who asked a child what verse he was learning, and acted according to this. It is like a prophecy.

Shach (5): Most Poskim permit to act based on the verse, for it is considered a small prophecy.

Gra (12): Normally, a Siman has meaning only if he made the Siman before it occurred. Regarding a house, child and wife, there is a Siman even if he did not make it beforehand.

Shulchan Aruch (OC 583:1): One should eat on Rosh Hashanah Rubiya (black eyed peas) and say 'may it be Your will she'YiRBu (will be many) our merits...'

Beis Yosef (DH u'Mah she'Chosav Rubiya): Rav Hai Gaon would say (a Tefilah) based on each matter, e.g. on Kora he would say 'YiKRa (He will tear) decrees against us.' The Tur connotes that he need not say anything. The foods themselves allude to this.

Gra (4): Mordechai (Reish Yoma) brings from Ge'onim that we eat fatty meat and eat sweets, so the new year will be sweet and fat, like it says in Nechemyah (8:10). Rashi says that we eat foods that grow quickly.

Mishnah Berurah (2): One should be aroused to Teshuvah when saying 'may it be Your will...', and repent with all his heart.

Mishnah Berurah (5): Surely, one must be very careful not to get angry during these days, for it is a great Isur, and also for a good Siman. One should be happy and trust in Hash-m, with Teshuvah and good deeds.

Kaf ha'Chayim (6): One may say 'may it be Your will...' even if he does not eat it, and even if he does not see it, for it is not a Berachah.