Q. Q. Re- above question. Why is it permitted to flip a coin to establish who has rights or is the owner of a property. does that not contravene the prohibition of not divining the future or the positive commandment of Tamim tichye?”
A. Rishonim disagree as to if one is permitted to use a goral or the casting of lots, to determine what is to be the future or to decide the next course of action. They deal with differences between relying on omens for the future, or for indications of the past, and If not permissible what are the prohibition transgressed.
Rambam (Avoda Zara 11) discusses the prohibitions of divination and necromancy together with witchcraft and sorcery and other prohibitions related to the ways of idolaters. He concludes with: “All these matters are matters of falsehood and deceit, and it was with these that the early idolaters made the other [non-idolatrous] gentiles deviate and follow them. It is not fitting for Jews …  to use such nonsense, or even to think that they are of any use… Because of this, when warning us against these nonsensical practices, the Torah says, ‘You shall be wholehearted (Tamim) with Hashem, your G-d.”
Rambam (ibid, 11: 8-9; Commentary to Mishnah, Avodah Zara 4: 7) rules that consultation with stargazers is included in the prohibition of divining (me’onen), or, alternatively, in the prohibition of reading signs (menachesh).
The Ramban (T. Meyuchasos, 283), however, sees the practice of stargazing in a different light. In his opinion, the practice does not violate any of the negative prohibitions defined by the Torah, because it is a matter of wisdom rather than a matter of divination and sorcery.
He rules that if one receives unsolicited advice from a stargazer, he is permitted to follow this advice, for instance, by increasing his performance of mitzvos so as to overturn the decree. Nonetheless, the Ramban rules that actual consultation with stargazers is prohibited, for it violates the instruction of tamim tihiyeh, the obligation to be wholehearted with Hashem.
On Sanhedrin (65b) Tanaim dispute the Biblical prohibition of using omens. The first opinion lists such omens as food falling from one’s mouth or a deer crossing one’s path. The second source lists studying the conduct, communication, or migratory patterns of fish or birds.
However, we find contradicting opinions. Talmud mentions omens such as a solar or lunar eclipse, which are a good and bad sign for the Nation of Israel, respectively. A number of Talmudic anecdotes (Chulin 95b) details signs and omens that were used by various Sages. Rabbi Yochanan, for instance, asked children which verse of the Torah they were studying. According to Rabbi Shimon ben Elazar, it is permitted to utilize a house, child, or woman, as a sign.
In addition to signs and omens, we do find that a number of Torah leaders over the generation employed different forms of goralos, “lots,” that involved opening the Torah or Tanach at certain places, in order to resolve difficult dilemmas. One of the most renowned of these goralos is the Goral Ha-Gra. Even today some continue to practice various forms of goralos. (See next question).
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a