Klalei HaPoskim

Overview

In order to be privy to the nuances and mindsets of the Poskim, it is advantageous to understand the Klalim relevant to the Poskim, from the two Talmuds through the Rishonim to the Shulchan Aruch. The Machon Yerushalayim edition of the Yad Malachi is particularly helpful for this, as the Yad Malachi is fantastic for collecting all the ideas mentioned throughout Halachic literature and the Matnat Yado footnotes add many additional sources from those who came before and after him, as well as direct quotations of sources.

Safrut Chazal: Talmud Bavli and Yerushalmi, Tosefta, Midrashim, and Zohar

=== Bavli ===ma

1. Regarding intra-Talmudic Halachic decision making (Klalei HaShas), see Klalei HaTalmud (Talmudic Methodology).
2. "Sugya veDuchteh Adifah" - The Amoraim focused most on the precise presentation of the Halacha when discussing it in its proper context. When discussing tangential points, the they were not as careful to speak with complete precision satisfactory for inferring the Halacha from.

Differences Between the Yerushalmi and Bavli

1. Since the Talmud Bavli was written after the Talmud Yerushalmi, its codifiers were able to filter out the points they didn't think were accepted. As such, when the two contradict, we follow the Talmud Bavli, and some say we should never even be concerned for the Yerushalmi's statements altogether for this reason.
2. The Halacha follows the Bavli over the Yerushalmi wherever they disagree, but, if the Yerushalmi discusses a Halacha not mentioned in the Bavli, the Halacha follows the Yerushalmi. If it's a distinction not mentioned in the Bavli, then there's a strong argument to say the Bavli's omission is an indication of disagreement.
3. The Rosh writes how we only follow the Bavli over the Yerushalmi with respect to Halachot, such as Tuma veTaharah, Issur veHetter, Chiyuv and Pettur, but not things that are Tzorech Hashaah and have no ramifications on Dinei HaTorah. Those are subjective to the time, place, and needs of the people. Similarly, the Rashbesh says that with respect to Minhagim, we would follow the Yerushalmi.
4. If two approaches are offered in the Bavli and only one of them appears in the Yerushalmi, the Halacha follows that approach.
5. The Rishonim observe that the Yerushalmi in our possession is corrupt and enigmatic. At most, one person in a generation can crack its meaning. If a Baraita is quoted slightly differently in the Bavli from the way it's quoted in the Yerushalmi, the Ohr HaChaim claims one can accept the Yerushalmi's version and label the Baraita in the Bavli as Meshabeshta (corrupt). The Yad Malachi takes issue with this approach, in light of the general issue of textual obstacles in reading the Yerushalmi and the Tashbetz's claim that said even the girsa of the Yerushalmi is unreliable, not just the Halachot.
6. Given a Machaloket in the Bavli and a "Maaseh Rav" (anecdote about a Talmudic figure) in the Yerushalmi that takes a side, the Halacha follows the side expressed by the Maaseh Rav in the Yerushalmi.
7. The Poskim often try to harmonize the Bavli and Yerushalmi as much as possible.
8. Sometimes, when referring to topics in different locations, the Yerushalmi mixes up "here" and "there," because the topic appears more than once and the same text was copied/repeated completely from one location to the other without adjustment.

Differences Between Other Sefarim

1. When the Talmud and Zohar contradict, the Radbaz is well known for positing that one should follow the Talmud and Poskim.
2. When faced with a contradiction between the Yerushalmi and the Tosefta, the Rambam generally sides with the Yerushalmi. The Kessef Mishneh (Hilchot Maaser Sheni 1:10) explains that the authenticity of our set of Toseftas is questionable: they may not be the same Toseftas compiled by Rav Chiya and Rav Oshiya. The Peri Chadash adds that it's based on the Yerushalmi's later date of redaction. The Radbaz thinks the Rif takes the side of the Tosefta in such instances, while the Sdei Chemed and Korban Netanel think not so.
3. As we would follow the Yerushalmi against the silence of the Bavli, if there is a contradiction between a Midrash Rabbah and Yerushalmi, the Halacha follows the Yerushalmi over the Midrash.

Sefarim HaChitzonim (Masechet Semachot, Sofrim, and others)

1. Tosafot in a number of places writes how with respect to some Halachot, they follow Sefarim Chitzonim, such as Masechet Semachot and Masechet Sofrim, which were compiled later on, against the Talmud. They're called Chitzonim, according to the Bach because they are external to the Gemara, or, according to the Chidah, because they're even further removed from the Baraitot, which are already "outside," as their name suggests. Some say the Girsaot are also enigmatic.

Geonim

1. The term "Geonim" generally refers to those who lived between the Savoraim and the Rif, though the institution of Geonim did extend beyond then. Some say that the term Gaon is short for "Rosh Yeshivat Gaon Yaakov," while others claim it was reserved for those who were experts in all sixty Masechtot of Shas, corresponding to the Gematria of גאון.
2. The monograph on Hilchot Tefillin from the times of the Geonim is claimed by some to be super authoritative, as "the words of the Geonim are tradition" (דבריהם דברי קבלה) in that they had access to the first edition of Talmud Bavli, which was clearer than ours. At the same time, a number of Rishonim poke holes in the work and argue it shouldn't be followed when it contradicts Talmud Bavli.

Bahag (Ba'al Halachot Gedolot)

1. Often times, the Rishonim will disagree with the Bahag but conclude in favor of his ruling anyway, even if it's illogical, because "Devarav Divrei Kabbalah Hem." Because of the tradition stemming from the Amoraim, through the Savoraim, to him, the Bahag is granted special authority when the Gemara does not explicitly say otherwise; however, if the Rishonim feel the Gemara contradicts his words, then they freely disagree in practice, as well.
2. The Rishonim are uncertain if the Halachot Gedolot was authored by Rav Yehudai Gaon, who was blind, or by Rav Shimon Kayyara. Illogical rulings could be pinned on the former's students misinterpretation of their rebbe's words when writing his sefer. Some say Rav Shimon Kayyara wrote Halachot Gedolot, and Rav Yehudai Gaon wrote a different sefer known as Halachot Pesukot, while others claim they each wrote a sefer called Halachot Gedolot.

Rif

Practical Focus

The Rif generally quotes only relevant passages of the Gemara and leaves out points that aren't accepted at the end of the sugya. That said, there are some exceptions to be aware of.

1. Even though the Rif generally only records Halachot that are relevant nowadays, for example, to the exclusion of Kodashim, if a Halacha that is generally relevant has a detail that is not, he will write the entire Halacha including the detail. Moreover, if there is some relevant Halacha or Chiddush to derive from the irrelevant Halacha, then that Halacha will be included, as well, but practical but uncommon Halachot will not be recorded.
2. If a din that does not appear to be subject of debate in the Gemara is only recorded partially in the Rif, it's an indication that the Rif holds the omitted segments are not accepted in practice.
3. Periodically, the Rif will quote a Tosefta by opening with Tanu Rabbanan, because the end of that Tosefta is quoted in the Gemara.
4. When the Gemara presents two Baraitot that each derive the same Halacha but from different sources (Tanya and Tanya Idach), the Rif will quote both.
5. However, some say he will not quote a Baraita that is not in line with the accepted Halacha.
6. If the Gemara presents an answer that unanimously resolves a difficulty in the Mishna but then continues to present additional resolutions from other Amoraim, which we would assume like in practice, the Rif will still quote the unanimously agreeable upon answer, even if it's not LeHalacha.
7. The Be'er Sheva advises one to not be surprised if the Rif omits the okimta of the Gemara in favor of his own original understanding, as he rathers to minimize Machaloket than quote the Gemara. The Yad Malachi argues lengthily against this approach and posits that the Rif merely omits Gemaras he feels to not be Aliba deHilcheta. The Rif and Rambam aren't Amoraim who have the ability to decide unresolved issues in the Gemara!
8. Similar to the rule of Stam vaYesh in reading Shulchan Aruch, when the Rif states that the Halacha follows a certain ruling but there are those who disagree, he intends to rule like the former and is only sharing the latter to transmit the rulings of earlier generations.
9. If the Gemara presents an alternative answer (איכא דאמרי), the Rif will pasken like it instead of the first answer, even if the second answer is more stringent and the case is only of DeRabbanan nature.
10. Unless explicitly stated by the Rif that one should be stringent, the assumption is that a lenient approach is taken with unresolved inquiries of the Gemara (Tiku)
11. Similar to Rashi, the Rif will only explain a Halacha with the words כלומר or פירוש to offer specifically this interpreation over a possible alternative one that would be subject to some question.

Rav Hai Gaon

1. "The Gaon" in the Rif's jargon most probably refers to Rav Hai Gaon.
2. When the Rif cites a ruling of Rav Hai Gaon without explicitly agreeing with it, the Raavad and Rosh believe that he is disagreeing, while the Ramban and Rashba argue he is agreeing since he didn't state otherwise. The Yad Malachi finds that the Rashba is more logical, a great number of Rishonim side with him on this matter, and the former opinion isn't so clear in the first place.
3. After presenting a Machaloket, if the Rif concludes with citing Rav Hai Gaon as taking a certain side, that would indicates he agrees with that side, as well.

Misc.

1. There is controversy regarding the reliability and authorship of the Rif's responsa.
2. Rabbeinu Yitzchak ben Yaakov Alfasi, the Rif, had a grandson, Rav Yitzchak ben Reuven, who is known as the Baal HaShe'arim. Some Poskim weren't aware of this and mistakenly posed contradictions between the writings of the two.

Rambam

General

1. The Maharashdam believes that since the Rambam saw the other opinions on each issue and still decided the way we did, we should follow his rulings (analogous to the Radbaz and the Rif). On the other hand, a number of Ashkenazi authorities feel that the Rambam is a minority in the face of the Baalei HaTosafot.
2. One cannot pose questions from Tosafot's logic against the Rambam. Gavra aGavra KaRamit?!
3. The Rivash and Rosh warn that one who attempts to rule on practical matters solely from Mishneh Torah without understanding its Talmudic context will likely mistake Assur for Muttar and Muttar for Assur, thinking he understands the material. At the same time, the Rambam's explicit intention was to write the Halacha so clearly that one need not be bogged down by the confusing Sugya and need only Mishneh Torah to know how to act, so some Acharonim, such as the Ohr HaChaim and Baal HaTanya are less concerned. While that is true, the Rambam himself explains in a letter that he did so for people for whom understanding the Gemara was beyond their reach.
4. Seldom does the Rambam disagree with the Rif, so one should not assume so unless there are already a great number of Rishonim for him to side with.

Mishneh Torah

General Approach

1. In Mishneh Torah, the Rambam focuses on relaying rulings explicated in the Gemara in a lucid way, while leaving out rulings that can only be inferred but aren't stated explicitly.
2. The Rambam's style is to write only what it says in the Gemara and not the interpretation, but his intention is to for the interpretation of the Gemara to be applied to his words, as well, though some disagree.
3. It's abnormal for the Rambam to omit a din dealt with explicitly in the Talmud and instead write a different idea not mentioned in the Talmud that implies the one mentioned explicitly.
4. Counts of the number of Perakim, Halachot, Mitzvot, etc are provided in Mishneh Torah to facilitate memorization, not to imply additional ideas.
5. The Rambam will rule like a Halacha found in the Sifrei if it's not contradicted by the Talmud.
6. Every word of the Rambam is written with tremendous precision and exactness, enough for one to infer from his words as one would from the Gemara itself. Similarly, the Maharalbach warns that one shouldn't rush to reject the Rambam for coming off as against the Gemara, but should rather pin the in-congruence on our own lack of understanding.
7. One cannot infer from the presentation of a ruling in one section of Mishneh Torah and its absence in another seemingly appropriate section that it only applies in one and not the other, as the Rambam's goal is to present the Talmud's rulings in their wording in their appropriate place. For example, a Halacha in Terumot that might also fit in Maachalot Assurot cannot be assumed to only apply in Terumot and not Maachalot Assurot given its presence in the former and absence in the latter. This is, however, a valid tool in reading other Poskim, such as the Tur.

Writing Style

1. The word Assur is used even when referring to Dinim MiDeoraita that would warrant Malkot.
2. "MiPi HaShmua" refers to a Halacha whose source is not explicit in the Torah, and "MiPi HaKabbalah" refers to Halachot learned from Pesukim in Neviim.
3. The term "MiDivrei Sofrim" can refer to Dinim MiDeRabbanan, as well as any Din MiDeoraita not stated explicitly in the Torah, such as one derived via the thirteen Middot, because without the Chachamim it would not be understood.
4. Consistently marking each Din as a Gezeirah or Halacha LeMoshe MiSinai is not a priority for the Rambam: sometime he mentions the Din's classification, while other times he does not.
5. The Rivash argues that the Rambam will refer to a Takkanat Chachamim as "Torah," such as in "Lo Hikpida Torah" in reference to the Ne'emanut of an Ed Echad, while others disagree.
6. When the Gemara presents more specific arguments predicated on accepting one of two possible assumptions - "Im Timtzi Lomar" - the Geonim and Rambam understand that the Halacha assumes like that assumption. Some say this is only true if the Gemara did not leave the very same uncertainty pending with a "Tiku" elsewhere, while others argue the opposite. The two levels of the Im Timtzi Lomar cannot be interchangeable, meaning if assuming A over B and then asking C over D is equivalent to assuming C over D and then asking A over B, this rule does not apply for the Rambam. The words must also be explicit in the text of the Gemara, so two subsequent questions, one building on the previous, would not be subject to this rule. The Poskim dispute if this is only true when the Amora in the Gemara himself uses these words to navigate the situation or if it's even true when the omniscient narrator of the Sugya does so externally of the Amora's words. Some say that the Rambam will not follow Im Timtzi Lomar if the Gemara explicitly assumes the opposite idea to be true.
7. If the Gemara presents two opposite understandings and then rejects one, the Rambam will formulate it in a way that accepts the accepted one and implies the rejection of the rejected one.
8. Often times, answers presented in the Gemara in rejection of a difficulty are omitted by the Rambam in favor of the simple meaning of the Mishnah, Baraita, or Amoraic statement.
9. It is not uncommon for the Rambam to pin a ruling on a Pasuk not mentioned in or even rejected by the Gemara, because he felt it to be simpler or more acceptable, especially if there's no practical difference.
10. In a few places, the Rambam employs a Talmudic phrase to mean something different from what it does in the Talmud.

Connections to Other Works

1. Though the Rambam never relies in Mishneh Torah on what he already wrote in Peirush HaMishnayot, he does rely on what he wrote in earlier sections of Mishneh Torah, and perhaps even later ones, or, at least, in that chapter.
2. When a contradiction is found between the Perush HaMishnayot and the Mishneh Torah, the Halacha follows Mishneh Torah, which was written later and as a set of rulings, not a set of elucidations of the Mishnah.

Sefer HaMitzvot

1. The focus of Sefer HaMitzvot is not to determine which Mitzvot are part of the 613, not to present a comprehensive of accurate representation of their Halachot and details. Therefore, when studying Sefer HaMitzvot, questioning the count of Mitzvot is wholly acceptable, but questioning the details of the Mitzvot is not. The Mishneh Torah was written to address those details, and, even if there are distinct differences, it's always possible that he changed his mind over time.
2. There's a debate regarding if specific Rishonim such as the Samag, Maggid Mishneh, and Migdal Oz saw the Sefer HaMitzvot, as it wasn't translated from Arabic to Hebrew for some time. Later Acharonim culled lists of instances in which each of them cites the Sefer HaMitzvot to dispel those claims.

Perush HaMishnah

1. In Perush HaMishnayot, wherever there is an opinion that misleadingly seems to be the minority one but is, in fact, the one the Halacha follows, the Rambam will buttress that opinion by writing of its truth or singularity or the like to indicate that the Halacha does indeed follow it.
2. Sometimes our translation of Perush HaMishnayot will refer to a din as being MiDeRabbanan, but it's probably just a mistaken translation of "MiDivrei Sofrim."
3. The Ramban did not have the Introduction to Perush HaMishnayot available to him, as Hebrew translations of the Arabic were not yet available in Spain, according to the Yad Malachi, who posits that had they been available, the Ramban would not have been as quick to argue.

Ra'avad

Disambiguation: It's important to be aware that there are three individuals known as the Ra'avad: R' Avraham ibn Daud of Spain, author of Sefer HaKabbalah; R' Avraham ben Yitzchak Av Beit Din of Narbonne, who wrote the Sefer HaEshkol; his son in law, and R' Avraham ben David of Posquières, author of the Hasagot on the Baal HaMaor and Rambam, Baalei HaNefesh, and quoted extensively by Rishonim. Here, we also refer to the third one.

1. In a dispute between the Rambam and Ra'avad, some argue the Halacha should be treated as a Safek, while others favor the Ra'avad when he is more stringent than the Rambam, and still others are willing to be lenient like the Ra'avad against the Rambam.
2. When the Ra'avad presents a dissenting opinion with the opening of "Yesh Mi SheOmer," the Tur seems to think he actually paskens that way, but the Beit Yosef does not.
3. In his inimitable style, the Ra'avad's critiques of the Rambam should not be seen as personal attacks to belittle the Rambam but rather as means of raising the red flag to warn people not to follow the rulings he felt the Rambam was mistaken in presenting.
4. Neither the Rambam's Perush HaMishnayot nor Moreh Nevuchim were present before the Ra'avad, as they had not yet been translated from Arabic to Hebrew.
5. "Gedolei HaMefarshim" and "Gedolei HaMagihim" refer to the Ra'avad.

Sefer Mitzvot Gadol (Semag / Samag)

1. When quoting the Gemara, the Samag will often paraphrase to make the language flow more quickly.
2. The Samag draws heavily from the Rambam for the most part and entirely from his teacher, the Sefer HaTerumah, whose Maftechot he copied letter for letter. When in agreement with the Rambam, he writes so implicitly, and he only disagrees when out-rightly quoting the Rambam by name.
3. At the same time, most of his words are based on the Tosafot Shanz, and, for some reason, he does not seem to have seen the Tosafot Tuch.
4. The Bach says the Samag's way is to rule like the Ri Baal HaTosafot.
5. There's a debate if the Samag saw the Rambam's Sefer HaMitzvot or parts of it.

Rashi

Fundamentals

1. Rashi, colloquially known as "Kuntress," always takes the simplest Peshat of the Gemara, even if it's not in line with the accepted Halacha - even a Hava Amina rejected by the Gemara itself later on!
2. Along the same lines and by no means in disparagement of Rashi, the Radbaz alerts us that Rashi is primarily a Mefaresh, not a Posek, so much so that he doesn't even register as a Shitah when deciding a Machloket between Rishonim, such as the Rosh and Rambam., though some disagree.
3. In his inimitable and calculated pithiness, Rashi negates numerous difficulties with the understanding of the Gemara with just a few words. This is very much part of Rashi's claim to fame.
4. Rashi made multiple editions of his commentaries, which accounts for the apparent contradictions.
5. One cannot pose the tradition of the Geonim as a question on Rashi - "Gavra Agavra KaRamit?!"
6. Whenever Rashi uses the words כלומר he is offering that particular interpretation where one would have been able to offer an alternative one.
7. When Tosafot attacks Rashi with a series of difficulties from later Masechtot, one could argue Rashi assumes the Gemara at this point isn't working with them in mind.

Works Not by Rashi

1. The commentary on Divrei HaYamim is not by Rashi.
2. The commentaries on the side of the Gemara where Rashi should be on Masechtot Meilah, Nazir, and Nedarim, are not by Rashi.
3. There is a debate among Acharonim if the commentary of Rashi on Masechet Ta'anit is authentic or not; it seems that many Acharonim assume that it indeed is by Rashi.
4. The commentary Rashi on the Rif was compiled by a later student based heavily on Rashi.

Tosafot

Jargon

1. Beyond the surface level understanding of their words, the Rishonim imbued layers of implicit teachings in their words. There is often what to learn from inference, in addition to the basic understanding.
2. Sometimes Tosafot will argue "Ein Lehakshot" - not to pose a question - but not provide the reasoning, thereby leaving it to the reader to derive the answer or they find it in a parallel Tosafot.
3. Even though Tosafot often poses a question with "Im Tomar" and answers it with "Yesh Lomar," there are instances where the question will be asked in the formal manner but left unanswered.
4. If the primary answer presented to Tosafot's question suffers from a difficulty, an alternative answer will often be offered, prefaced by "הבה מצי לשנויי" or "הבה מצי לתרץ", that isn't subject to the other answers difficulty. This alternative answer, however, is not accepted, as it itself is vulnerable to a much greater challenge, which only the primary answer is safe from. In other words, if the main answer isn't perfect, another, weaker answer that resolves the difficulty with that answer will be suggested but not accepted, because it's subject to much stronger questions.
5. In instances where two answers are offered without quoting one of the Baalei HaTosafot by name, the second answer will only be prefaced with "ועוד" if it doesn't directly contradict the previous one. If the first answer is by a named Baal HaTosafot, though, then the word "ועוד" would be appropriate regardless of the answer, to indicate that this answer is also from the aforementioned Baal HaTosafot.
6. In terms of deciding which of two answers to follow, the Sheyarei Kenesset HaGedolah claims the first answer is ikar; the Chazon Nachum disagrees.
7. Sometimes Tosafot will pose a question with "Teimah" and leave it unanswered but not also "VeTzarich Iyun," because the answer was obvious.

Authorship

1. It is not uncommon to discover contradictions between comments of Tosafot across different Masechtot. For example, in one place, Tosafot will leave a question unresolved, while, in another place, it will be answered, and stil, in another location, a different answer will be presented and the other one rejected. Each side of that contradiction is in fact representing the opinion of a different Baal HaTosafot. Similarly, when two Poskim each associate a different understanding with Tosafot, one could explain that they're referring to different Baalei HaTosafot.
2. Even within a Masechet, sometimes there are missing comments of Tosafot or comments of other Baalei HaTosafot mixed in, the latter of which leads to contradictions within one set of Tosafot comments. Regardless, we try to reconcile the differences as much as possible.
3. The Maharshal has a well known illustration of how Rabbeinu Tam had around eighty students of incredible caliber.
4. The Tosafot commentary on most of the Masechtot studied originates with the Tosafot compiled by the Rash MiShantz, a compilation known as the Tosafot Shantz. However, our version was abridged by R' Elazar Tukh, whose redaction is known as the Tosafot Tukh and whose goal was to elucidate the give and take of the Gemara, not decide Halacha. Nevertheless, we follow the Tosafot Tukh over the Tosafot Shantz, because the Tosafot Tukh came later.. In fact, some say that we should follow the Tosafot on the more major masechtot, such as Yevamot, over the Tosafot on smaller Masechtot, because the former are from the Tosafot Tukh.
5. The Tosafot commentary to Yoma comes from the Maharam Rutenberg.
6. There is a debate if Tosafot and Rabbeinu Tam are considered two separate entities or not with respect to Kim Li and other Halachic calculations.

Misc.

1. Chochmei HaTzarfatim according to many refers to Baalei HaTosafot, although some are unsure.

Rosh

General Style

1. The Piskei Rosh are essentially summaries of the Tosafot on the Daf, so each can be used to complement the other in terms of understanding and drive. Where Tosafot is vague and the Rosh is clear or vice versa, one can rely on the clearer explanation to be a worthy interpretation of the vague one's words. Often times, the Rosh does not deviate from their position.
2. The Rosh primarily focuses on Sevarot accepted leHalacha and ignores those that are not. According to the Kenesset HaGedolah, if he presents two positions without deciding, it's because he's unsure which should be accepted. Sometimes, he'll present two interpretations, because he thinks they're both true. As such, his position will be vague, so we can logically infer he follows the majority of Poskim. Additionally, his son, the Tur, has the credibility to tell us what his father's position was in practice.
3. The Rosh mainly is drawn after the Rif except perhaps by explanations of Mishnayot, in which case he often prefers the Rash's understanding.
4. The Rambam's understanding of Im Timtzi Lomar as Halacha is not accepted by the Rosh, who posits that even those who accept it must admit that further levels are only accepted if they are consistent with the positions of the previous ones. Bach argues that Rosh will agree that when presented with four questions, two of which are Im Timtzi Lomar, that their standing out indicates the Gemara is following them.
5. An additional answer or through will be introduced with merely a "Vav," such as "וקמשמע לן" - and we also learn.
6. If an elucidation of the Gemara is not presented by the Rosh against Rashi, we assume he agrees with Rashi.
7. The breakup of Shu"t HaRosh into Klalim was done by later individuals, not the Rosh.

Contradictions

1. Just as Ein Seder LaMishnah in the days of Tannaim, meaning they didn't compile Shas in the order it now exists in, so, too, Rishonim didn't necessarily learn and write on Shas in order. It's therefore possible for an initial position to be written in a commentary to a later Masechet and the retracted corrected one to be presented in an earlier Masechet. This knowledge allows us to resolve difficulties in the Rosh and other Rishonim.
2. Given two contradictory statements in the Piskei HaRosh, some Poskim recommend following the one that fits with the Rif, but according to the Shach, if one is just an instance of parroting the Rif and the other is the Rosh speaking for himself, the latter should be followed.
3. To resolve contradictions between the Piskei HaRosh and Shu"t HaRosh, the Tur and his brother Rabbeinu Yehudah ben HaRosh say and the Bach postulates that the Piskei HaRosh were written later, so they should be followed over the Teshuvot. The Beit Yosef disagrees. The Maharil argues the Teshuvot should be followed, because they were formulated in the context of Horaah. The Kenesset HaGedolah writes how even according to the former view, if the conflicting Teshuva is based on additional, seemingly seen afterwards, sources, then we would follow the Teshuvah. Rav Yosef Yedid HaLevi adds that these rules are only applicable when it's an explicit contradiction, if not we rather reconcile the two.

Acceptance

1. Many testify to the grand acceptance of the Rosh throughout Spain, which the Kenesset HaGedolah argues is true even over the Rambam and Riaz. Meanwhile, the Radbaz recommends to at least follow the Rosh whenever the Rambam is unclear. He adds that the Halacha follows the Rosh against the Rashba, as the former came later.

Misc.

1. Uncharacteristically, the Rosh on Bava Kamma does not quote all the Gemaras and Piskei Dinim, but, rather, quotes the Gemara concisely when needed to discuss a novel idea.
2. Sometimes, the Hagahot Ashri on the Rosh is commenting on the Gemara itself, not the Rosh, and may even be disagreeing with him.

Tur

When Quoting the Rosh

1. When the Tur writes "My father decided this way" based on proofs, then the idea has import to other topics, as well, while "This is my father's conclusion" does not.
2. The Tur always follows his father's view when he writes "And my master, my father wrote this way, as well" (כן כתב אדוני אבי הרא"ש). In general, he follows the last position presented in a series of opinions, unless the first opinion was written anonymously. This is in line with the common rules of "Yesh veYesh" always following the last one and "Stam vaYesh Halacha KeStam."

Maggid Mishneh

1. The Kenesset HaGedolah writes that wherever the Maggid Mishneh says he couldn't find a proof for the Rambam, he doesn't agree. Some even say if he doesn't provide a proof, even without articulating that lack of finding, it's an indication of disagreement.
2. A contemporary of the Rivash, the Maggid Mishneh's allegiance to the Rashba is indicative through his throrough familiarity with the Rashba's opinions. Therefore, when in doubt as to how to understand the Rashba's opinion, the Maggid Mishneh's understanding is a valuable and acceptable window to determining what the Rashba means. Some say the opposite is therefore a valuable tool of understanding the Maggid Mishneh, as well.
3. His tremendous dedication to elucidating the Rambam gives the Maggid Mishneh credence in deciding what the true explanation is when the Rambam's position is debatable, according to the Radbaz.
4. The Rivash posits that when the Maggid Mishneh refers to the Rambam as "HaMechaber" and not "Rabbenu," it indicates lack of satisfaction with the Rambam's position on his part, but the Chidah argues that the verbiage is arbitrary.
5. The first three Perakim of Maggid Mishneh on Hilchot Gerushin (until Halacha 9) were not extant even in the times of the Maggid Mishneh himself; what we have printed was probably written by a student, not the Maggid Mishneh himself.

Migdal Oz

1. Many Acharonim, including the Maharshal, Radbaz, and Shach, have disparaging things to say about the Migal Oz, but the Yad Malachi minimizes the context of their complains to his responses to the Raavad's challenges to the Rambam. Indeed, the Koreh HaDorot praises the Migdal Oz, R' Shem Tov, for his great erudition and familiarity with Nigleh and Nistar.

Rashba

1. The Rashba had editions of Tosafot other than the one printed on the page of our Gemaras.
2. In Avodat HaKodesh, the Rashba writes "יראה לי" when referring to Halachot from the Yerushalmi, Tosefta, and anything else not mentioned in Talmud Bavli.
3. The Mishmeret HaBayit was written by the Rashba, but it wasn't in print at the times of the Beit Yosef, Rama, and Maharshal for them to see it.
4. The Baalei HaTosafot and Rashba share a similar approach, therefore, if the Rashba copies Tosafot, it's a sign of agreement.
5. The extent Shu"t HaRasha are a condensed version of the original.

Further Reading

• Koreh HaDorot, Ahavat Shalom edition with footnotes of the Chida
• Kenesset HaGedolah, Klalei HaPoskim
• Yad Malachi, especially the Machon Yerushalayim annotated edition
• Yair Ozen / Ein Zocher, by the Chida
• Shem HaGedolim, by the Chida
• Kol HaChaim, by Rav Chaim Palagi
• Sdei Chemed, Klalei HaPoskim (in some editions, vol. 6, page 55, and vol. 9, page 125 in others)
• Ein Yitzchak vol. 1, by Rav Yitzchak Yosef