Matters of doubt
על-פי התורה אשר יורוך ועל-המשפט אשר-יאמרו לך תעשה לא תסור מן-הדבר אשר-יגידו לך ימין ושמאל
You shall do according to the Torah that they rule for you, and the judgement that they tell you. Do not turn left or right from the matter that they tell you
The Rambam, also known as Maimonidies, learns from this verse the obligation to listen to the Rabbis. It comes out then that every Rabbinic mitzvah, obligation, or prohibition, are all included in the commanded not to turn from the matter that they tell you. That should make them all obligatory on a Biblical level in some way. To this asks the Ramban, also known as Nachmanidies, how could it be then that we have a rule in a Biblical matter of doubt that one must be stringent, but in a Rabbinic matter of doubt one may be lenient? If every Rabbinic matter is really Biblical, how could there be this distinction?
Some suggest a very simple explanation. Since the Rabbis can decree whatever they want, they can decree that one can be lenient in a matter of doubt. Meaning, built into every Rabbinic enactment, even if the obligation to listen to it is Biblical, is that if there occurs a doubt in this enactment, one can be lenient. However, the Chasam Sofer wants to suggest that an answer is found in the very verse where the Rambam is coming from.
The verse says not to turn from what the Rabbis tell us, not right, nor left. The Chasam Sofer suggests what this means we shouldn’t forbid that which they permitted, nor should we permit that which they forbade. This would be turning to the right or turning to the left. However, something that is neither right nor left, meaning something that is a matter of a doubt, the verse wasn’t referring to that. It comes out then that we were never commanded to listen to the Rabbis regarding a matter of doubt. This means then that in such a case we have every right to be lenient.
 Based on Chasam Sofer Al HaTorah to Deuteronomy 17:11
 Deuteronomy loc. cit.
 Sefer HaMitzvos Shorashim § 1; Mishneh Torah Hilchos Mamrim 1:1,2
 Hasagos HaRamban Al Sefer HaMitzvos ad. loc.
 Rashbatz in his Zohar HaRakiah Hakdama Shorash 1. In fact, Rav Gustman in his Kuntresei Shiurim Kiddushin § 24 points out that the Ramban ad. loc. himself proposes this resolution and rejects it
 The Ramban loc. cit. has other questions on the Rambam, including the idea that if there’s a dispute in a Rabbinic matter, we should follow the lenient opinion (Avodah Zara 7a). The Shev Shematessa 1:3 understood that the Rashbatz’s answer would not cover this latter question, as the one who rules stringently wouldn’t say that built into their decree is to be lenient in a matter of doubt. He has no doubts, so how could we ignore his opinion? Nevertheless, the Ohr Gadol § 45 sees no reason why the Rashbatz’s approach won’t apply here as well. We can simply say that Chazal decreed whenever there is a doubt on how to rule, we follow the lenient approach
 The Chasam Sofer says one could argue that regardless of this reading of the verse, the Rambam holds all matters of doubt are really permissible on a Biblical level (Mishneh Torah Hilchos Tumas Mes 9:12). In fact, the Shev Shematessa loc. cit. proves from the Ramban’s questions that the opinion of the Rambam must be true. However, the Rambam is stringent in doubts which are איקבע איסורא (Mishneh Torah Hilchos Shegagos 8:2; see Shev Shematessa 1:1-4). As such, the Chasam Sofer says his reading of the verse would cover those cases as well, such that if there was a Rabbinic matter of doubt involving איקבע איסורא, one could nevertheless be lenient