Our Gemara on Amud Beis references the famous machlokes of Rabbi Yehuda and Rabbi Shimon regarding an unintentional act. If one performs an activity whose primary intent is permitted but along with it may come a forbidden act, according to Rabbi Yehuda it is forbidden and according to Rabbi Shimon it is permitted. 

Our Gemara discussed the case of a hot iron bar placed in the Mikvah to warm it for the Cohen Godol. The primary intention is simply to warm the water, however the cooling action might also contribute to a tempering of the metal, which would be a constructive act forbidden on Shabbos. (This is according to Tosafos Shabbos 41b “mecham”. See Chiddushei Rabbi Akiva Eiger Yoma 34b for an in depth discussion of the various interpretive possibilities.) Thus, according to Rabbi Yehuda the iron bar could only be Heated up to the extent that it does not reach a temperature that the sudden cooling will cause a tempering hardening process. However, according to Rabbi Shimon, The iron bar can even be hotter so that it might inadvertently become tempered and hardened, because it is an unintentional act. 

At its most basic, we see a difference between Rabbi Yehuda and Rabbi Shimon over the nature of the forbidden. Does the Torah only forbid something that is with primary intention or does it forbid even something that can reasonably arise from the act, though not the individual’s intention. In secular law as well, the severity of certain punishments depend on intent, that is a wish to commit the forbidden act and knowledge of the expected result. The Latin legal term is Mens Rea, which means guilty mind.

There is another famous machlokes of Rabbi Yehuda and Rabbi Shimon regarding the reasons for the mitzvos in the Torah and if they relate to halakhic distinctions or not (see sugya in Sanhedrin 21a.) 

Rabbi Shimon’s position was that one can presume a reasonable explanation for a commandment and then extrapolate applications and exemptions as it relates to case law. Thus, for example, the prohibition against taking a security from a widow debtor (Deuteronomy 24:17) only applies to a poor widow according to Rabbi Shimon. This is because presumably the prohibition was based on factoring in that since she was poor, he would have to let her use it when it was essential to her welfare (e.g. a blanket at night, as allowed to all debtors from Exodus 22:26). If a man were seen coming and going to the widow’s home it could lead to accusations against her virtue. Ergo, Rabbi Shimon held that the prohibition against taking a security only applied to a poor widow and not a wealthy widow since there would be no need to return the security as she had other bed linen in her home. On the other hand, Rabbi Yehuda held we cannot presume a logical reason for any commandment. At the very least, we cannot use that presumption to affect our legal rulings. 

These two major disputes between these great Tannaim that are referenced throughout Shas may be linked.

Rabbi Shimon holds that if a prohibition appears to have a logical reason though not explicitly stated by the verse, we can apply that reason to the halakha, as we saw by the wealthy widow’s security. This might be the same logic behind Rabbi Shimon allowing an unintentional act. After all, would it not be reasonable to say that the Torah only wanted to forbid actions that had mens rea, guilty mind? Alternately, Rabbi Yehuda, does not allow us to extrapolate even logically inferred reasons for the commandments insofar as it informs halakha. Thus, it makes sense that Rabbi Yehuda would also prohibit an unintentional act, as according to him, what is stated as forbidden, is literally forbidden.

We also could conjecture the reverse process. Namely it is Rabbi Shimon’s position about unintentional sin that informs his position on reasons for the commandments. Meaning, perhaps Rabbi Shimon argued as follows: Since it is logical (and possibly scripturally based as well) that one is not liable if the main intention was not to perform the forbidden act, does this not indicate that the Torah cares about intention?  If so, Rabbi Shimon might have reasoned that part and parcel of the intention would be to assume the nature and reason of the prohibition.

In any case, we do see Tannaim disputing matters of legalistic concern, that in many respects, have significant theological and psychological concerns.