Our Gemara on Amud Beis discusses how the Torah does not recognize a marriage canopy (chuppah) or betrothal (eirusin) as components of a gentile marriage. Instead, a gentile marriage is ratified not through symbolic ritual but through cohabitation as husband and wife. Tosafos here raises a question: If so, why is Esav criticized for committing adultery with a betrothed maiden (Bava Basra 16b) if such a status carries no formal legal obligation? Tosafos answers that, even though there was no legal requirement, the act was still odious in God’s eyes—just as the Torah condemns Esav for rejecting the birthright (Bereishis 25:34), despite the fact that he was not commanded to follow any particular priestly code.
This introduces the fascinating idea of how much morality is intrinsic. It would seem that, according to the Torah, certain moral principles are self-evident. The Gemara holds a gentile responsible for knowing the Seven Noachide Laws, and if he is unaware, he is still liable because “he should have learned but (negligently) did not” (Bava Kama 98a). The Rambam applies this principle more broadly (Laws of Kings and Wars 10:1).
How do we understand the argument that “he should have learned”? Is this to be taken literally—meaning that ignorance is no excuse, and he was obligated to study these laws? Perhaps. However, I will highlight two different perspectives from Rashi and Ramban, each of whom, in their own way, suggests that this principle is also tied to an innate moral sense.
Rashi (Bava Kama ibid.) adds that “he should have learned derech eretz”—literally, the ways of the land, but more accurately translated as “customary decency.” Why does Rashi emphasize this point? It would seem that he holds the primary argument is that common decency and customary behavior are abundantly modeled by upright people. This exposure should naturally translate into a basic knowledge of the moral behavior legislated in the Seven Noachide Laws.
Ramban (Makkos 9a) adds another dimension: “He should have at least been in doubt as to whether something was prohibited and asked someone.” Here, Ramban makes a subtle yet critical point. How can we hold a person liable for not knowing all the details of the law? The answer is that he should have enough of a moral instinct to recognize when an action might be questionable and seek guidance. This suggests that there is an element of innate moral intuition.
For further study on this issue, see Emunos V’Deos III:1 and IV:4, as well as Shemoneh Perakim 6, which also discuss the concept of an intrinsic moral sense.
On a related topic, stay tuned for Psychology of the Daf, Sanhedrin 55, where we will explore whether one is held accountable for accidental heretical thoughts.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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Rabbi Simcha Feuerman, Rabbi Simcha Feuerman, LCSW-R, DHL is a psychotherapist who works with high conflict couples and families as well male sexual health. He can be reached via email at simchafeuerman@gmail.com