My master…whatever he has, he has placed in my custody….How can I perpetrate this great evil? And I will have sinned against G-d.^[2]

These are two distinct lines of reasoning. First Yosef argues that submitting to the wife of Potiphar’s advances would demonstrate a horrible lack of gratitude to someone who trusted him so much. He then invokes religion: engaging in marital infidelity with her is a sin against G-d. How do these two relate to each other?

We begin with a pasuk in Tehillim.^[3] “I keep my feet from all evil paths, so that I will heed Your word.” I.e., the path is observably, objectively evil. Nonetheless, I avoid it not because I understand it to be heading in the wrong direction, but because You have instructed me to do so! Many mitzvos make sense to us, and we will gladly perform them because we understand them to be good. And we might easily refrain from some aveiros on our own, because we recognize the behavior to be wrong. What we should be doing, however, in all cases is acting because our Creator instructs us, and not because we follow our own lights.

Yosef meant similarly. He recognized the immorality of repaying his master’s confidence in him with betrayal. But he nonetheless emphasizes that his chief reason for rejecting Mrs. Potiphar’s advances is that he does not wish to sin against G-d.

Alternatively, Yosef might have been making the point of the Chovos Halevavos, who writes that every interpersonal aveirah is really two sins in one. There is the offense to another human being, and an additional sin to Hashem. Yosef here therefore included both of these sins in his explanation.

The Rambam^[4] makes an important distinction in the rule we just mentioned. When should we refrain from an aveirah only because of the Divine commandment, and not because of our own determination of right and wrong? Only in regard to “received mitzvos,” i.e. those that right-minded thinking do not obligate. Regarding these, it is fine to have leanings and desires to violate them, and refrain purely out of obedience to Hashem. Regarding aveiros, however, for which we ourselves can find compelling moral and intellectual reasons, it is improper to even think of violating them. Hashem wants us to be the people that naturally will be repelled by these actions, without having to quash our desires because of a Divine edict. (We should not have to remember the commandment lo sirtzach in order to refrain from emptying a magazine of bullets into a kindergarten playground.)

Adultery belongs to the first category. There is no compelling, logical reason to prevent two willing adults from exercising their autonomy in choosing their partners. But there is a huge caveat. Circumstances count. When the infidelity would mean a wanton disregard for the cuckolded husband who had bestowed much favor upon the paramour, and shown him much trust – then the adultery turns into an easily recognizable failure of both morality and proper sechel. It belongs to the second category of the Rambam.

For this reason, when Yosef refuses the lady’s advances, he first speaks of his refusal to repay the good of his master with evil. That moves the transgression from the first category to the second. The Torah uses the word ma’ein to describe that refusal. The Targum renders it sareiv, which is a particularly forceful rejection, as if to something completely out of the question! When she continues to pressure him, the Torah simply says that “he did not listen to her.” When she first announces her amorous designs on him, however, Yosef’s reaction is ma’ein – No way! I refuse to even think about it!

This explains as well the shift in tense in Yosef’s words. He first uses the future tense: “How can I perpetrate this great evil?” He then shifts to the past: “I will have sinned against G-d.” He means that not only would the actual doing of the deed be a great evil, but because it belongs to the second category of the Rambam, merely having entertained the possibility will be a great sin!

1. Adapted from Divrei Shaul, by Rav Yosef Shaul Nathanson, the Sho’el U-Meshiv ↑
2. Bereishis 39:8-9 ↑
3. Tehillim 119:101 ↑
4. Shemonah Perakim 6 ↑