But isn’t there a prohibition against looking at a woman’s beauty?

Looking at a woman’s beauty is straightforwardly forbidden because of concern about forbidden thoughts. That is what I was talking about. See Ritva at the end of Kiddushin.

I know it. It’s just that when people write publicly, thank God, about “it’s hard not to come to a prohibition,” usually they are not even talking about erotic thoughts (most of the public, unfortunately, is not on that level), but mainly about touching and the like.

That said, if looking at her beauty is forbidden out of concern for thoughts, how can you say that in the questioner’s case there is no fundamental prohibition? If the Sages enacted the enactment (by the way, in Beit Shmuel on the Shulchan Arukh it says this is from what is called words of tradition), then it really is forbidden and not just inadvisable, because in their view the distance between looking and thoughts justified an enactment. Or are you saying that the situation in which it is hard not to violate a prohibition is referring to the prohibition of looking at her beauty? After all, even a rabbinic prohibition is still a prohibition.

The wording of the Mishnah Berurah is: “But regarding the prohibition of looking, according to everyone, one who looks at a woman, even at her little finger, if he looks at her in order to derive pleasure, violates the prohibition of ‘do not stray after your eyes.’”
This is not because of concern about thoughts (“and guard yourself”) but because the very pleasure from nakedness [straying after the lust of the eyes] is itself forbidden by Torah law, so I do not see any possibility of being lenient here.

What enactment did they enact? There is no enactment here at all. There is a prohibition of thoughts, and one must be careful about things that lead to thoughts. That is exactly what the Ritva there was talking about, and therefore he wrote that if a person thinks he will not come to a prohibition, then there is no prohibition in these actions/situations.
And as for what the Mishnah Berurah wrote, it is possible that he means thoughts as pleasure from nakedness, in which case he is saying the same thing. And if he thinks there is a prohibition unrelated to thoughts, I disagree.

I saw this written in Peninei Halakha:
Two types of thoughts are forbidden: one, thinking about something that may cause a nocturnal emission, and the second, thinking about the sin of adultery. And so too in Igrot Moshe, Even HaEzer part 1, 69: “Now, there are two matters in the prohibition of thoughts: one is from the verse ‘and guard yourself from every evil thing’ (Deuteronomy 23:10), in Ketubot 46, where it says there: From here Rabbi Pinchas ben Yair said: A person should not think by day and come to impurity by night. This prohibition applies even regarding his wife, who is permitted to him. And likewise what is forbidden—to look at a beautiful woman even if she is unmarried, and at a married woman even if she is unattractive, and at colored garments of a woman he knows, and at animals when they mate, as stated also in Avodah Zarah 20 from this same verse—is not because he may think about committing a sin with her; rather, even if he will not think about committing a sin, it is still forbidden because it can lead to an emission of semen, which it is forbidden to emit in vain.

And the second is from the verse ‘after your eyes’ (Numbers 15:39), which is expounded in Berakhot 12 as referring to thoughts of sin. This is not because of concern about wasting seed, but rather it is a prohibition against thinking about committing the sin of sexual immorality, just as they expound ‘after your hearts’ as thoughts of idolatry, meaning to transgress the prohibition of idolatry, for the Torah forbade even the thought of transgressing in these matters…”

Honorable Rabbi, why should we care if he sins through wasting seed at night (if we say this is in his sleep), seeing as we rule that a sleeping person is exempt from the commandments?

Oren,
And all of that is included in the prohibition because of thoughts.

Z,
A sleeping person is exempt from the commandments, but not from the results of his actions during the day. In tort law we rule that a person is always accountable, even if he falls asleep with a stone in his lap. As I wrote here, this is even worse than placing oneself in a situation of coercion (where the halakhic decisors also disagree whether one is then considered coerced), because when one places oneself in coercion the result is the product of another factor that causes it. But here the result is the product of his own actions, except that the fruit ripens later. It is only a time gap.

Rabbi Michi, please look at Shulchan Arukh, Even HaEzer 21, in Beit Shmuel. https://he.wikisource.org/wiki/%D7%A9%D7%95%D7%9C%D7%97%D7%9F_%D7%A2%D7%A8%D7%95%D7%9A_%D7%90%D7%91%D7%9F_%D7%94%D7%A2%D7%96%D7%A8_%D7%9B%D7%90_%D7%90
A quote from there:
“(2) Or to gaze at her beauty: Rabbeinu Yona wrote that it is forbidden by Torah law, as it says, ‘do not stray after your eyes,’ and Maimonides holds it is rabbinic” (Haniga: up to here this is talking about looking at beauty, not thoughts!) “and regarding an unmarried woman, according to everyone it is from words of tradition, and thoughts, even about an unmarried woman, are forbidden by Torah law.” (Haniga: from the end you can see that until the very end he was speaking only about looking at beauty—where for a married woman, according to Rabbeinu Yona, it is Torah law and according to Maimonides rabbinic, and for an unmarried woman rabbinic according to everyone—and only the last sentence speaks about thoughts in general.)

I didn’t mean to come out like Rorschach, but I signed my name with the English letter r and the Rabbi read it differently. I liked it.
I agree with the Rabbi, but: a. I don’t think there is proof from tort law, because there one is liable even under coercion. So what difference is there between exemption due to coercion and exemption due to sleep? b. I agree with the basic idea, but the point needs to be clarified more: the exemption of a sleeping person is not essential but technical. He is still obligated even while asleep, but there is no consciousness to command. However, when the person is awake, there is someone to command even regarding the time of sleep. And therefore one must go to sleep in a sukkah. Does the Rabbi agree with this? (What is the Rabbi’s view regarding waking up from sleep for the sake of reciting the Shema? Is there an obligation?)

I won’t get into a survey of sources here, but I do not agree with that.
And there is no proof from the Beit Shmuel there either. First, because the Shulchan Arukh really is very stringent about this, and he even writes there later, “lest he come to thoughts.” Beyond that, the distinction is between looking that comes with thoughts and thoughts on their own, which are lighter. But looking that does not lead to thoughts may not have been forbidden at all.
Many have already discussed this, and I mentioned the Ritva at the beginning of Kiddushin.

r ( 🙂 ) As I said above, it seems I agree. But this is not a distinction between coercion and sleep (where there is simply no one to command, as you said). Sleep is a kind of coercion, but here through his actions he caused the result, as I wrote.

That it is “lest he come to thoughts” is certainly true. The question is whether because of that it was forbidden by a rabbinic decree (with “lest he come to thoughts” being only the logic behind it) or not.
The distinction you make is not acceptable to me. It is clear that “looking at beauty” that he is speaking about there is not “lighter thoughts” but simply taking pleasure in the woman’s beauty (which fits with the Talmudic passage about anyone who looks even at a little finger—the intention being when he means to derive pleasure, but not necessarily that he is actually thinking about a sin, according to the usual interpretation). Beit Shmuel brings medieval authorities who preceded the Shulchan Arukh, so it is not the Shulchan Arukh that is being stringent here but they are (and he says there is a rabbinic prohibition according to everyone!), and that should at least be mentioned in the answer—that there are stringent medieval authorities, and it was perhaps even the majority view, that this is entirely rabbinic even regarding looking at beauty.

Besides that, note that the Ritva there at the end of Kiddushin does not permit even someone whose inclination is subdued and under control to look at a woman’s beauty, but only to do things that might lead him to it (and he knows they will not lead him) to look even at her beauty. From this it seems much more reasonable to explain that the Ritva permitted what he permitted only for someone who “does not become aroused at all” = there is no concern in him of looking at a woman’s beauty.

And in any case, even if the Ritva says what you say he says—which does not seem right to me—why rule specifically like the Ritva against other medieval authorities here and against the Shulchan Arukh? (“Very stringent about this” is not an argument, it is only describing a situation that in your opinion emerges from his rulings.) At the very least, mention that there are medieval authorities—and perhaps even the majority—who hold that even looking at beauty is fully rabbinically forbidden.