Is it a sin for a man to have sex with women who aren't his wife(s)?

Question

This section of the Manusmriti on wisdomlib.org talks about what constitutes adultery.

In this section, it is clearly said that for a man, adultery constitutes engaging in sex with the wife of another man:

Those men who are addicted to intercourse with the wives of other men, the king shall banish after having branded them with terror-inspiring punishments.—(352)

A man who engages in secret conversation with the wife of another person,—if he is one who has been previously accused of similar offences,—should receive the penalty of the ‘first amercement.’—(354)

He who converses with ‘another’s woman’ at a watering place, or in a wilderness, or in a forest, or at the confluence of rivers,—incurs the guilt of ‘adultery.’—(356)

Nārada (14.6).—‘Indecent assault on another man’s wife is called violence of the highest order.’

One should not converse with the wives of other men, when forbidden. If, on being forbidden, he does converse, he becomes liable to be fined one ‘suvarṇa.’—(361)

Nowhere in this section is there a verse that explicitly says having sex with women other than your wife is a sin.

So, my question is, is it also adultery for the man when that man has sex with unmarried, promiscuous women?

This possible verse from the Narada Smriti permits sex with unmarried, promiscuous women:

12.78 Intercourse is permitted with a wanton woman, who belongs to another than the Brahman caste, or a prostitute, or a female slave, or a female not restrained by her master (nishkâsinî), if these women belong to a lower caste than oneself; but with a woman of superior caste, intercourse is prohibited.

But this doesn't mean any wanton women at any time, as there are caste and ashrama restrictions.

However, Medhatithi is of the opinion that it is a sin:

In the case of women who have not been wedded by any one, and live by prostitution, it is doubtful whether or not an expiation is necessary for having intercourse with them.

“What then is the right view on this point?”

The right view is that expiation is necessary.

Because the restriction (that one should he devoted to his own wife) has been directly enjoined, and expiation has been declared to be necessary in the case of one’s omitting to do what has been enjoined (11.41). ... The case of the ‘wanton’ woman has been already explained, and the prostitute also is an ‘unchaste woman.’

But the injunction "be devoted to your own wife" could simply be prohibitive to mean "avoid wives of other men."

Or, if the injunction "be devoted to your own wife" is actually meant to exclude all women except your own wife, the Narada Smriti verse that is permitting sex with promiscuous, unmarried women could only apply to unmarried Grihastha men, since if you don't have a wife, then you aren't bound by that injunction.

And a man actually enters Grihasthashrama when he takes his Samavartana bath, which is the final bath taken once you graduate from Brahmacharya.

Answer 1

So, my question is, is it also adultery for the man when that man has sex with unmarried, promiscuous women?

Defiling unmarried girls is regarded as equal to one of the 5 Mahapatkas (great sins). It is considered as equal to having sex with the wife of one's teacher (Guru).

Manu Smriti 11.58. Carnal intercourse with sisters by the same mother, with (unmarried) maidens, with females of the lowest castes, with the wives of a friend, or of a son, they declare to be equal to the violation of a Guru’s bed.

Manu Smriti 11.170. He who has had sexual intercourse with sisters by the same mother, with the wives of a friend, or of a son, with unmarried maidens, and with females of the lowest castes, shall perform the penance, prescribed for the violation of a Guru’s bed

A person who has done so must be avoided in rituals like Shraddhas .. See the following verse:

3.164. A breeder of sporting-dogs, a falconer, one who defiles maidens, he who delights in injuring living creatures, he who gains his subsistence from Sudras, and he who offers sacrifices to the Ganas,

This is one of the many verses which are describing the kind of persons who should not be invited in Shraddhas.

Few verses from Samvarta Smriti are as follows which agree with what Manu Smriti has to say:

For that vilest of men, who knows his own mother, daughter, or his own sister no atonement has been laid down. (160)

For knowing a maiden, one should perform this (i.e.* the Prajapatya) ; in holding sexual intercourse with an animal or a harlot, Prajapatya is laid down. (161)

A twice-born person, who knows his wife's friend, a maiden, his own mother-in-law, or his wife's sister, one engaged in Niyama, or one observant of a religious vow, should perform an ordinary penance and give away a milch-cow. (162)

So, why do you think it is not a sin and it is allowed?