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A man and a woman not married to each other are forbidden to be alone together in an isolated or inaccessible place. This is prohibited even if they are certain nothing inappropriate will happen. First, they can hope to be above temptation, but they cannot guarantee it. Second, people should not act in ways which will lead others to think they are sinning. Finally, even if these two people do not sin, there is a concern that others emulating their behavior may end up sinning.
Included in this prohibition are the cases of one man being isolated with two women (if neither is his wife or first-degree relative), or one woman being isolated with two men (if neither is her husband or first-degree relative). A person should avoid socializing with people who do not care about the laws pertaining to sexual modesty.
When colleagues of opposite genders share an office, they must make sure the door is never locked, and that it is likely other people will come in. If it is not likely, they should make sure to leave the door open so anyone passing by can see in. Similarly, when a repairman makes a house call and the wife is the only one home, or a consultant has a meeting with someone of the opposite gender, they must make sure people can see in. If not, they must leave the door open. Another way to avoid violating the prohibition of seclusion is by setting up a video camera with a live feed.
First-degree relatives such as parents and siblings (as well as grandparents) have no prohibition of being secluded together. A husband and wife during nidda are also allowed to be alone together, since they know at some point she will immerse and they will be permitted to one another. Nevertheless, since they are so close to each other and their desire can be easily aroused, the Sages established safeguards to help them protect themselves (9:8 above).
In addition to the prohibition of seclusion, men and women need to act modestly in each other’s presence. A man should not speak about personal matters to women other than his wife, nor should they go out to eat together or the like. The same applies to a woman with men other than her husband. A single person should not speak about these matters with someone of the opposite gender, unless that person is a potential spouse. All these rules are to ensure sexual desire is channeled into faithful love within the holy framework of marriage.
