Question: My nephew is in a polyamorous relationship, living in the same house with two women openly as a threesome. They are not married, but does this still count as adultery, or is it permissible?

An Orthodox view by Rabbi Alex Chapper

Coca-Cola is the world’s most popular soft drink and, understandably, its recipe is a closely guarded trade secret.

According to the company, only two employees are privy to the complete formula at any given time and they are not permitted to travel together.

When one dies, the other must choose a successor within the company and impart the secret to that person. The identity of the two employees in possession of the secret is itself a secret. Although this secrecy is clearly for commercial reasons, we can extrapolate from it the importance of exclusivity in relationships and specifically in a marriage.

The Hebrew word for marriage is kiddushin, which means “holiness” and it shares its root with other familiar terms such as Kaddish, kedushah and kiddush.

While we can define holiness as being something that is not mundane or even profane, it is much more enlightening to understand it as referring to that which is unique, special and exclusive.

By way of example, Shabbat is also described as “Shabbat Kodesh — the holy day of rest”, which reflects how we differentiate it from the other, more ordinary days of the week. If we treat Shabbat like any other day, then it is in danger of losing its holiness and that is why Jewish law protects its elevated status by prohibiting certain categories of creative activity on it.

Similarly, the intrinsic holiness of marriage is maintained by recognising that it is unlike any other relationship, the way in which two people, who are committed to each other, connect on an emotional and physical level, cannot be replicated towards anyone else outside of this couple.

The Torah conceived of marriage as the reuniting of two halves of a whole, as individuals we are incomplete until we commit exclusively to our “other half” and become “one flesh” (Bereshit 2:25).

Nachmanides explains that there is no more intimate a relationship than this and, according to Sforno, a married couple are to work together in such close union as if there were, in fact, only one of them.

In Judaism, we recognise that our physical world reflects the spiritual realms and so the expectation is that we learn from the special marriage bond between two people how to connect with God in a meaningful and fulfilling way, where there is no room whatsoever for other gods.

According to the Talmud, 40 days before a foetus is even formed, a heavenly voice announces who they will marry, which presumably is the source of the saying “a match made in heaven”, but it also reveals God’s intention for every relationship to be unique (Sotah 2a).

If the Coca-Cola formula is so valuable that it can be shared only between two people, how much more so is the holy institution of marriage.

Alex Chapper is senior rabbi of Borehamwood and Elstree (United) Synagogue

A Progressive view by Rabbi Jonathan Romain

My first instinct was to feel that this was not acceptable, but the more I thought about it, the more complex it became.

The usual assertion is that Jewish family life is based on a faithful union between two people. But that is not quite true.

In the Bible, polygamy was allowed and although it was banned under the edict of Rabbenu Gershom in the 11th century, it was only a temporary ban and has now expired (though it is still observed in practice).

Even then, it was only for Ashkenazi families, with Sephardi ones continuing to practise polygamy until modern times.

Other objections also fade away on closer inspection; your case of three people living together is not banned in civil law as there is no marriage contract between any of them, so it is not bigamy.

As for adultery, that is usually associated with covert betrayal, whereas polyamory is doubly different: first, it is open and without any pretence; second, it is with the active consent of all those involved.

It means that polyamory — which can be defined as partners living in a non-exclusive relationship — may not be as shocking as some people might hold.

It is also not as rare as may be thought — several studies on it as a modern phenomenon have already been published — though it is more prevalent in the US and with more cases among the under 40s than the over 40s.

However, there are also other, more practical aspects to consider. One is human nature and that jealousy, suspicion, favouritism and resentments can develop as time progresses.

Relationships can go wrong also in ordinary marriages, but the scope for problems in a threesome is much greater, and what works for a short while may not be successful in the long term.

There is also the problem of power: what if one partner would prefer an exclusive relationship with one of the other partners, but dare not say so for fear of losing that person? In addition, does the division of the genders involved make a difference to the control aspect?

What about any children? Would they benefit from having three parents or find themselves part of a tug-of-love?

They key for judging most unions nowadays, including gay marriages or unmarried couples living together, is: are they stable loving relationships? In polyamorous ones, I worry that if would be harder to give affirmative answers.

Jonathan Romain is rabbi of Maidenhead (Reform) Synagogue

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