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Why Two Parents Rather than One or Five?

In this post, Kalle Grill discusses his recent article in Journal of Applied Philosophy on how many parents there should be in a family.

Engaged parenting is hard work. That is one reason most of us prefer to have a co-parent. But why stop at one? As I argue in a recent article, I don’t think there is a good and general answer to that question. Some people are committed to an existing two-parent family, or to starting one, but there is no reason why society should endorse that family form as a norm.

We are used to thinking of parents as couples, not only romantically, but also as being two – no more and no less. Society is becoming more accepting of one-parent families, and some women now plan for solo parenting and seem to be doing fine. Three parents, however, still seems a bit much to most people.

There are historical explanations for these limiting thoughts. Most obviously, it used to be the case that exactly two people were involved in biological procreation. Though donor insemination took place in some clinics throughout the 19th century and gradually became more known and accepted, donations to single women have become prevalent only in the past decade or so, and only in some countries. Surrogacy, in which three people can be biologically involved, was first achieved in 1986 but is still rare. Interestingly, it is normally taken for granted even in surrogacy cases that there can be only two parents, though there are obviously three biological procreators.

Biology cannot fully explain the widespread presumption that a family should have exactly two parents. Adoption has taken place throughout history, and there is no biological reason for why adoptive parents should be any particular number. I suspect that the two-parent norm is underpinned less by biology than by the combination of two ideas – that parents should be romantic partners, and that one should only have one (official) romantic partner.

The second of these ideas – the monogamy norm – has been fiercely challenged by some philosophers lately, and defended by others. However, this idea by itself does not explain our inclination to prefer two-parent families. We can easily imagine a society where any romantic couple who were planning to start a family would look around for the third person to complete their team of parents. People in this society might think that you obviously need at least one parent who is not biologically related to the child. This simple thought experiment shows that, unless we take the position that all parents must be lovers (and why would we?), commitment to monogamy does not explain the two-parent norm.

It seems that the historical explanations for why we are used to thinking of families as having exactly two parents provide no moral reason for insisting that they do. Against this background, some philosophers have argued that it is illiberal or discriminatory to fail to recognize the many existing families where the number of people in a parenting role differs from two (e.g. Metz, Cutas, Brake, Brennan and Cameron). These philosophers typically invoke the idea of liberal neutrality – i.e. that the state, and perhaps public debate and opinion, should be neutral between different ideas about the good life.

However, I do not believe that liberal neutrality should be accepted as a restriction on what state and society should do. I believe that laws and social norms can be justified if they in general are conducive to good outcomes, and in particular if they are conducive to good outcomes for children. If these benefits are large enough, they may morally outweigh some unfairness to outliers who do not benefit. This is why I wrote an article where I try to assess the pros and cons of having a larger or smaller number of parents in a family. My thinking was that if some particular number, or some interval, is generally best for all involved, then society should push that number or numbers, by social norm-setting and/or legislation.

For some time, I believed (and argued in several talks) that families of 4-5 parents must be ideal: it would do much to ensure sufficient resources (material and emotional) for the children of the family, while each parent would have a relatively small work load, and at the same time all parents could still form an intimate connection to the child (attachment theory, for example, seems to allow at least this many attachment figures from an early age). In a recent blog post on ways to promote multi-parenting, Anca Gheaus seems to assume this perspective. However, I have come to doubt that 4-5 is the ideal number.

One reason to be somewhat skeptical of many parents is that each parent might be less engaged the more parents there are. In general, people tend to take less responsibility if there are many others around who are equally up to the task. With increasing numbers of parents, aggregate loss of engagement will occur with smaller individual reductions, for simple mathematical reasons. If a family of one parent adds a second, there will be more engagement in total as long as the two each contribute more than 50% of what the one contributed before the addition. However, if a family of four parents add a fifth, any individual reductions over 20% cause a loss of total engagement.

Another reason to prefer smaller families is that they face less risk of conflict. The more co-parental relationships there are, the more likely that one of them will go sour. Mathematics are again relevant, since the number of one-to-one relationships increase faster than the number of individuals: two people have one relationship, three people have three, and so on. (Solo parenting of course guarantees zero co-parenting conflicts, though it does not exclude the possibility of other conflicts that might affect the child.)

However, I do not find that these possible disadvantages for many-parent families are sufficient to outweigh the possible benefits. More parents do mean more material resources (unless some parents are so self-absorbed and/or destitute to cause a net loss to the children), and possibly more emotional resources as well. More parents also potentially contributes more variety, and should ensure against total loss of parenting, and against being exposed only to poor parenting. My article considers all of these dimensions, as well as some others.

If I had to choose a number, I would go for three. From my own experience of parenting with one co-parent, I think one more would have gone a long way towards making life easier and more enjoyable for both children and parents, without too much complication or dilution of responsibility. However, my considered opinion is that no number or interval is best in general. Society should therefore remain neutral, except to cap the number of parents at some number where it becomes psychologically and practically difficult for children to have intimate close personal relationships with more people.

The Journal of Applied Philosophy is a unique forum for philosophical research that seeks to make a constructive contribution to problems of practical concern. Open to the expression of diverse viewpoints, it brings the identification, justification, and discussion of values to bear on a broad spectrum of issues in environment, medicine, science, policy, law, politics, economics and education. The journal publishes in all areas of applied philosophy, and posts accessible summaries of its recent articles on Justice Everywhere.



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  1. Hi Kalle, very interesting post and paper! I tend to agree with you that there need not be any principled reason for an ideal number of parents. (Usually when I look for a number that’s because I also have in mind the potential desiderata of population control, so I try to figure out what the highest number of parents could be that’s compatible with sustained close relationships.) I do however have a distributional worry: if 3 or 4 involved parents is significantly better than one as far as the child is concerned, this seems to provide a ground for at least encouraging the larger family.

    And one more thought, about conflict. Is it clear that it always has the potential to increase in direct proportion with the number of parents involved? I can imagine two, or three, parents constantly fighting over how to do things because one of them is a trouble maker (say, emotionally immature. Many parents are, alas.) But the group dynamic if you have 4-5-6 people might/is likely to be such that the trouble-maker keeps a lower profile.

    • Thanks Anca!

      I agree with you that it would be good to get demographic fertility down further and faster, and that family forms could help in that regard.

      I guess I’m not sure that 3-4 parents is significantly better than one. If the one has enough resources, and a rich enough social network, it seems perfectly fine. But of course in general people don’t have this, or not sufficiently. But then there is the potential loss of engagement and the risk of parental conflict that speaks against higher numbers.

      Regarding conflict, I agree that the group dynamic may be different with different numbers of people, and that there may be general patterns here. As I say in the article (not in the blog post): “On the group and political level, the cost of coordination seems to depend almost entirely on what processes are used, and their suitability to the group to be coordinated”. So perhaps five member groups work well in general because, for example, it is rare that one person tries to dominate, which may be more common in smaller groups. I suspect there should be sociological research on this… But then we need to know how it plays out in the ver special situation of parenting, and there is very little empirical research on that. So one may speculate like this, but I think these interesting possibilities do not undermine the default assumption that more relationships entail a greater risk of conflict.

  2. Franc

    Hi there
    I co-parented (with my husband) one son who was born after my career was well established and successful. We had no active grandparents nearby, but I employed a women, similar age to me, whose own son was grown up. For several years she became our son’s “other mom”. She was with us for 10 years and is still part of our lives. Our son is very close to her. It was good fortune to have this arrangement and we all agreed he was the luckiest kid to have 3 parents.

    • Thank you Franc for this great example of a three-parent family.

      If I may ask, in terms of rights and responsibilities in relation to your child, I assume that you and your husband felt that these were mainly with the two of you? But even so, did you feel/think that the “other mom” had any moral rights and responsibilities? Such as a right and a responsibility to remain in contact with your child? If you like to share.

  3. Karen White

    Isn’t that why so many cultures raise kids in extended families, and/or tight’y connected neighbourhoods? Let’s not forget that a nuclear family of two parents raising their couple of biological kids almost entirely alone is a historical aberration. It so often leaves parents exhausted and miserable, and kids somewhat neglected or negatively impacted by how frazzled their parents are. Single parents either find or create tight community or become even more frazzled.

    Every arrangement that allows us to be happier when parenting and to raise happier kids should be on the table. Since children are now an option, not a necessity as hands to work or care in parents’ old age, nor the unavoidable result of wanting a sex life, we should think deeply about how to make that work better for all concerned.

    One advantage of getting parenting support from non-parents such as grandparents, cousins and neighbours is that the parents still get to do much of the decision making for their kids. No 3rd or 4th parent who feels their opinion has an equal weight. Considering how many couple fights are about how to deal w/the kids, that may be important.

  4. Maria

    It could be that divorce is actually an adaptation to the loss of tight knit, multi-age households and communities. A cell division of sorts in which, despite the initial trauma, the child ends up with four parents and their resources.

    • Karen White

      That would be a great outcome, but unfortunately often the kids end up w/ 1 and 1/8th parent, and fewer resources…. And there’s too often conflict about parenting decisions and styles, which without the relationship and good will of couplehood/friendship/family are rarely well resolved.

  5. Kamal

    Who counts as a parent seems to be a thing that we primarily reason about using archetypes. The archetypical parents are the woman and the man whose sexual intercourse led to the procreation of the child, and who properly have a certain kind of social relationship because of that biological relationship. The details of the social relationship differ across cultures, but for this discussion it’s enough to note that they seem to be rooted in the biological fact of natural parenthood. Other parents are parents by virtue of their closeness to this archetype. For example, adoptive parents are parents by virtue of taking on the social relationship normally accorded to natural parents but without actually being natural parents.

    Why is that biological relationship so important? Because mommies and daddies are where babies come from. Because that seems to go with the grain of our reproductive instincts. Because many cultures and individuals think that a person’s story doesn’t begin with that person; that story is the continuation of a story going back through her ancestry, and so her ancestry is important insofar as that story is important.

    Sperm donorship doesn’t break this model since, biologically, the sperm donor is as much a father as any man who inseminates a woman naturally. (A sperm donor’s closest non-artificial analogue is an absentee father following a one night stand.)

    Surrogacy and mitochondrial donation are more serious challenges to this biological basis of parenthood. If we take the biological relationship as seriously as the archetype does, we might want to insist that the surrogate mother in the case of surrogacy and the egg donor in the case of mitochondrial donations all be considered parents of the child and all have attendant social and legal responsibilities to the child. But we don’t for at least two reasons. One is that these procedures are still extremely rare. The other more important reason behind the actual practice isn’t intellectually neat in a way that’s similar to why we tend not to treat the father of a child conceived via sperm donorship like an absentee father after a one-night stand: these procedures are typically allowed in situations that would not comfortably accommodate such obligations. To take the case of surrogacy, for example, there isn’t much appetite for forcing a Mexican handmaid on every couple that wants to have biological children but can’t carry a baby through to term.

    As Karen White mentioned in a previous comment, many cultures already have a concept of extended families and neighbourhoods raising children (hence the saying that “It takes a village to raise a child”), and those can work quite well without actually wanting to call any of those other people parents. (Of course, when I say “parents” in this sense and throughout this post, I’m excluding grandparents.) Some cultures also have a concept of a legal guardian, which again recognises the role of non-parents in raising children. These provisions all make sense while acknowledging the biological restriction of parents as being exactly two people, one mother and one father, as being important for at least the reasons I gave above.

    To put all that another way much more briefly: even if we started using the word “parent” to refer to other people who raise a child but from whom the child is not immediately descended, that relationship would still exist and still be important, at least for most people.

    I think that answers the question in the title of this post.

    Given the recency of romantic marriages, I don’t think that romantic love has anything at all to do with this. Nor do I think that monogamy plays much of a role, especially given that this notion of parenthood is observed even in at least some cultures that formally allow polygamy (such as Islamic ones) or in which non-monogamy is common. It really seems to me to basically be about where babies come from.

    As for your suggestion that couples look for other adults to call parents that will help raise a child, don’t you think it’s already hard enough keeping a child’s two biological parents in the picture until the child leaves the nest without adding another, unrelated person to that equation?

    • Thank you Kamal for engaging with this topic!

      We seem to agree that the word “parent” is often used to refer to biological procreators and that the explanation for this is largely to be found in biology. We also seem to agree that there is no necessary connection between biological procreators and what I call “parents” and you call “people who raise a child”. As you mention, there are many biological procreators that are not parents, and not expected to be, and there are many parents that are not biological procreators and who are not therefore considered to be less responsible, or have less rights, or have less of a personal relationship to their children.

      My general take on value-laden words, i.e. words that have some descriptive meaning but that also carry a significant positive or negative connotation, is that their use should track their significant normative/evaluative meaning, even if this requires some modification of their descriptive meaning. Words like freedom, democracy and justice have been used in different ways in different times and places, but are still generally taken to refer to what we here and now think is valuable in their respective areas. For one illustrative example, the word “democracy” (dēmokratíā) as used in ancient Greece did not refer to a “demos” that included women. One could argue on this basis that the archetypical use of this word refers to the rule by male, free citizens (meeting in person etc.), and not to rule by the people as we understand this notion today (just to be clear, I here presume that this “we” includes me and you, Kamal, as well as most readers of this comment). If one grants this argument, one would then need another word than “democracy” to refer to those aspects of the form of government inherited from ancient Greece that we care about, or hold to have positive value.

      I have now expressed a normative position on the use of words, a note on how things “should” be. I am not a language scholar, but I believe actual use to a large degree works like this, with “democracy” one example.

      I wanted to explain my take on the use of words since I am using “parent” in the blog post without defining the term. I say “engaged parenting” in the first sentence in order to quickly and intuitively distinguish what I am talking about from other modes of parenting or being a parent, such as by being a biological procreator, or an absent material provider. But this is very subtle of course. In the article that inspired the blog post, I instead use a stipulative definition:

      “For the purposes of this article, I consider someone a parent to a child if and only if the following two conditions are met. First, a parent must have substantial moral rights and responsibilities towards the child, over time and over contexts, such that they are legitimately involved in the child’s everyday life and in all important decisions regarding the child. Second, a parent must be emotionally engaged with the child, such that the two of them have an intimate personal relationship over time.”

      My main interest is really how many people with these properties there should be in a family, more than how the word “parent” is used. I would actually be quite content if “parent” referred to biological procreators, as long as the word had very marginal significance in social and legal contexts, and there was another word that was used for what I characterize in the quote, that was more important in these contexts. However, I believe that my normative agenda will be better served by pushing further change of the notion of “parent” and so that is what I do.

      In the article, I am also careful to note that the word “parent” is used in different ways and that if one means something else by the word, one may come to other conclusions than I do.

      I agree with you that genetic ancestry is important. Most people in fact want to know their genetic ancestry and it is connected to identity and belonging for many people. It may also of be practically important in some medical contexts. In the article (not the blog post) I propose that “it has value to know the identity of one’s genetic procreators and to be able to get to know them, at least as an adult.”

      I just think that parenthood in my sense is even more important.

      I hope this makes my thoughts on this topic more clear. Thanks again for a challenging comment that prompted this possibly too long reply!

  6. A most interesting idea.

    You might want to talk to parents of the previous generation and the new generation in Bangladesh to actually glean information about this theory in practice.

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