The success of Homo sapiens clearly shows that most love relationships end up in some sort of arrangement between the two loving parties for spending lengthy periods of time together. When the two are a man and a woman, there's still the big chance a third, or forth etc person may come up, adding to the party. But the pair is not necessarily so to prove the theory that, when two come together, the result is not two, but three.
So the theory here is not the silly idea that two people together will eventually produce offspring, thus leading to the "physical"
1 + 1 = 3.
Not exactly. What happens in the behavioral or emotional 1 + 1 = 3 is not exactly a non-linearity, but I will call it that anyway, since the combinations resulting from the 1 + 1 grow out of a resonance mechanism associated with love. The vision of this "quasi-nonlinear" behavior of relationships came through my own experience, of course. Throughout life we learn that when two people come together in love relationships, they are two individuals who will, regardless of how close they become, keep alive from that moment on many of the individual personality and character traces they developed throughout their bachelor(ette) lives or elsewhere in other previous relationships.
The union then creates a third entity, out of resonating love, which tends to behave like a separate being, with character and personality traces of its own, since the two individuals united behave slightly or largely different to what they would when you meet them by themselves. As simple as that, and perhaps somewhat obvious, this proves that the outcome of a sum of two in a love partnership is
1 + 1 = 3.
The consequence of this is the fact that when two people spend a lot of time together and there is a strong bond between them, they have to learn how to manage three different levels of relationship that become ongoing: the one, the other and the two. Many psychologists have warned people about that they should be aware of this when caring for their own relationships, as many people enter a couple's life by either remaining excessively selfish, or overly bonded.
The truth is, the two ones in a couple should be both excessively selfish and overly bonded. And there is where the pair gives two the chance of becoming a form of art or a torn apart.
(Perhaps the idea of 1 + 1 = 3 could be extended to any type of relationship between two or more people, but the links tend to be somewhat weaker, so that a "real" third person only de facto appears systematically in relationships of love.)
Now let's extend this idea to when the physical 1 + 1 = 3, that is, when a couple has offspring or a child is adopted. What happens to the quasi-nonlinear interactions there? The expansion of the behavioral, two-people 1 + 1 = 3 theorem to the inclusion of a child leads to
1 + 1 + 1 = 7.
With the turning up of a third person, as deeply bonded to the other two through love as themselves, the interaction levels at the behavioral/emotional front increase twofold plus one. Of course, although time seems to contract when caring for a child, the new addition will keep things unchanged in the prior 1 + 1 = 3 side, but will create a new "one", two new (1 + 1)'s and a completely new invented "independent" being, the threesome (1 + 1 + 1). That is equal to seven.
In other words, there are now three individuals that need their own, hey, individuality (eg, = 3 beings), who sometimes interact altogether as the full "family" being (eg, = 1 being), and sometimes interact in doubles, such as one + two, one + three and two + three (eg, = 3 beings), thus
1 + 1 + 1 = 7.
Family relationships can become very difficult when people are not prepared to see things that way. And seeing things that way requires some preparation that goes way beyond a simple "mathematical" view of how people interact. It requires many subjective traits such as maturity and respect and independence and trust and self confidence and independence and so on so forth.
I will not elaborate on the consequences of adding a fourth member to our nonlinear family, but one can easily show with little algebra that
1 + 1 + 1 + 1 = 15.
Our sympathy, luck and love to the families of N >= 4.
(The little algebra in the derivation of the interaction levels above is the sum of N combinations without repetitions, where N is the number of people involved, so that the number of interactions will be = N elements taken 1 by 1 + N elements taken 2 by 2 + N elements taken 3 by 3 + [...] + N elements taken as a block ("N by N"). One may want to learn more about Pascal Triangles and Binomial operations in those airs.)
