I want to explore a curious trend in interpersonal relationships. For the purposes of this post, I will restrict myself to four types (stages) of relationships: strangers, acquaintances, friends, and significant others. Not all relationships have all four stages, and a lot of subtleties are left out, but it illustrates a point that applies to the missing pieces as well.
What does it mean for two people to be acquaintances instead of strangers? The status of a relationship is, of course, a Color: there's nothing in the physical composition of two people which classifies them as acquaintances. This particular Color is determined by whether the two people have been introduced before or otherwise know each other. Behaviorally, however, there are observable differences: acquaintances will say hi if they pass each other in the hallway; they might make ask about each other's family, and so on. Importantly, these are behaviors that would be considered weird for strangers perform, and it would be bordering on inappropriate to ask about a stranger's family. We might say, then, that acquaintances have (implicitly) given each other permission to perform these actions.
More generally, there are four types of attributes I want to examine in social relationships: permissions, freedoms, obligations, and restrictions. Permissions, as demonstrated above, are behaviors that it is now acceptable to do (say, as an acquaintance). Freedoms are, in some sense, the opposite: it is something you were doing before, but is now acceptable to not do; an example might be the need to avoid meeting someone's gaze. On the other hand, obligations are things that you are now required to do (for example, a nod of the head to an acquaintance), while restrictions are things that you are not required to not do (for example, yell at an acquaintance for no reason). These describe changes in how two people relate to each other, as they progress through the stages, from strangers to acquaintances to friends to significant others. The exact behaviors differ from relationship to relationship, but these examples seem to be relatively universal, and in either case, the general idea survives.
As you might have noticed from the description, these concepts are symmetric:
That is, permissions are about what a person may do, freedoms are about what a person may not-do, and so on. There is a duality between the do's and the don't's, since one can always be framed as the inverse of the other. To take an example from above, the freedom from having to avert your gaze can also be framed as the permission to match someone's gaze. This relates to the philosophical idea of action, but since that's outside the scope of what I want to talk about here, I will keep all four terms for clarity.
Given this scale, how do the four stages of interpersonal relationships differ? Examples of behavior for acquaintances have already been given, so I will move on to behavior for friends. As friends, the permissions granted are increased: friends are allowed to insult each other, which acquaintances may misinterpret or take offense by. That in itself is also a freedom, from worry about easily offending someone. The obligations of friendship are harder to define; some people would say that you are obligated to provide emotional support, although I feel this is more elective than a requirement, especially for friendships among men. I can think of no additional restrictions on friends beyond those of between acquaintances either.
If we review the trends at this point, it would seem that the permissions and freedoms grow as a relationship deepens, while the obligations and restrictions remain minimal; even the ones that do exist are mostly the ones expected of polite human beings in general, not ones that apply specifically between friends. We might expect that this trend continue to hold when friends become significant others; we would also be wrong.
When people begin dating, the permissions (eg. sexual contact) and freedoms (eg. needing to present a particular image) continue to increase, but somehow, a host of obligations and restrictions also come into play. The most prominent of these may be the restriction of sexual fidelity, or otherwise known as "not cheating". (I must again emphasize that these behaviors are not universal, although it seems to be accurate for the majority.) This restriction is particularly notable, because its scope is not between the two people in the relationship, but between them and everyone else. Translated into the friendship context, it would be the equivalent of requiring your friends not to be friends with someone else; while these kinds of people do exist, they are usually not the kind of people we want to be friends with in the first place. There are obligations too; there is a definite expectation to provide emotional (as well as financial) support, as well as the expectation that the relationship will be somewhat long-term, especially for marriages.
That romantic relationships have obligations and restrictions that friendships don't is not a bad thing a priori. Evolutionary psychology suggests that the difference in biology between men and women has led to sexual jealousy, and obligations and restrictions may be a way of making people feel secure, that was eventually got adopted into the societal narrative of relationships. Since obligations and restrictions are often desired by both parties in a relationship, man people can in accordance with them voluntarily, without questioning whether they want these obligations or not. Given how ingrained these expectations are in society, I suspect that most people are not even aware that alternatives exist.
Well known or not, the are models where the obligations and restrictions are more lax. The most common is the family of practices which do not require sexual fidelity, such as polyamory and open relationships. Although less restrictive than mono-amory, they are not necessarily restriction free; elements of exclusivity remain, as there are often stipulations about whether and when one partner can have sex with someone outside the relationships, as well as limits on the amount of emotional investment allowed. Friend-with-benefit and no-strings-attached type relationships have similar restrictions on emotional investment.
Alternatives to other aspects of normal relationships are harder to find. I don't know if a word exists for romantic relationships where partners do not provide emotional support, even though this is almost the default among friendships. The lack of expectation for the relationship to last seems to be equally rare, although again common between friends. At least, I have not heard of people celebrating any anniversaries of friendships (outside of the friendship forming over a particular event), while the time frame for celebrations for couples seem to shrink by the ~~year~~ month. These celebrations do not directly suggest that the partners want the relationship to last, but it does suggest that many future celebrations are expected.
(EDIT: The above two paragraphs are not being fair to polyamorous relationships; many in the community also question using length as a metric for relationships. See the comments for details.)
If we remove obligations and restrictions, what is left are relationships based on permissions and freedoms - the permission to cuddle and have sex, the permission to have long conversations about any topic, the permission to access your thoughts and feelings; the freedom from all the other pressures that society normally exerts on you, the freedom to truly be yourself, the freedom to do whatever you want.
I'm not sure whether such relationships are possible, and if they are, whether there is a reason to prefer them over traditional relationships with obligations and restrictions. From the single conversation I've had on this topic, it's unclear to me whether the need to impose these obligations on others can be deliberately reduced; if they can't, that restriction-free relationships (or, if you prefer to be positive, permission-based relationships) remain a thought experiment. Regardless of whether it can be made into reality, I must admit that such a relationship holds a lot of appeal to me, as I would not be bound by anyone, and others would be similarly not bound to me. Such a conception of relationships would also bring it in line with acquaintanceships and friendships, while blurring the line between all three. I myself have never been clear on the boundaries anyway, but that would be the topic of another post.