The main contender for being a 6th foundation is Liberty/constraint, which includes both lifestyle liberty, and also negative liberty -- the freedom to be left alone by government. Liberals score higher on lifestyle liberty; conservatives on negative liberty.But liberty/constraint as currently suggested does not work as a foundation of human moral psychology, as morality is pre-government. Also, the proposed sixth foundation is conceived too much in specifically Western (even American) terms.
If something is another foundation of human moral psychology, its coverage will be an area of moral concern and action not covered by the current five foundations. It will also have to be moral – about general normative concerns, not merely personal ones. If it is a foundation of human moral psychology, signs of it will turn up in societies other than contemporary Western ones.
What concern with liberty gets at is personal freedom of action: the right to use our person and property, to engage in relationships, as we chose.
One form of society where outside commentators have, over the centuries, consistently commented on the freedom of the lifestyle of its members is that of the pastoralist nomads. Pastoralist nomads are typically very conceived with honour: indeed, it is a basic concern of their society. Now honour is partly about standing and status. But it is also about protecting what is yours – your person, your property, your connections. Protecting your honour is about protecting your standing as a social actor.
If you restrict someone’s freedom, you are forcing a constraining subordination on them. You are also undermining their status as a social actor. Such a restriction, even attack, on someone’s autonomy is not so far from attacking their honour. Indeed, an honour code is, in many ways, an autonomy code: a warning not to restrict someone too much. It is an insistence on personal respect, on respecting them as a social actor.
The use of ‘respect’ in the identified authority/respect moral foundation is a particular form of respect – respect for structures: hierarchy, tradition, etc. Respect as deference. The respect involved in concern for freedom and honour is respect for person, for a person as a social actor. When libertarians talk about liberty they talk about respecting people’s choices and right to choose. Which, of course, means that, if you fail to do so, you are failing to respect people. It is striking how much claims of the right to restrict people’s choices involve various sorts of trumping claims – which extend to claims of blatant disrespect but – and this is even more revealing – are often put in terms which try to deny, hide or otherwise elide any sense of disrespect. A sign that a moral minefield is attempting to be avoided.
To put it another way, libertarian concerns are how, in a modern Western society, people do the equivalent of, in pastoralist societies, talking about honour. Libertarians are, after all, typically very concerned with personal responsibility and its associated concerns, such as fair dealing and integrity. Honour and liberty rather go together – indeed, it is striking how many SF writers with military backgrounds express libertarian sentiments (and that is without considering libertarian attitudes towards weapons and self-defense).
Looking at the five identified moral foundations – harm/care, fairness/reciprocity, ingroup/loyalty, authority/respect, purity/sanctity – we can identify classic respective moral virtues to tie with them of compassion, equity, loyalty, deference and reverence. More generally: care for others, fair dealing with others, being loyal to others, respecting social structures and respecting the significance of things. There is nothing about moral standing: [about respecting people as social actors], about rights to act, to have, to connect, to do. Neither honour nor liberty is covered.
So, there is a gap in the five identified moral foundations. The gap would be covered if the sixth foundation is concern with the morality of personal standing, the morality of respect for people as social actors, for their moral autonomy. As philosopher Kwame Anthony Appiah has suggested in a recent book, honour-as-respect can be plausibly said to have had considerable power in various moral revolutions. [If morality is about grounding social cooperation, as Jonathan Haidt suggests in this Ted talk, then respect for the people as agents is surely a part of making that cooperation work, of giving people moral standing so as to make moral protections more real, more effective, more direct.]
If authority/respect is re-labelled ‘authority/deference’ (since one can, for example, respect traditions without actually following them) then the sixth moral foundation could be called ‘autonomy/respect’, cover both liberty and honour and so be neither specifically Western nor merely concerned with government.
And the morality of both libertarians and pastoralist nomads (amongst others) would be rather better covered by the identified foundations of human moral psychology.
ADDENDA This post has been somewhat [extended] to clarify and develop certain points.