There exists a curious parallel between the stat abilities of a D&D character and something that behaviorists refer to as the 'trait theory of leadership.' This is an historical perception (that now tends to be viewed as a fallacy) that the ability to be a leader is based upon a model of traits that are recognizable in the candidate, things like intelligence, interpersonal skills, extroversion, honesty and so on. Thomas Carlyle took a crack at codifying this at near the beginning of the Victorian Age (when every ideal was ultimately codified, whether this worked or not), so we have him to blame for the "Great Man Theory." Take a crack at it, it's a great view into the 19th century mind.
The theory has been challenged by historians since its presentation, mostly to say that history is just as adept at creating great persons as great persons are in creating history. Well, none of that is relevant to our discussion here, of a game, but it is interesting to note that when a DM takes up the argument that a character's stats determine that character's ability to lead men or promote action, the DM is diligently following in Carlyle's footsteps.
My principle of sage ability is based upon a character's decision to apply themselves and grow better, over time, measured by experience and levels gained. Thus the character who chooses to be a leader will become a better leader, regardless of their ability statistics. This, I know, is hard to relate to traditional D&D practice. A fighter with an 8 charisma becoming a leader of men? Ridiculous!
Yet we have many examples of trusted, reliable leaders who were ugly, poor of speech, who were known to have a distressing body odor, who were physically weak or overly intellectual, etcetera.
These leaders compensated for their poor qualities through honesty, hard work, luck, subordinates and generosity, patterns of behavior that have nothing whatsoever to do with charisma.
On the other hand, if any of us chooses at an early age to think continuously about leadership, to throw ourselves into politics, to learn all that we can learn about what people want, to practice debating and addressing crowds, to adapt ourselves to crowd-pleasing methods, whatever our original charisma, we will learn to be leaders. Parliment or Congress is just another Carnegie Hall.
With this in mind, we have to throw out our preconceptions about how to turn friends into allies and how to turn allies into followers. We don't really need to know which element of ability the fighter possesses that enables leadership - we can simply assume the fighter, having chosen that field, has learned to employ some method of some kind in order to get there.
We only need concern ourselves with where 'there' is.
And here the work has already been done for us. There are 8 functions of leadership, according to John Adair: defining the task, planning, briefing the team, controlling what happens, evaluating results, motivating individuals, organizing people and setting an example.
Some of these have a definite overlap with our earlier discussion of planning an expedition, so we can drop several of these - those things that have to do with organizing. For Leadership as a stand alone sage ability, we have four:
1) briefing the team describes the process of explaining matters to people on their level, so that they understand, thus creating a feeling of inclusion and camaraderie. This is in part the leader standing ahead of the army and giving a great speech before going into battle; but it is also the leader as a friendly father patiently explaining what an individual soldier has failed to understand about being a part of the team. This also includes knowing what the hold back, what not to tell, knowing that too much information of the wrong kind will undermine morale.
2) motivating people is the next step; after the underling understands, that same underling must feel a willingness to be a part of what's happening, to join in - and more than that, to join in such a manner that they're willing to take orders and believe in their hearts that these are the right orders. The leader encourages the idea that he or she is the only person for the job, not only in their own opinion but in everyone's.
3) evaluating results could be misunderstood as a part of expeditionary or strategical planning; we screwed up, how should we have done this differently? Here, however, what we mean is the leader's ability to be introspective about their own actions as well as that of their underlings, to recognize where the success or failure resulted from a failure to brief or motivate, as well as right or wrong decisions made. A leader cannot wallow in grief; at the same time, a leader must look at every part of the equation and ignore nothing.
4) setting an example is the practice of making clear in the followers mind that the leader is one of them, willing to do the same work, take part in the same struggle, have the same goals and suffer the same consequences. A great leader is not an elitist - a leader rates their own success in terms of what everyone has achieved, together, as a group, understanding that the celebration of the victory is not something accorded to the leader but something that everyone shares.
Each of these things are typically played out as an act of role-playing. We explain to the NPC what we want; we try to motivate the NPC; we question our relationship to the NPC and we quest to struggle side by side with that NPC in times of struggle (described in the last post). The trick is to fit these actions into practical, identifiable rules that the players can employ whenever they find themselves in the position of wanting to get an NPC on board with their agenda.
Obviously, I think some of the calculation has to include a sacrifice of more than just money to pay the underlings off. It is very important, I believe, that this sacrifice must be something inherent, which the player will want to embrace for the gain in power that it promotes. I don't know how possible that is; but the purpose to writing these posts is to identify the boundaries of the various fields of knowledge within the fighter's overall sage abilities. Leadership is one of those fields. Having written this and the previous post, I think I have a better handle on what is needed - though I am sorry, I have no hardened proposals to make. Those I will save for the Wiki.