The GUMSHOE system focuses primarily on investigation and by default assumes that moments of interpersonal conflict will be handled through roleplaying. As such it lacks an equivalent of the Persuasion/Rebuff system that lies, for example, at the heart of the Dying Earth Roleplaying Game. However, if you’re seeking a more mechanically robust way to adjudicate the outcomes of arguments, negotiations, debates and seductions, there are plenty of options to choose from.
When contemplating a new rule or technique, the GUMSHOE way is to look at the source material, see what techniques it typically uses, and find the simplest possible means of implementing it, consistent with the rest of the system.
Scenes of interpersonal conflict in mystery novels and TV procedurals are usually handled as in any other dramatic genre, although usually in a more compressed and decisive way.
In resolving a character conflict in fiction, an author ideally finds a plausible and organic way to portray a plot development he deems to be necessary to his story. This necessity may arise from, among other reasons, a desire to illuminate character, jolt the audience, or move a story toward its inevitable conclusion. In a roleplaying game, the outcome is not preplanned. The PC may or may not bring about a plot turn that moves the group toward a successful resolution. Two elements must be in place: the player has to devise a believable plan, and then the character must have the wherewithal, and perhaps luck, to implement it.
In the case of interpersonal conflicts, what is plausible and organic depends on the motivations of the character being persuaded. What the GM does determine in advance are the motivations and intentions of the NPC with whom the PC enters into the verbal exchange.
The motivation is what the character wants. This goal can be specific or general. The more proactive the NPC, the more specific the goal will be.
Specific goals might include:
General motivations are more inchoate and psychological:
If you want to get fancy about it, a specific goal might be rooted in a general goal. Ernest Combs may want to gain the Botticelli Secret to destroy a father figure, his hated former mentor Elias Thwaite.
Greater complexity can be added in the form of multiple or even contradictory motivations. Mrs. Spooner may want to rent the downstairs apartment, earn the flirtatious attention of handsome men, while still proving that she is a respectable citizen.
GUMSHOE is player-facing, meaning that it treats PCs and NPCs differently. PCs are the protagonists, who act. NPCs exist only in relation to them and tend not to make rolls on their own. So if an NPC sneaks up on a PC, the action is resolved not by the GM rolling for the NPC, but by the player rolling against his Surveillance or Sense Trouble ability to see if he notices.
The implication of this principle in interpersonal conflicts is that the PCs are not open to being persuaded or bamboozled, as they are in Dying Earth, by a rules resolution. Only when the players decide it’s in character to be deceived or inveigled do they act against their better judgment. This is in keeping with the procedural genre, which can be described as a romance of competence.
In a scene of personal conflict, then, a PC must overcome the NPC’s resistance, rooted in his motivation, and pivot him so that he becomes open to an action he is at first unwilling to embark upon.
We already have this in the system with Interpersonal Investigative abilities. NPCs are often resistant to giving out information until the players figure out what ability (Bargain, Flattery, Seduction, Streetwise, et al) can best be used to overcome their objections.
Interpersonal abilities can also be used to overcome resistance in other areas. To do so, the player must specify a tactic. The tactic is an approach, offer, or argument made to overcome another person’s resistance. This might or might not cite an interpersonal ability. Let’s say that Ernest Combs has taken a hostage, who the PC wants to him to release.
If the player comes up with a tactic, which, given Combs’ motivations, will make his capitulation seem plausible, the conflict is resolved in his favor:
Sometimes non-Interpersonal abilities might apply:
A prepared GM can designate one or more possible successful tactics ahead of time, but should also be ready to accept unexpected yet equally plausible suggestions from the players.
This system not only emulates the source literature, but gives investigators a reason to learn more about the NPCs in any scenario—you never know when you’ll need to persuade them of something later on in the story.
The extent to which ability ratings influence outcomes is a matter of taste.
The minimalist approach is the triggered result—here, resistance is overcome simply by citing an ability plus a plausible tactic (or even a plausible tactic to which no ability applies.) The triggered result is congruent with the clue-gathering mechanic.
You may wish to have players pay a toll to succeed in interactions which yield non-informational advantages. In this case, require an interpersonal spend. The player succeeds after paying 1 or 2 points from the cited ability. Combs releases the hostage on a 2-point spend of Intimidation, Flattery, or Bargain, depending on which tactic the player selects. Add complexity by assessing different spend levels reflecting the relative aptness of the various tactics: the Bargain might cost 1 point, whereas the Flattery, which is a bit of a stretch given the investigator’s previously expressed antipathy for Combs, costs 3.
Finally, you might prefer, even with a plausible tactic, an uncertain or chancy outcome. In an interpersonal contest, the GM assigns a Difficulty to the persuasion attempt, based on the aptness of the tactic. A Difficulty of 4 is standard; higher than that represents an especially tough challenge. The player can add to the die result by spending points from the relevant investigative ability, gaining a +2 result bonus for each ability point spent. This approach is in keeping with traditional roleplaying approaches to the problem, and introduces an element of suspense, and, therefore, uncertainty. On the downside, it is less like the source material, and therefore less GUMSHOE-y.
You may always find that one of the three techniques—the triggered result, interpersonal spend, or interpersonal contest—is best suited to your style of play. However, you may find that certain situations call for the automatic certitude of the triggered result, while others cry out for the plot-branching potential of the interpersonal contest. Creators of fiction vary their techniques to achieve a range of effects, and GMs should do likewise.