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Query multi-character consensus

When a scene has multiple characters with different value priorities, the natural question becomes: "which proposals does the whole council agree on?" The MultiAudience API answers this — it intersects acceptance across every character's audience.

Learning objective: given a ValueBasedFramework and two audiences (e.g., for a 2-officer council), compute the unanimously-accepted argument set in 5 lines of code.

Prerequisites​

The use case​

Scenes with multiple deliberators — councils, juries, cabinets — often have characters who hold different value priorities. Some proposals will land regardless of who you ask (universal consensus); others depend on whose audience you adopt. MultiAudience::common_grounded answers the universal-consensus question.

Step 1: Build per-character audiences​

use argumentation_values::{Audience, Value};

// Aleric values defending the realm above all.
let aleric = Audience::total([
    Value::new("duty"),
    Value::new("survival"),
    Value::new("comfort"),
]);

// Maren prioritises survival.
let maren = Audience::total([
    Value::new("survival"),
    Value::new("duty"),
    Value::new("comfort"),
]);

let council = [aleric, maren];

Step 2: Construct the MultiAudience query​

use argumentation_values::MultiAudience;

let multi = MultiAudience::new(&council);

Step 3: Query consensus​

let consensus = multi.common_grounded(&vaf)?;

if consensus.is_empty() {
    println!("The council cannot agree on anything universally.");
} else {
    println!("Universally accepted: {:?}", consensus);
}

common_grounded returns the set of arguments grounded under every audience in the slice — the strictest form of consensus.

Step 4: For weaker consensus, use common_credulous​

let weak_consensus = multi.common_credulous(&vaf)?;

common_credulous returns arguments that are credulously accepted (i.e., in some preferred extension) under every audience — a less restrictive answer. Use this when you want "no character could rule this out completely" rather than "every character would defend this."

Worked example: 4-officer council​

use argumentation_values::{
    Audience, MultiAudience, Value, ValueAssignment, ValueBasedFramework,
};
use argumentation::ArgumentationFramework;

// Build the siege-council framework.
let mut base = ArgumentationFramework::new();
for arg in ["fortify", "abandon", "sortie", "evacuate"] {
    base.add_argument(arg);
}
base.add_attack(&"fortify", &"abandon")?;
base.add_attack(&"abandon", &"fortify")?;
base.add_attack(&"sortie", &"abandon")?;

let mut values = ValueAssignment::new();
values.promote("fortify", Value::new("duty"));
values.promote("abandon", Value::new("survival"));
values.promote("sortie", Value::new("victory"));
values.promote("evacuate", Value::new("survival"));

let vaf = ValueBasedFramework::new(base, values);

// Each officer has their own audience.
let aleric = Audience::total([Value::new("duty"), Value::new("victory"), Value::new("survival")]);
let maren  = Audience::total([Value::new("survival"), Value::new("duty"), Value::new("victory")]);
let drust  = Audience::total([Value::new("victory"), Value::new("duty"), Value::new("survival")]);
let liss   = Audience::total([Value::new("survival"), Value::new("victory"), Value::new("duty")]);

let council = [aleric, maren, drust, liss];
let multi = MultiAudience::new(&council);

let consensus = multi.common_grounded(&vaf)?;
println!("Council consensus: {:?}", consensus);

Empty audience set​

MultiAudience::new(&[]) is a valid construction — empty universal quantifier means every argument is trivially in the consensus set:

let no_audiences = MultiAudience::new(&[]);
let everything = no_audiences.common_grounded(&vaf)?;
assert_eq!(everything.len(), vaf.base().len());

This is rarely useful directly, but it lets the API stay total without special-casing.

Cost​

Each common_grounded call costs k × O(grounded extension) where k is the audience count. Each common_credulous call costs k × O(preferred extensions) — preferred is exponential in the worst case but tractable for narrative-scale frameworks (≤ 22 args, the upstream ENUMERATION_LIMIT).

For very large councils (10+ characters), prefer common_grounded over common_credulous — the cost gap widens with audience count.

When NOT to use this​

  • Single-character scenes. Use vaf.grounded_for(&audience) directly.
  • Asymmetric votes (e.g., the king's audience counts double). MultiAudience is symmetric — model weighted voting at a higher layer.
  • Probabilistic acceptance. Not a feature. See open areas for the probabilistic AF roadmap.