diff --git a/src/subsumption.js b/src/subsumption.js
new file mode 100644
index 0000000..8fb52bb
--- /dev/null
+++ b/src/subsumption.js
@@ -0,0 +1,155 @@
+/**
+ * @import { NormalizedOutput, InstanceOutput } from "./index.d.ts"
+ */
+
+/**
+ * @typedef {{ loc: string, errors: NormalizedOutput[] | null }} FailedCondition
+ */
+
+/** @type {(altA: NormalizedOutput, altB: NormalizedOutput, getValue: (keywordLocation: string) => any) => boolean} */
+export const isSubsumed = (altA, altB, getValue) => {
+  for (const instLoc in altA) {
+    if (!(instLoc in altB)) {
+      return false;
+    }
+
+    const failedA = getFailedKeywords(altA[instLoc]);
+    const failedB = getFailedKeywords(altB[instLoc]);
+
+    for (const uriA in failedA) {
+      for (const itemA of failedA[uriA]) {
+        if (failedB[uriA] && failedB[uriA].some(/** @type {FailedCondition} */ (b) => b.loc === itemA.loc)) {
+          continue;
+        }
+
+        const valA = getValue(itemA.loc);
+        let subsumed = false;
+
+        if (uriA === "https://json-schema.org/keyword/type") {
+          subsumed = doesTypeSubsume(valA, failedB, getValue);
+        } else if (uriA === "https://json-schema.org/keyword/enum") {
+          subsumed = doesEnumSubsume(valA, failedB, getValue);
+        } else if (uriA === "https://json-schema.org/keyword/maxLength" || uriA === "https://json-schema.org/keyword/maximum" || uriA === "https://json-schema.org/keyword/maxItems" || uriA === "https://json-schema.org/keyword/maxProperties" || uriA === "https://json-schema.org/keyword/maxContains") {
+          subsumed = doesMaxBoundSubsume(uriA, valA, failedB, getValue);
+        } else if (uriA === "https://json-schema.org/keyword/minLength" || uriA === "https://json-schema.org/keyword/minimum" || uriA === "https://json-schema.org/keyword/minItems" || uriA === "https://json-schema.org/keyword/minProperties" || uriA === "https://json-schema.org/keyword/minContains") {
+          subsumed = doesMinBoundSubsume(uriA, valA, failedB, getValue);
+        } else if (uriA === "https://json-schema.org/keyword/anyOf" || uriA === "https://json-schema.org/keyword/oneOf") {
+          subsumed = doesAnyOfSubsume(itemA, altB, getValue);
+        }
+
+        if (!subsumed) {
+          return false;
+        }
+      }
+    }
+  }
+
+  return true;
+};
+
+/** @type {(valA: any, failedB: Record<string, FailedCondition[]>, getValue: (keywordLocation: string) => any) => boolean} */
+const doesTypeSubsume = (valA, failedB, getValue) => {
+  const typeA = Array.isArray(valA) ? valA : [valA];
+
+  if (failedB["https://json-schema.org/keyword/type"]) {
+    for (const itemB of failedB["https://json-schema.org/keyword/type"]) {
+      const typeB = Array.isArray(getValue(itemB.loc)) ? getValue(itemB.loc) : [getValue(itemB.loc)];
+      if (typeB.every(/** @param {any} t */ (t) => typeA.includes(t))) {
+        return true;
+      }
+    }
+  }
+
+  if (typeA.includes("string") && (failedB["https://json-schema.org/keyword/minLength"] || failedB["https://json-schema.org/keyword/maxLength"] || failedB["https://json-schema.org/keyword/pattern"] || failedB["https://json-schema.org/keyword/format"])) {
+    return true;
+  }
+  if ((typeA.includes("number") || typeA.includes("integer")) && (failedB["https://json-schema.org/keyword/minimum"] || failedB["https://json-schema.org/keyword/maximum"] || failedB["https://json-schema.org/keyword/exclusiveMinimum"] || failedB["https://json-schema.org/keyword/exclusiveMaximum"] || failedB["https://json-schema.org/keyword/multipleOf"])) {
+    return true;
+  }
+  if (typeA.includes("object") && (failedB["https://json-schema.org/keyword/properties"] || failedB["https://json-schema.org/keyword/required"] || failedB["https://json-schema.org/keyword/minProperties"] || failedB["https://json-schema.org/keyword/maxProperties"] || failedB["https://json-schema.org/keyword/patternProperties"] || failedB["https://json-schema.org/keyword/additionalProperties"] || failedB["https://json-schema.org/keyword/dependentRequired"])) {
+    return true;
+  }
+  if (typeA.includes("array") && (failedB["https://json-schema.org/keyword/items"] || failedB["https://json-schema.org/keyword/minItems"] || failedB["https://json-schema.org/keyword/maxItems"] || failedB["https://json-schema.org/keyword/minContains"] || failedB["https://json-schema.org/keyword/maxContains"] || failedB["https://json-schema.org/keyword/contains"] || failedB["https://json-schema.org/keyword/prefixItems"] || failedB["https://json-schema.org/keyword/additionalItems"] || failedB["https://json-schema.org/keyword/unevaluatedItems"] || failedB["https://json-schema.org/keyword/uniqueItems"])) {
+    return true;
+  }
+
+  return false;
+};
+
+/** @type {(valA: any, failedB: Record<string, FailedCondition[]>, getValue: (keywordLocation: string) => any) => boolean} */
+const doesEnumSubsume = (valA, failedB, getValue) => {
+  const enumA = valA.map(/** @param {any} v */ (v) => JSON.stringify(v));
+
+  if (failedB["https://json-schema.org/keyword/enum"]) {
+    for (const itemB of failedB["https://json-schema.org/keyword/enum"]) {
+      const enumB = getValue(itemB.loc).map(/** @param {any} v */ (v) => JSON.stringify(v));
+      if (enumB.every(/** @param {any} v */ (v) => enumA.includes(v))) {
+        return true;
+      }
+    }
+  }
+
+  if (failedB["https://json-schema.org/keyword/const"]) {
+    for (const itemB of failedB["https://json-schema.org/keyword/const"]) {
+      if (enumA.includes(JSON.stringify(getValue(itemB.loc)))) {
+        return true;
+      }
+    }
+  }
+  return false;
+};
+
+/** @type {(uriA: string, valA: number, failedB: Record<string, FailedCondition[]>, getValue: (keywordLocation: string) => any) => boolean} */
+const doesMaxBoundSubsume = (uriA, valA, failedB, getValue) => {
+  if (failedB[uriA]) {
+    for (const itemB of failedB[uriA]) {
+      if (valA >= getValue(itemB.loc)) {
+        return true;
+      }
+    }
+  }
+  return false;
+};
+
+/** @type {(uriA: string, valA: number, failedB: Record<string, FailedCondition[]>, getValue: (keywordLocation: string) => any) => boolean} */
+const doesMinBoundSubsume = (uriA, valA, failedB, getValue) => {
+  if (failedB[uriA]) {
+    for (const itemB of failedB[uriA]) {
+      if (valA <= getValue(itemB.loc)) {
+        return true;
+      }
+    }
+  }
+  return false;
+};
+
+/** @type {(itemA: FailedCondition, altB: NormalizedOutput, getValue: (keywordLocation: string) => any) => boolean} */
+const doesAnyOfSubsume = (itemA, altB, getValue) => {
+  if (!itemA.errors) {
+    return false;
+  }
+  for (const nestedAltA of itemA.errors) {
+    if (isSubsumed(nestedAltA, altB, getValue)) {
+      return true;
+    }
+  }
+  return false;
+};
+
+/** @type {(output: InstanceOutput) => Record<string, FailedCondition[]>} */
+const getFailedKeywords = (output) => {
+  /** @type {Record<string, FailedCondition[]>} */
+  const failed = {};
+  for (const uri in output) {
+    for (const loc in output[uri]) {
+      const val = output[uri][loc];
+      if (val === false || Array.isArray(val)) {
+        if (!failed[uri]) {
+          failed[uri] = [];
+        }
+        failed[uri].push({ loc, errors: Array.isArray(val) ? val : null });
+      }
+    }
+  }
+  return failed;
+};
diff --git a/src/subsumption.test.js b/src/subsumption.test.js
new file mode 100644
index 0000000..2f74c50
--- /dev/null
+++ b/src/subsumption.test.js
@@ -0,0 +1,175 @@
+/**
+ * @import { NormalizedOutput } from "./index.js";
+ */
+import { describe, test, expect } from "vitest";
+import { isSubsumed } from "./subsumption.js";
+
+describe("Algebraic Error Subsumption", () => {
+  test("type string subsumes type string + minLength", () => {
+    /** @type NormalizedOutput */
+    const altA = {
+      "": {
+        "https://json-schema.org/keyword/type": { "/type": false }
+      }
+    };
+    /** @type NormalizedOutput */
+    const altB = {
+      "": {
+        "https://json-schema.org/keyword/type": { "/type": false },
+        "https://json-schema.org/keyword/minLength": { "/minLength": false }
+      }
+    };
+
+    /** @type {(loc: string) => any} */
+    const getValue = (loc) => {
+      if (loc === "/type") {
+        return "string";
+      }
+      if (loc === "/minLength") {
+        return 3;
+      }
+    };
+
+    expect(isSubsumed(altA, altB, getValue)).toBe(true);
+    expect(isSubsumed(altB, altA, getValue)).toBe(false);
+  });
+
+  test("broader type array subsumes strict type", () => {
+    /** @type NormalizedOutput */
+    const altA = {
+      "": {
+        "https://json-schema.org/keyword/type": { "/type": false }
+      }
+    };
+    /** @type NormalizedOutput */
+    const altB = {
+      "": {
+        "https://json-schema.org/keyword/type": { "/type_strict": false }
+      }
+    };
+
+    /** @type {(loc: string) => any} */
+    const getValue = (loc) => {
+      if (loc === "/type") {
+        return ["string", "number"];
+      }
+      if (loc === "/type_strict") {
+        return "string";
+      }
+    };
+
+    expect(isSubsumed(altA, altB, getValue)).toBe(true);
+    expect(isSubsumed(altB, altA, getValue)).toBe(false);
+  });
+
+  test("enum subsumes narrower enum", () => {
+    /** @type NormalizedOutput */
+    const altA = {
+      "": {
+        "https://json-schema.org/keyword/enum": { "/enum_broad": false }
+      }
+    };
+    /** @type NormalizedOutput */
+    const altB = {
+      "": {
+        "https://json-schema.org/keyword/enum": { "/enum_strict": false }
+      }
+    };
+
+    /** @type {(loc: string) => any} */
+    const getValue = (loc) => {
+      if (loc === "/enum_broad") {
+        return ["a", "b"];
+      }
+      if (loc === "/enum_strict") {
+        return ["a"];
+      }
+    };
+
+    expect(isSubsumed(altA, altB, getValue)).toBe(true);
+    expect(isSubsumed(altB, altA, getValue)).toBe(false);
+  });
+
+  test("enum subsumes const", () => {
+    /** @type NormalizedOutput */
+    const altA = {
+      "": {
+        "https://json-schema.org/keyword/enum": { "/enum_broad": false }
+      }
+    };
+    /** @type NormalizedOutput */
+    const altB = {
+      "": {
+        "https://json-schema.org/keyword/const": { "/const_a": false }
+      }
+    };
+
+    /** @type {(loc: string) => any} */
+    const getValue = (loc) => {
+      if (loc === "/enum_broad") {
+        return ["a", "b"];
+      }
+      if (loc === "/const_a") {
+        return "a";
+      }
+    };
+
+    expect(isSubsumed(altA, altB, getValue)).toBe(true);
+    expect(isSubsumed(altB, altA, getValue)).toBe(false);
+  });
+
+  test("nested objects", () => {
+    /** @type NormalizedOutput */
+    const altA = {
+      "/foo": {
+        "https://json-schema.org/keyword/type": { "/properties/foo/type": false }
+      }
+    };
+    /** @type NormalizedOutput */
+    const altB = {
+      "/foo": {
+        "https://json-schema.org/keyword/type": { "/properties/foo/type": false },
+        "https://json-schema.org/keyword/minLength": { "/properties/foo/minLength": false }
+      }
+    };
+
+    /** @type {(loc: string) => any} */
+    const getValue = (loc) => {
+      if (loc === "/properties/foo/type") {
+        return "string";
+      }
+      if (loc === "/properties/foo/minLength") {
+        return 3;
+      }
+    };
+
+    expect(isSubsumed(altA, altB, getValue)).toBe(true);
+    expect(isSubsumed(altB, altA, getValue)).toBe(false);
+  });
+
+  test("nested applicators subsume child const", () => {
+    /** @type NormalizedOutput */
+    const altA = {
+      "": {
+        "https://json-schema.org/keyword/anyOf": {
+          "/anyOf": [
+            { "": { "https://json-schema.org/keyword/const": { "/anyOf/0/const": false } } },
+            { "": { "https://json-schema.org/keyword/const": { "/anyOf/1/const": false } } }
+          ]
+        }
+      }
+    };
+
+    /** @type NormalizedOutput */
+    const altB = {
+      "": {
+        "https://json-schema.org/keyword/const": { "/anyOf/0/const": false }
+      }
+    };
+
+    const getValue = () => null;
+
+    expect(isSubsumed(altA, altB, getValue)).toBe(true);
+    expect(isSubsumed(altB, altA, getValue)).toBe(false);
+  });
+});