Category Boundary Stability Check¶
Consistency check — instantiates Informal Fallacy Diagnosis and Repair
Holds a key term or category to one fixed meaning across the whole argument, catching definitions that drift to dodge counterexamples.
An argument can be internally tidy and still be broken because a single word means two different things by the time it is done. Category Boundary Stability Check pins the meaning of each load-bearing term or category at the point it is introduced and then verifies that the same boundary holds every time the term reappears. Its defining concern is drift: a definition that quietly expands, contracts, or is re-drawn mid-argument — most tellingly, the boundary that moves precisely when a counterexample would otherwise land, excluding the awkward case by fiat. It is not about whether the definition is a good one; it is about whether one definition is used consistently from premise to conclusion.
Example¶
A hiring panel is debating a candidate who has strong delivery but little formal computer-science background. A senior interviewer objects: "A real engineer always understands the theory underneath — this person doesn't, so they're not really an engineer." Someone points to a respected staff engineer on the team who is also self-taught and light on theory. The interviewer replies: "Well, a *real engineer of that caliber has internalized the theory even if they can't recite it."* Category Boundary Stability Check is what catches this. It inventories each use of "real engineer" as a separate unit and lays the definitions side by side: first "understands the theory," then, once the counterexample appeared, "has internalized it even without being able to state it."
Laid out that way, the defect is plain — the boundary of "real engineer" was redrawn on the fly so the counterexample could be excluded, which means the term is doing no stable work in the argument. The output is a note that the panel must fix one criterion for "engineer" before the candidate can be judged against it, not shift the line each time a case threatens the conclusion.
How it works¶
- Inventory the term's occurrences. Pull every appearance of the key term or category out of the argument as its own unit, with the sense it carries in each spot.
- Freeze the introduced boundary. Record the definition or membership criterion as stated where the term first does work, before any challenge arrives.
- Compare senses across uses. Check whether later uses match that boundary or silently widen, narrow, or re-draw it — paying special attention to redefinitions that appear right after a counterexample.
- Report the drift, not a verdict. Flag where the boundary moved and demand a single fixed criterion, leaving the truth of the claim for later steps.
Tuning parameters¶
- Boundary tightness — how precisely the definition must be pinned. A crisp criterion catches subtle drift but can reject a term that is legitimately vague and context-sensitive.
- Occurrence granularity — whether you track only the headline term or every near-synonym and pronoun that stands in for it. Finer tracking catches disguised shifts but multiplies the bookkeeping.
- Drift tolerance — how much meaning-change counts as a violation versus normal contextual variation. Zero tolerance flags honest polysemy; loose tolerance lets a genuine equivocation slide through.
- Trigger coupling — how strongly you weight redefinitions that coincide with an incoming counterexample, which are the ones most likely to be ad hoc.
When it helps, and when it misleads¶
Its strength is exposing the ad hoc redefinition, best known as No True Scotsman: the move that rescues a universal claim by re-drawing the category to expel every counterexample, so the claim can never be wrong because it no longer means anything fixed.[n1] It also catches equivocation, where a term slides between two senses across premises, and misplaced concreteness, where a category is treated as more solid than its definition supports.
Its failure mode is over-rigidity. Natural language is legitimately context-sensitive, and not every shift in a word's use is a fallacy — sometimes a term is being refined in good faith as the discussion sharpens it. Mechanically flagging every variation turns a useful clarification into an accusation and can bully a speaker into a brittle definition. The classic misuse is the mirror image: insisting that any adjustment of terms is cheating, thereby freezing a first, sloppy definition in place. The guarding discipline is to distinguish ad hoc redefinition — one that appears only to dodge a specific counterexample and buys nothing else — from principled refinement that the arguer would have accepted before the counterexample arose.
How it implements the components¶
term_and_category_stability_check— it is this component: the fixed-boundary test applied term by term across the whole argument.argument_unit_inventory— it enumerates each occurrence of the term as a discrete unit so the senses can be compared, using the inventory narrowly to isolate the definitional pieces.
It does not judge whether the inference is truth-preserving in form — formal_validity_gate belongs to Formal vs Material Error Gate; this check catches a material, semantic defect (a term's meaning drifting), not a defect in logical shape.
Related¶
- Instantiates: Informal Fallacy Diagnosis and Repair — supplies the term- and category-stability check within the wider diagnosis.
- Sibling mechanisms: Formal vs Material Error Gate · Counterexample Probe · Premise Relevance & Acceptability Test · Fallacy Label Justification Note
Editorial Notes¶
Form Classification¶
Form family: Assessment, Review & Assurance
Rationale: Holds a key term or category to one fixed meaning across the whole argument, catching definitions that drift to dodge counterexamples, making its operative form a bounded evaluation of existing evidence or work that produces a finding or disposition.
Independent corroboration: The frozen evidence defines Category Boundary Stability Check as 'Holds a key term or category to one fixed meaning across the whole argument, catching definitions that drift to dodge counterexamples', so its operative form is Assessment, Review & Assurance.
Review outcome: Independent reviewer agreement; high confidence.
Origin Attribution¶
Primary origin: Philosophy
Origin pattern: Single lineage
Present-day reach: Universal
Rationale: Informal logic identifies equivocation and No True Scotsman repairs that redefine a category after counterexamples appear.
Related originating lineages:
- Rhetoric — Argumentation analysis tracks how a speaker shifts wording or scope across the course of a dispute.
Review resolution: Philosophy is primary because the check detects ad hoc redefinition of a category after counterexamples, the logical core of No True Scotsman and equivocation diagnoses. Rhetoric and argumentation provide a genuine practical lineage for tracking shifts in contested discourse; the method has universal reach.
Review outcome: Researched adjudication after independent review; high confidence.
Sources consulted:
Notes¶
[n1] No True Scotsman, an illustration due to the philosopher Antony Flew, names the move of protecting a generalization by redefining its subject to exclude any counterexample ("no true Scotsman would do that"). This check catches it by pinning the category's boundary before challenges arrive and flagging boundaries that move to expel a case. ↩