Defeasible rules: corpus forms

Breakdown of real fragments: package identifier, human act name, form rating (exemplary / debatable / wrong form choice) and why.

OverviewBoundariesCorpus formsPitfalls

Law

1. ILO Convention No. 138 — contrary proviso with measured difference (exemplary)

Package intl.labour.c138 (ILO Convention No. 138, minimum age), scope and exclusions:

Arxo Law

rule WorkIsExcludable(w: Work) defeasible {
    ...
    when within_convention_reach(w);
    then excludable_work(w);
    unless hazardous_work(w) then not excludable_work(w);
}

Exemplary. The package comment records that the difference of forms is measured: a bare unless would have removed the inference and given Not established, not refuted, while what is needed here is established negation of excludability — only the contrary clause unless … then not … gives it. Absence of a fact is not its negation.

2. The 1789 Declaration — proviso in a presumption (exemplary)

Package fr.declaration.rights_1789 (Declaration of the Rights of Man and of the Citizen, France, 1789), legality:

Arxo Law

presumption Innocence(who: Person) {
    ...
    when accused(who);
    presume innocent(who);
    unless declared_guilty(who) then not innocent(who);
}

Exemplary. The same unless … then not … clause inside a presumption, not a rule: the expansion mechanics is one, the carrier is the presumption of innocence (“until declared guilty”).

3. The 1916 requisition — comment on the form choice (exemplary)

Package ru.empire.requisition_1916 (1916 requisition decree, Russian Empire), call-up: strict “would have silently swallowed” the exemptions, so the form unless … then not … was taken.

Exemplary as a documented decision: the author explicitly rejected a strict rule in favour of a defeasible one with a contrary proviso.

4. German Civil Code — proviso-refusals in property law (exemplary)

Package de.bgb.besitz_eigentum (German Civil Code, possession and ownership):

Arxo Law

unless besitzer(s, p) and bewegliche_sache(s) and vermutung_des_1006_ausgeschlossen(s) then not eigentum_vermutet(s, p);

Exemplary. A contrary proviso with a compound condition — the ownership presumption (paragraph 1006) is removed by an established refusal. Nearby in the same package — the same form for registered rights.

Custom

5. “Not caught — not a thief” proverb — proviso in a presumption (exemplary)

Package ru.dal.poslovitsy (Russian folk sayings), presumptions:

Arxo Law

presumption NePoymanNeVor(ch: Chelovek) {
    ...
    when podozrevaetsya(ch);
    presume chist_ot_tatby(ch);
    unless poyman_s_polichnym(ch) then not chist_ot_tatby(ch);
}

Exemplary. The exception-clause mechanics works outside written law: a folk presumption with the same contrary carve-out as the 1789 declaration.

Teaching packages

6. This section’s pair — bare proviso vs separate defeater (exemplary)

Package research.constructs.defeasible_unless (bare unless violation_found_last_year(e);) and package research.constructs.standalone_defeater (a separate rule ViolationRemovesExemption defeater with defeat exempt_from_planned_inspection(e);).

Exemplary as a demonstration: both forms give the same two answers (Established / Not established, not refuted); the difference is the extension point (see the defeasible-rules page, section 2).

Measurements

rule … defeasible — 6 707 in 278 packages (a general norm with exceptions); rule … defeater — 478 in 75 (an exception removing the general norm); defeat p(x) in a defeater — 606 in 78 (“the ground is gone”: suspension, seizure, moratorium); bare unless F in a rule — 584 in 77 (an article proviso “except in cases…”); unless F then not p(x) — in 26 packages (a refusal proviso); except_when — 1 in 1 package (deprecated; in corpus sources — only in comments).