A formal method that augments syntactic formulas with explicit labels (such as worlds, states, resources, or proof annotations) that carry semantic information and guide the application of syntactic inference rules.

Principle

Attach minimal semantic annotations as labels to syntactic objects so that rule application and proof composition become local, syntax-directed operations governed by label-manipulation rules.

Demonstration

In modal logic, each formula is paired with a world label w and rules permute or relate labels (wRv) to simulate accessibility; a sequent like w:A, wRv ⊢ v:B makes the semantics of □ and ◇ explicit in the proof steps.

Misapplication

Treating labels only as cosmetic tags and failing to enforce label constraints leads to unsound proofs where semantic relations (for example accessibility or resource consumption) are ignored.

Consequence

Correctly used, labelled deduction yields proof systems that are closer to semantic models, enable localized rule application, permit modular extensions for new modalities or resources, and often simplify cut-elimination or countermodel extraction.

Reversal

The reversal is pure syntactic deduction without labels, where rules must implicitly track semantic conditions globally; this can make some systems less modular and increase nondeterminism in proof search.

Boundary

Applies to logics where semantic structure can be encoded as finite label algebra or relational constraints; it excludes approaches that require full semantic evaluation at each step (e.g., heavy model checking) rather than symbolic label manipulation.

Semantic Tension

Tension exists between label-heavy systems that expose semantic detail in proofs and labelled calculi that keep labels minimal to preserve syntactic elegance; more labels improve semantic fidelity but increase proof complexity.

Synthesis

Labelled deduction is a method that embeds semantic bookkeeping into syntax via labels, trading global semantic appeals for local, rule-driven label transformations that make reasoning about modalities, resources, or states explicit and modular.