{"id":"GRM-012","name":"A/an follows sound","domain":"grammar","layer":"phrase","strength":"hard_constraint","human_logic":"IF an indefinite article precedes a singular noun phrase, THEN choose A before a consonant sound OR AN before a vowel sound ELSE retain.","when":{"all":[{"path":"determiner.type","operator":"eq","value":"indefinite_article"},{"path":"noun_phrase.initial_sound","operator":"exists"}]},"then":[{"action":"select","target":"determiner.form","by":"noun_phrase.initial_sound","map":{"consonant":"a","vowel":"an"}}],"else":[{"action":"retain","target":"current_text","reason":"No triggering condition is present."}],"unless":[],"because":"The choice follows pronunciation rather than spelling.","diagnostics":[],"examples":{},"source_ids":["BK-002","BK-004","BK-010"],"laka":{"smallest_sufficient_intervention":true,"primary_axes":["scope","depth","magnitude","reversibility"]},"requires_facts":["determiner.type","noun_phrase.initial_sound"],"tests":[],"sources":[{"id":"BK-002","title":"The Blue Book of Grammar and Punctuation","creator":"Jane Straus; Lester Kaufman","domain":"grammar_reference","type":"Book","note":"Accessible grammar, punctuation, examples, and exercises.","url":null},{"id":"BK-004","title":"English Grammar in Use","creator":"Raymond Murphy","domain":"learner_grammar","type":"Book","note":"Self-study explanations and practice for core English grammar.","url":null},{"id":"BK-010","title":"Practical English Usage","creator":"Michael Swan","domain":"usage_reference","type":"Book","note":"Advanced grammar and usage reference for learners and teachers.","url":null}],"defined_in":{"file":"07-core-grammar-rules.json","title":"Core Grammar Rules","slug":"core-grammar-rules"}}