Vowel Reduction

Vowel reduction collapses the vowels of unstressed syllables to a weaker, more central vowel (e.g.: schwa ə). This is characteristic of stress-timed languages: English pronounces banana as /bəˈnænə/ rather than /baˈnana/, Russian merges unstressed /o/ and /a/ (молоко /məlɐˈko/), European Portuguese reduces unstressed vowels so far they often nearly disappear, and Central Catalan collapses unstressed /a/, /e/, and /ɛ/ to [ə]. Syllable-timed languages like Spanish, standard Italian, and Japanese instead keep full vowel quality everywhere; leave reduction off for languages with that rhythm.

Natural languages vary in what unstressed vowels reduce to (Russian [ɐ], European Portuguese [ɨ], Catalan [u] for back vowels) and in which vowels reduce at all. The target and targets fields configure both aspects.

Configuration

Add a reduction section to your config JSON:

{
  "reduction": { "probability": 0.7, "target": "ə" }
}

Fields

Exactly one of target and targets must be present. If the reduction section is absent, no reduction occurs.

Targets

target is the simple form: every vowel in a reduced syllable collapses to that one vowel, as in the English-style example above.

targets gives per-vowel control. Each key is a string of one or more IPA vowels; the value is the single vowel they reduce to. Only the listed vowels reduce — everything else keeps its quality even in unstressed syllables. A vowel may appear in at most one key.

A Central Catalan–style system, where /a e ɛ/ merge to [ə] and /o ɔ/ raise to [u] while the high vowels /i u/ never reduce:

{
  "reduction": {
    "probability": 1.0,
    "targets": { "aeɛ": "ə", "oɔ": "u" }
  }
}

A Russian-style akanye, merging unstressed /o/ and /a/ into [ɐ]:

{
  "reduction": {
    "probability": 0.9,
    "targets": { "oa": "ɐ" }
  }
}

Interaction with Stress

Reduction targets whatever syllables are left unstressed by stress assignment, so which syllables are eligible is determined by the stress configuration:

• Syllables carrying primary stress never reduce. This includes monosyllabic words, which always receive primary stress (unless the strategy is none).
• A class with "stress": "none" has every syllable eligible, so the word can reduce entirely.
• With "secondary": true, alternating syllables carry secondary stress and are also protected, halving the eligible syllables in longer words.

Because of this dependency, a sketch with a reduction section but no stress configuration at all (no top-level stress and no per-class "stress" fields) is rejected as a validation error. Without stress, every vowel is a candidate for reduction, which leads to an undirected mush of whatever your target is. If you still want this, you can explicitly write "stress": "none" at the top-level or per-class.

Behavior

• Reduction runs after stress assignment, so it depends on the final stress marking of each word.
• Only fully unstressed syllables are eligible. Syllables with primary or secondary stress never reduce. Secondary stress protects vowel quality, as it does in English (compare the final syllables of ˈal.pha.ˌbet and ˈtrum.pet).
• Word classes with "stress": "none" have every syllable unstressed, so function-word classes (determiners, pronouns, prepositions) reduce throughout — giving the “the → ðə, of → əv” effect.
• The whole vocalic nucleus reduces: diacritics on the vowel are dropped, and a diphthong collapses to a single vowel. With targets, a diphthong is keyed by its first component (so with "aeɛ": "ə", /ai/ collapses to [ə] but /ui/ is untouched). Consonants in the onset and coda are untouched.
• Reduction applies to a word’s lexicon entry when the vocabulary is pre-generated, so a reduced word form is stable across a session.
• A reduction target may appear in output even if it is not in the configured vowel inventory; targets are outcomes of reduction, not inventory phonemes.