Chapter 19. Phonology Deep Dive#

The Lojban Sound System#

Lojban was designed to be pronounceable by speakers of all major world languages. Its phonology is conservative: only sounds that appear across many different language families were chosen.

If English is your first language#

Spelling and sound line up, but English habits mislead unless you override them:

Diphthongs (ai ei oi au) are one syllable each — a glide ending toward /j/ or /w/, not two separate vowel letters in speech. Rough parallels: kight, day, boy, cow (accents differ; aim for a single moving vowel, not “ah-ee” as two beats).

Punctuation is phonemic: . marks a real pause (often glottal stop) before a vowel-initial word; , inside a word only disambiguates syllables (Special Characters below). There are no “silent letters” in ordinary Lojban words.

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Vowels#

Lojban has six vowels:

y is special: it's the "buffer vowel" used in lujvo and to resolve consonant clusters. It never carries stress, cannot start a word, and doesn't count when determining consonant clusters in morphology.

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Consonants#

Key pronunciation notes:

• c = /ʃ/ (English sh) — never /k/ or /s/
• j = /ʒ/ — the middle sound of measure
• x = /x/ — the back-of-throat sound, not /ks/ or /gz/
• g = always hard /g/ — never /dʒ/ as in English gem

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Voiced / Unvoiced Pairs#

Lojban consonants come in voiced/unvoiced pairs:

This pairing matters for consonant cluster rules: a voiced consonant cannot be directly adjacent to an unvoiced one (with a few exceptions: sf, zv, jv, lv, etc.) without a separating vowel.

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Special Characters#

Apostrophe (') — represents /h/ (a voiceless glottal fricative, like English h). It always appears between vowels and creates a brief breathing gap:

ta'a = /taˈha/ (roughly) — two syllables with h between ki'a = /kiˈha/ — exclamation of puzzlement

The apostrophe is required in writing wherever this /h/ sound appears. You cannot omit it.

Period (.) — represents a full stop or pause. Required before any word beginning with a vowel:

.abu (the letter a) — pause before the vowel .i — sentence separator: pause then /i/ la .alis. — pause before and after the name Alice

The period is a genuine phonological element — a glottal stop or short silence. In careful speech, every word-initial vowel is preceded by a pause.

Comma (,) — used only within words to mark a syllable break that might otherwise be ambiguous. It has no pronunciation; it is a written-only aid to parsing:

.ei,u — two separate vowels (not the diphthong ei + u), or to mark that ei and u are in separate syllables

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Diphthongs#

A diphthong is a two-vowel sequence pronounced as a single syllable (no separating consonant or apostrophe):

Four true diphthongs (falling — the first vowel is more prominent):

• ai /aj/ — like English kite
• ei /ej/ — like English day
• oi /oj/ — like English boy
• au /aw/ — like English cow

These are used in attitudinals (.ui .oi .ai .ei) and cmavo.

Vowel pairs with apostrophe are not diphthongs — the /h/ separates them into two syllables:

u'i = /uhi/ — two syllables, not a diphthong

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Stress Rules#

Lojban stress is penultimate (second-to-last syllable) for all brivla, and conventional (usually first syllable) for cmavo:

For brivla:

KLA-ma (klama) PRE-nu (prenu) BLA-nu (blanu) mel-BI — no, wrong: MEL-bi (melbi)

The stress always falls on the vowel of the second-to-last syllable. The y vowel and apostrophe are ignored when counting syllables for stress:

loj-BAN — wrong LOJ-ban — correct (lojban has 2 syllables: loj-ban, stress on first = penultimate)

For cmavo:

• No mandatory stress; conventional stress is on the first vowel
• Two-syllable cmavo like ki'a, ta'e, ca'o stress the first vowel: KI'a, TA'e, CA'o

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Syllabic Consonants#

The consonants l, m, n, and r can be syllabic — that is, they can form a syllable nucleus when surrounded by consonants, replacing what would otherwise be an uncomfortable consonant cluster:

bridi — the r is not syllabic (it has vowels on both sides) ta'onai — not syllabic prali — the r can be syllabic in some clusters

In standard pronunciation, when one of these consonants appears between two consonants with no vowel, it is pronounced with a faint schwa-like quality.

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Consonant Clusters#

Lojban allows consonant clusters, but only permissible pairs. The rules:

General permissibility test for any CC pair: A pair is permissible unless it:

• Contains two identical consonants (pp, tt, etc.)
• Mixes a voiced and unvoiced member of the same stop/fricative pair: bd, pb, dt, td, gk, kg, vf, fv, zs, sz, jc, cj
• Contains cx or xc (sibilant+velar fricative combinations)
• Contains mz, nz, nm, mn (nasal+sibilant combinations: only ns and nz are allowed)

Permissible initial clusters (full list):

Initial clusters are the stricter subset used at the start of a word or syllable (in gismu, lujvo, and fu'ivla). There are exactly 48 permissible initial pairs:

The complete 48 (in alphabetical order): bl, br, cf, ck, cl, cm, cn, cp, cr, ct, dj, dl, dm, dn, dr, dv, dz, fl, fr, gl, gn, gr, jb, jd, jg, jm, jv, kl, kr, ml, mr, pl, pr, sf, sk, sl, sm, sn, sp, sr, st, sv, tc, tr, ts, vl, vr, xl, xr, zb, zd, zg, zm, zn, zv.

These are the only clusters that may begin a word or syllable. All other combinations require a vowel (usually y) inserted between them.

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Vowel Pairs: Diphthongs vs. Apostrophe Pairs#

Two adjacent vowels in Lojban are either a diphthong (one syllable) or a VV pair (two syllables, separated by apostrophe /h/):

Diphthongs — one syllable, no apostrophe:

These four only occur in Lojban cmavo and attitudinals. Any other vowel combination in a native Lojban word requires an apostrophe to separate the syllables.

VV pairs with apostrophe — two syllables:

All other adjacent vowel combinations in native Lojban words must use an apostrophe:

• u'i, a'i, o'e, i'e, e'a, etc.
• The apostrophe represents /h/ between the vowels: u'i = /u.hi/

In names (cmene): vowel pairs without apostrophe are permitted when the source language has them. A comma may be used in writing to indicate that two vowels are in separate syllables without implying /h/ pronunciation: .ei,u = three separate sounds, no diphthong and no /h/.

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Buffer Vowel Insertion#

When Lojban requires a vowel to break up an impermissible consonant cluster (in lujvo, cmene, or fu'ivla), the buffer vowel y is used in most cases:

pante + tavla → patyta'a (not patta'a — tt is illegal) mudri + siclu → mudysiclu

The choice of buffer:

• y (schwa): standard in lujvo; it is morphologically transparent and doesn't carry stress
• i or u: used in names when y would feel unnatural or when the source language vowel is closer

In names, the buffer vowel is chosen to match the source phonology as closely as possible. The key rule is simply: every consonant pair in the result must be permissible.

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Syllabication Algorithm#

To determine where syllable breaks fall — which determines stress — Lojban uses a greedy algorithm:

1. Start from the left.
2. At each point between two consonants in a VC₁C₂V sequence: if C₁C₂ is a permissible initial cluster, the break is before C₁ (both consonants go to the next syllable: V | C₁C₂V).
3. If C₁C₂ is not a permissible initial cluster, the break is between C₁ and C₂ (VC₁ | C₂V).

Example: ta-vla — vl is a permissible initial pair → break before v → /tav.la/ — oops, that gives vl at the start of the second syllable which is correct: tav-la → stress on first syllable tav.

Example: mlatu — ml is a permissible initial pair → no break before ml, so: mla-tu → stress on mla.

Example: bridi — br is a permissible initial → bri-di → stress on bri.

Example: lojban — jb is a permissible initial → loj-ban → only 2 syllables → stress on first = LOJ-ban.

This algorithm determines which syllable is penultimate, which always receives stress in brivla.

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Audio-Visual Isomorphism#

Lojban is designed to be "audio-visual isomorphic" — what you write is exactly what you say, and vice versa. There is no silent letters, no irregular spelling, no homophone confusion. Every spoken Lojban sentence can be transcribed into written Lojban and back without any ambiguity.

This is why:

• The apostrophe (for /h/) must be written every time it's pronounced
• The period (pause) must be written before vowel-initial words
• Stress is regular and predictable — never needs marking

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Allophones and Variation#

Lojban phonology specifies phoneme targets but allows considerable phonetic variation:

• r can be any r-sound: trilled /r/, flapped /ɾ/, retroflex /ɻ/, approximant /ɹ/
• n before k/g can be /ŋ/ (as in English sing)
• Vowels may be somewhat lax in unstressed syllables
• l can be clear or dark

The key is that each sound must be distinguishable from all others. Lojban does not require "perfect" pronunciation — only distinct pronunciation.

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Summary#

• English-first learners: see If English is your first language — c/j/x/g/y, diphthongs as one syllable, . = pause