A
syllable in Esperanto is generally of the form (s/ŝ)(C)(C)V(C)(C). That is, it
may have an
onset, of up to three consonants;
must have a
nucleus of a single vowel or diphthong (except in
onomatopoeic words such as
zzz!), and may have a
coda of zero to one (occasionally two) consonants. Any consonant may occur initially, with the exception of
j before
i (though there is now one word that violates this restriction, ('Yiddish') which contrasts with "of an offspring"). Any consonant except
h may close a syllable, though coda
ĝ and
ĵ are rare in monomorphemes (they contrast in 'age' vs. 'thing'). Within a morpheme, there may be a maximum of four sequential consonants, as for example in ('teaches'), ('to the right'). Clusters of three consonants include the
sibilant s in second position, or one of the
liquids (
l,
r) or
v (for
kv or
gv) in final position; clusters of four consonants require both.
Geminate consonants generally only occur in polymorphemic words, such as ('short'), ('to flop down'), ('to mis-write'); in
ethnonyms such as ('a Finn'), ('a Gaul') (now more commonly ); in
proper names such as ('Schiller'), ('Buddha', now more commonly ); and in a handful of unstable borrowings such as ('a sports match'). In compounds of
lexical words, Zamenhof separated identical consonants with an epenthetic vowel, as in ('the evening of life'), never . Word-final consonants occur, though final voiced
obstruents are generally rejected. For example, Latin ('to') became Esperanto , and Polish ('than') morphed into Esperanto ('than').
Sonorants and voiceless obstruents, on the other hand, are found in many of the numerals: ('hundred'), ('eight'), ('seven'), ('six'), ('five'), ('four'); also ('during'), ('even'). Even the poetic elision of final
-o is rarely seen if it would leave a final voiced obstruent. A very few words with final voiced obstruents do occur, such as ('but') and ('next to'), but in such cases there is no minimal-pair contrast with a voiceless counterpart (that is, there is no or to cause confusion). This is because many people, including most Slavs and Germans, do not contrast voicing in final obstruents. For similar reasons, sequences of
obstruents with mixed voicing are not found in Zamenhofian compounds, apart from numerals and grammatical forms, thus 'for a long time', not . (Note that is an exception to this rule, like in the Slavic languages. It is effectively ambiguous between fricative and approximant. The other exception is , which is commonly treated as .) Syllabic consonants occur only as
interjections and
onomatopoeia: . All triconsonantal onsets begin with a sibilant,
s or
ŝ. Disregarding proper names, such as , the following initial consonant clusters occur: • Stop + liquid –
bl, br; pl, pr; dr; tr; gl, gr; kl, kr • Voiceless fricative + liquid –
fl, fr; sl; ŝl, ŝr • Voiceless sibilant + voiceless stop (+ liquid) –
sc ,
sp, spl, spr; st, str; sk, skl, skr; ŝp, ŝpr; ŝt, ŝtr • Obstruent + nasal –
gn, kn, sm, sn, ŝm, ŝn • Obstruent + –
gv, kv, sv, ŝv And more marginally, :Consonant + –
(tj), ĉj, fj, vj, nj Although it does not occur initially, the sequence is pronounced as an affricate, as in ('a husband') with an open first syllable [e], not as . In addition, initial occurs in German-derived ('penny'), in
Sanskrit ('
kshatriya'), and several additional uncommon initial clusters occur in technical words of
Greek origin, such as
mn-, pn-, ks-, ps-, sf-, ft-, kt-, pt-, bd-, such as ('a sphincter' which also has the coda ). Quite a few more clusters turn up in sufficiently obscure words, such as in "Thlaspi" (a
genus of herb), and
Aztec deities such as ('Tlaloc'). (The phonemes are presumably devoiced in these words.) As this might suggest, greater phonotactic diversity and complexity is tolerated in learnèd than in quotidian words, almost as if "difficult" phonotactics were an iconic indication of "difficult" vocabulary. Diconsonantal codas, for example, generally only occur in technical terms, proper names, and in geographical and ethnic terms: ('a conjunction'), ('Arctic'), ('isthmus'). However, there is a strong tendency for more basic terms to avoid coda clusters, although ('hundred'), ('after'), ('holy'), and the prefix ('ex-') (which can be used as an interjection: 'Down with the king!') are exceptions. Even when coda clusters occur in the source languages, they are often eliminated in Esperanto. For instance, many European languages have words relating to "body" with a root of . This root gave rise to two words in Esperanto, neither of which keep the full cluster: ('a military corps') (retaining the original Latin
u), and ('a biological body') (losing the
s). Many ordinary roots end in two or three consonants, such as ('a bicycle'), ('a shoulder'), ('a needle'), ('to cut'). However, these roots do not normally entail coda clusters except when followed by another consonant in compounds, or with poetic elision of the final
-o. Even then, only sequences with decreasing
sonority are possible, so although poetic occurs, *, *, and * do not. (Note that the humorous jargon does not follow this restriction, because it elides the grammatical suffix of all nouns no matter how awkward the result.) Within compounds, an
epenthetic vowel is added to break up what would otherwise be unacceptable clusters of consonants. This vowel is most commonly the nominal affix
-o, regardless of number or case, as in ('a songbird') (the root , 'to sing', is inherently a verb), but other part-of-speech endings may be used when
-o- is judged to be grammatically inappropriate, as in ('expensive'). There is a great deal of personal variation as to when an epenthetic vowel is used. ==Allophonic variation==