A late 3rd century work, called the "Appendix Probi," goes to the trouble of advising against mispronunciations of formal Latin. It is assumed that these "mispronunciations" were common corruptions that came to form Vulgar Latin. Some of the problems identified in the Appendix Probi are:
- Merger of long /e/ and short /i/ (for example, saying "vinea" as if it were spelled "vinia."), and the reverse situation of lowering /i/ to /e/ as in "demedius" instead of "dimidius." A similar trend occurs between /o/ and /u/, such as pronouncing "coluber" as if it were "colober." Another confusion was between /b/ and /v/ -- which today are identical in Spanish. There was an evident tendency in the 2nd century to say "brabium" for "bravium."
- Loss of nasal consonants at the end of interior syllables, as in "mensa" being converted to "mesa."
- Loss of initial and internal /h/ as in "ostia" rather than "hostia" and "aduc" rather than "ad huc."
- Syncope - the suppression of internal unstressed vowels (as converting "masculus" to "masclus."
- Apocope - the suppression of final sounds (in this case, mainly final "t" and "s" as well as the final "m" that seems to have been barely pronounced even in Classical times).
- Use of diminutives for nouns that did not carry an "a" or "o" ending, so that people would know the gender. For example, "auris" became "oricla" ("oreja" in modern Spanish).
Palatalization is the converting of hard consonants, usually dentals and alveolar sounds, into softer forms, usually affricates, by placing the tongue closer to the palate than the front of the mouth. In this way, "ti" became "tzi" and "c" became "chi" as in modern Italian. Portuguese in Brazil also palatizes "ti" and "te" to "chi" and "di" and de" to "dgi." In IPA terms, the changes are: [ts] to [tʃ] and [dz] to [dʒ]. Thus "caelum" [kailu(m)] (sky or heaven) became "cielo" [tʃɛlo] in Italian and "cielo" [sjelo] in Spanish. This process began during the period of Vulgar Latin, and the exact form of palatalization depended in part upon the region of the speech. The "ti" and "chi" of "Church Latin" came into use in the second through the fourth centuries.
Lenition is the weakening or softening of consonants, particularly when they separate two vowels. For example, the unvoiced plosives (p, t, c) became voiced (b, d, g) and in some cases further lenited to the approximants [β], [Ã°] and [ɣ], respectively. The intervocalic, unvoiced "s" would be voiced as well, to a "z" sound, as in "casa" [kɑzɑ] in Italian. Double plosives and the sibilant became single ("pp" for example, became just p and "ss" became "s"). "B" and "V" between vowels became a fricative [β], though later Spanish merged them back to a single, plosive phoneme.
Fortition is the strengthening of a sound. It is the opposite of lenition. The "j" - which in Latin had been but a semi-vowel allophone of "i" - became its own, stronger sound, a fricative, and a separate phoneme altogether.
Prosthesis is the tendency to add an extra sound before or after another. When a Spanish speaker pronounces English words, there is a tendency to add a prosthetic "e" before words beginning with "st" or "sp." This is because in Spanish, a prosthetic "e" has been added to the "sp" and "st" sounds to create different phonemes. Thus, in Spanish, the "e" is placed before many Latin words (for example, "spatha" (sword) became "espada.")
Stressed Vowels underwent considerable change from Latin. The distinction between long vowels and short vowels, so important in Classical Latin, disappeared. The near-close vowels (ĭ and ŭ) opened up and became more like ē and ō. Linguists provide the example of "pira" (pear) and "vera" (true). In Vulgar Latin they became pera and vera, and rhymed. The same would be true of "nux" (nut) and "vox" (voice), which rhymed in Vulgar Latin, and in modern times became noix and voix in French, noz and voz in Portuguese, and so on. Another influence was stress. Vulgar Latin put more stress on the vowel in accented position, causing unstressed vowels to have less importance for meaning, and causing them to become ambiguous, muddy, or inaudible. The strongly stressed vowels in some cases led to the creation of diphthongs, as in the Italian word for "fire" - "fuoco" - which derives from Latin "foco." The strong "ae" sound in Latin became an "ie" diphthong in Italian (as in "lieta" for "happy" from "laeta"). In all, the ten classical Latin vowels (not counting "y") were reduced to approximately seven in Vulgar Latin, and from there to different numbers according to the language into which they evolved (for example, 5 in Spanish and 6 in Romanian).
Unstressed vowels had their own changes in Vulgar Latin. The tendency was to retain the five short Latin vowels in unstressed positions for the Latin that became Spanish and Italian. French, Occitan and Portuguese showed different trends. (unstressed o and a becoming [u] and [ɔ] in Occitan; unstressed o and e becoming [u] and [i] (or [ɨ]) in Portuguese), and many unstressed finals becoming a schwa [ə] in French).