Latin uses no articles, but Vulgar Latin does. It is not clear when exactly this change occurred, but the articles are clearly derived from Latin's demonstrative adjectives, ille and illa (and in the case of Sardinian, ipse and ipsa, which became su and sa). In all cases except Romanian, the article precedes the noun. (In Romanian it is attached to the rear of the noun, probably because of influence from neighboring Balkan tongues.) Some scholars believe that the influence of Greek (which has articles) affected how Medieval Latin evolved to facilitate the translation of New Testament scriptures. Evidence that the demonstratives were in use colloquially as articles comes from the trend in written Medieval Latin to use much stronger demonstratives than "ille" when a demonstrative was called for. They used terms like "supradictus" ("above-mentioned") instead, probably because the simple demonstratives had lost their older meanings of "this" or "that." In every case of Vulgar Latin, the number "one" came to mean the indefinite article. This trend was perceptible even in the Classical period, when "quiddam" meaning "a certain one" was being supplanted by "unus."
The loss or softening of many unstressed vowels also led to a glossing over of distinctions among genders and declensions. The "um" ending for neuters became "o" in Vulgar Latin, as did the "us" ending. Neuter plurals (ending in -a, like "stamina") were often reanalyzed as feminine singulars. Third declension neuter nouns were absorbed into other genders, but inconsistently (accounting for the fact that a word like "lacte" (or "lactem") meaning "milk" has become masculine in French, Portuguese and Italian, and feminine in Spanish). Usually, as in the case of "milk," the transfer was made with the stem of the noun, which was the basis for the accusative form. Sometimes, however, the nominative form was to source of the change, as in the word "nomen / nomine." The word for "name" has been derived in all Romance languages from the nominative (as in "nom" in French and "nome" in Italian and Portuguese), except for Spanish (where "nombre" is derived from "nomine").
Many changes in the form and gender of nouns occurred out of a need to simplify formal Latin and eradicate many irregularities. For example, tree names in Latin were feminine nouns in the second declension (with masculine endings). They simply became masculine nouns (like "el peral" and "el manzano" in Spanish) or kept their femininity, but acquired feminine form as well ("a pereira," "a maciera" in Portuguese). Another stumbling block, the fourth declension noun "manus /manuus" (hand), is feminine, and survived in Vulgar Latin as a feminine noun with masculine form, probably because of its frequent use in daily speech. Even though the neuter noun was wiped out in Vulgar Latin, it is evident that neuter pronouns still existed, as they still can be found in modern romance languages (like "esto" in Spanish).
The phonetic changes in Vulgar Latin made it virtually impossible to keep the distinctions of the various noun case endings, so the declension system basically disappeared. For a while, Vulgar Latin retained a different inflection for nouns in the genitive and dative, but even that eventually faded out. A hint of it can still be seen in the "le" pronoun in Spanish, which is an indirect object pronoun. To make up for the loss of inflection, word order became essential to meaning. In Classical Latin, the case endings told the hearer what was the subject, the direct object, and the objects of prepositions. Now it became increasingly important to use a sentence structure that would provide this information.
Plural formation in Classical Latin was part of the declension system, lost in Vulgar Latin when the cases themselves stopped being observed. Outside of Italy, the "s" was used, as it was a remnant of accusative plurals (like "-as" or "-os" for all declensions). From Italy east (including Sardinia and Romania, among others), plurals were formed by changing the final letter of the noun, as in "ragazza" becoming "raggazze" in the plural.
Prepositions sprouted up all over the place as the case system went away. A genitive (possessive) idea could be expressed in some cases by the possessive pronouns ("mea culpa") or by a prepositional phrase (like "the guilt of me"). New prepositions were forged from old ones, as in the case of "desde" (de-ex-de) and "depois" or "despuÃ©s" or "dopo" or "depuis" (de-ex-post). A Band-Aid for the loss of dative was sometimes applied, the use of "ad" plus an accusative.
Adverbs were often made out of adjectives in Classical Latin by adding "er" or some other form, as in the case of "acriter" from "acer" and "fortiter" from "fortis." In Vulgar Latin, these many variable approaches gave way to just one: The use of "mente" (the ablative of the word for "mind"). This word meant literally "with a ________ mind." So "acer" no longer became "acriter" but rather "acer mente" - with a fierce mind. Even during the Classical period of Latin this form was in occasional use, and Vulgar Latin just regularized it. Eventually the two words in the phrase were joined into a single word, usually using the feminine singular root of the adjective.
Verbs did not suffer as much change as the other parts of speech in Vulgar Latin. Part of the reason is that Vulgar Latin's strongly stressed syllable would change around with various persons, numbers and tenses, so that unstressed vowels tended to have stressed roles in some instances; hence they would not atrophy. Final consonants tended to disappear, following a trend started much earlier in Latin (and found even in ancient graffiti). Thus, "amarunt" became "amarun" and later "amaron." The merger of the "b" sound and the "v" sound made the imperfect and the future tense sound alike, so the trend in Vulgar Latin was to form the future with the help of "habeo, habere." For example, "amare habeo" came to be the way to say "I will love" (literally, "to love I have"). The "habeo" became "he" or "ai" or "hei" (as it still remains in Spanish, French and Portuguese) or "ho" in Italian. The contraction of the forms to amarÃ©, aimerai, amarei and amerÃ² was just a question of time. Even now, Portuguese permits the "opening up" of the tense with the pronoun, as in "amar-te-ei" for "I will love you." The conditional tense also developed along the same lines, with the same rules, and the same results. The form of "habere" used was the imperfect as in amare habebam, which became amarais in French, amarÃa in Spanish and amaria in Portuguese. Vulgar Latin in Italy came to use the perfect form, "habuit," which led to the ending "ebbe" as in "io amarebbe," for "I would love." Portuguese shows the historical evolution here as well, with the permitted insertion of the pronoun before the ending, as in "comÃª-lo-ia" for "I would eat it."
The passive form of verbs ("-tur" in Latin) fell by the wayside in the evolution to Vulgar Latin. Instead a Germanic approach - helping verb plus a passive participle - became the norm. The helping verb was "essere," to be. An alternative form, using the reflexive, also grew up during the time that Vulgar Latin was the lingua franca of Europe.
Vulgar Latin also felt free to mix up the verbs a bit. The three Latin words for "go" - ire, vadere and ambulare - were stirred together, not always consistently. Today a vestige can be seen in Iberian tongues that mix vadere and ire (as in "vaya" -- an imperative form of "ir"), and in Italian tongues in which ambulare and ire come out as "andare." In French, pieces of each verb can be found amongst the various forms of the conjugation of aller.
Copula means "linking verb." English has "to be," so one can "be sad" (temporarily) or "be sad" (as a matter of one's nature). Vulgar Latin imported two verbs from Latin to express these two circumstances. "essere" (the Latin verb "to be") was used for inherent or permanent traits of something, that is, "its essence." "Stare" (the Latin verb "to stand") was used for temporary traits and descriptions of the location of an object - the momentary "statics" of a noun. So describing a person's sadness with "stare" meant he or she was in a sad mood. Describing the person with "essere" meant that he or she was a sad person by nature. This distinction caused great consternation among English speakers trying to learn a Romance language (other than French). The potential for confusion has not been helped by modern developments, either. For example, in Spanish, "estar" is always used for the location of anything, even a castle. In Portuguese, "estar" is used for movable things that happen to be in a specific location, but "ser" is used for permanently situated things, like castles, cathedrals and other buildings. Classical Latin did not draw these distinctions in this way, but in Vulgar Latin they developed as a quite normal means of expressing linking verbs. Interestingly, in French, "essere" and "stare" merged at some later juncture to become "Ãªtre."