Latin, like all languages, has changed over time. Today we say there have been seven periods of Latin history, but eight ages. The dates aren't set in stone, but they are an approximation of when each age switched to the next.
OLD LATIN (Birth of Latin-80 BC)
Also known as Archaic Latin, Old Latin is Latin's earliest stage. Rules of grammar were still being formed and kinks were still being sorted out. Below we see the paradigm of cases for the Old Latin word familia.
We still see the effects of Old Latin lingering in future periods of Latin. For instance, the Old Latin phrase pater familias, which means father of the family, contracted to paterfamilias, a word that existed throughout Latin history. Paterfamilias was even assimilated into English vocabulary, meaning the head of the household.
We also see that Old Latin used a lot of o's, which would later turn into u's. For instance, we have this conjugations paradigm of the Old Latin som, which would become sum in Classical Latin.
Eventually, Old Latin resolved itself into a form much more recognizable today: Classical Latin.
CLASSICAL LATIN (80 BC-117 AD)
Classical Latin is marked by the vocabulary and grammar most familiar to us today. Below we see just how much the paradigms above had evolved.
When we first look at the Classical Latin paradigm for familia, it doesn't really seem like Latin evolved. Rather, it looks like Latin took a stem backwards, mutating their forms of words to have little to no distinction. While it's true that these forms are less distinct than their archaic ancestors, it can't really be argued that this was a step backwards for the Romans. They changed their forms of words to be more euphonic (pleasing to the ear). In doing so, they consolidated forms that had a similar purpose. The dative and ablative cases, for instance, have always been considered similar, so there wasn't much need for a distinction between the two.
Wilhelm Sigismund Teuffel conjectured in 1870 that Classical Latin had two ages, divided not by grammar or linguistic changes, but by literature. These ages are the Golden Age and the Silver Age.
- GOLDEN AGE (80 BC-14 AD) - The Golden Age was thought to have two parts itself: the Republican Period (also called the Ciceronian Period) and the Augustan Period. The Republican Period ended after Julius Caesar's assassination, and the Augustan Period ended after Augustus' death. Republican authors include Cicero, Julius Caesar, Lucretius, Cato the Younger, and Catullus. Augustan authors include Virgil, Horace, Livy, and Ovid. Each of the Republican and Augustan authors are taught extensively in modern Latin classes.
- SILVER AGE (14 AD-117 AD) - The Silver Age lasted from the death of Augustus to the death of Trajan. Notable Silver Age authors include Seneca, Pliny the Elder, Quintilian, Martial, Juvenal, and Tacitus. While these authors aren't taught so extensively today as the Golden Age authors, they are well-known.
VULGAR LATIN (117 AD-900 AD)
Classical Latin was the era of lofty Latin and great literature. However, when the Roman Empire started to decline in the third century AD, Latin should have gone down with it. The biggest reason Latin stuck around was because of how immense the Roman Empire had been. Different regions began to modify and specialize their dialects of Latin until they had a bunch of different languages. These were the Romance languages, including French, Italian, Portuguese, and Spanish. Unfortunately, as most Vulgar Latin speakers were illiterate, there is very little in the way of Vulgar Latin writings.
MEDIEVAL LATIN (900 AD-1300 AD)
Medieval Latin is the Latin of the Middle Ages, the Latin that was taken over and used by the Catholic Church. The Catholic Church made their own dialect of Latin now known as Church Latin or Ecclesiastical Latin, in which they decided that Latin liturgies sounded better with an Italian pronunciation. C's, which used to make a k sound now made a ch sound. V's, which sounded like w's now sounded like the modern v sound. Medieval Latin speakers also added the letter j and often consolidated the diphthong ae into e.
RENAISSANCE LATIN (1300 AD-1500 AD)
When the Renaissance rolled around, Latin had already changed drastically from its classical period. Diphthongs had been eliminated from Latin, and t's and c's sounded indistinguishable. The Renaissance sparked an interest in classical Greek and Roman cultures, and Renaissance-era writers started calling for a return to the ways of Classical Latin. Latin once again became the language of science and culture. The Renaissance set the stage for Latin to be the international language of science it is today and for Classical Latin (rather than Medieval Latin) to be taught in schools still to this day. Renaissance Latin is the primary reason why Latin is associated with scholarship and sophistication.
NEW LATIN (1500 AD-1900 AD)
Then we hit the New Latin (also called Neo-Latin) period. In the New Latin period, French and English arose as the most popularly spoken languages (hence why the most influential language of a time is called the lingua franca, Latin for the French language). Latin remained the standard for negotiations, business, and law. As French grew in power, Latin became more and more obsolete.
MODERN LATIN (1900 AD-present)
To this day, Latin is considered a "dead language"--no one's native tongue. Traces of Latin still remain in our more complicated vocabulary, and phrases are often directly incorporated into law jargon (such as ad hominem and habeas corpus), and used as mottoes for families, nations, and universities (E pluribus unum, crescat scientia vita excolatur). Latin is used extensively in the field of taxonomy. Latin enthusiasts also work to keep Latin up-to-date by using classical methods of Latin word formation to create Latin neologisms for modern conveniences (such as interrete for the Internet, telephonum for telephone, and tostrum for toaster).