The Evolution of the Latin Conjugations

Introduction

When we first learn Latin, the system of verbs is laid out for us in such an orderly fashion. Four conjugations. Four principal parts. It just makes sense, right? It feels intentional. Systematically structured, just like Roman society. But this appearance is just an illusion. The Latin verb system we memorize today is just the end result of years and years of linguistic evolution. Like any other language, Latin's verb system didn't just appear fully formed.

Before Conjugations Existed

In order to understand Latin's conjugations, we must begin at a stage when verbs followed completely different rules.

I'll have to keep this description a little simple here, as PIE's grammatical system is truly vast. In PIE, verbs used several stems, each expressing a different aspect of action. Ablaut, a form of vowel gradation (changing the vowel from e to o to no vowel), gave the verb a different grammatical function. This matters for Latin because Latin keeps the idea of multiple verbal stems. The Latin present system (infectum) descends from PIE present forms, while the perfect system (perfectum) descends from PIE perfect and aorist forms. PIE verbs would either add endings directly to the root (athematic) or use a connecting vowel (thematic). Latin's irregular verbs, like sum (I am) and volo (I want), still retain certain features of these archaic patterns, such as irregular verb endings. So, Latin inherited a verb system that was built on multiple stem types, and the differences among these stems were often a result of ablaut. Latin later reorganized this into the infectum and perfectum systems, but the underlying dual-stem architecture is part of PIE's legacy.

The Creation of Verbal Classes

Of course, PIE didn't directly evolve into Latin. As you might expect, there was a sort of "middleman," that being Proto-Italic. Proto-Italic was spoken across the Italian peninsula before the rise of Rome. This phase represents the middle ground where the older Indo-European system began to simplify into something closer to what we know as Latin.

To put it simply, Proto-Italic took the complex PIE patterns and made them more predictable. Instead of having many different stems that had similar jobs, Proto-Italic began to use a few main stem forms. The vowel that connected the stem to its ending -- or the "theme vowel" -- became much more stable, and the dramatic ablaut system of PIE began to play less and less of a role. The language started to settle into habits. This increasing predictability made it easier for speakers to quickly recognize verb forms, making everyday communication easier.

Latin's sister languages also display this. Oscan and Umbrian have verb endings and stem patterns that closely resemble early Latin. These languages helped confirm the notion that Latin's conjugation classes were taking shape long before Rome itself.

Modern tools, like comparative linguistics and datasets like PILA, help scholars connect these early Proto-Italic forms to their Latin descendants. They help give us a clearer picture of how Latin reshaped and standardized the patterns that would eventually come to be known as the four conjugations.

Solidification of the Four Conjugations By around the 3rd century BCE, Latin's verb system settled into that classic four-conjugation system that modern students are familiar with. These conjugations were defined by distinct endings for their infinitive (2nd p.p.) form. It went as follows: āre for the 1st conjugation, ‑ēre for the 2nd conjugation, ‑ere for the 3rd conjugation (while this may appear the same as the 2nd conjugation at a glance, pay attention to the macron, which denotes a long e for the 2nd conjugation), and ‑īre for the 4th conjugation. As you can see, each conjugation had a specific theme vowel that influenced the formation of other tenses. This theme vowel would link the verb stem to its endings.

As I previously referenced, Latin's verb system operated in two major domains: the infectum and the perfectum. The infectum system was comprised of the present, imperfect, and future forms, which all draw from the verb's present stem. It dealt with ongoing or incomplete actions. The perfectum system consisted of the perfect, pluperfect, and future perfect forms, and is derived from the verb's perfect stem (the 3rd principal part). In Latin, the principal parts compress these layers into a teachable set of 4 forms with various endings applied for person and number.

Even after this system was stabilized, Latin still had traces of earlier linguistic phases. Some verbs sat between conjugations, like the mixed 3rd -io conjugation (e.g., capio [1st p.p.], capere [2nd p.p.]), which behaves partly like the 3rd conjugation and partly like the 4th. Suppletive verbs, like sum, draw their principal parts from historically unrelated words. This is why their forms can seem unpredictable. These irregular verb types show how the language preserves some elements of the past.

Grammatical Standardization

As the Latin language thrived, Roman grammarians took on the grand task of describing and teaching it. In the 1st century BCE, Marcus Terentius Varro categorized verbs based on observable patterns of vowels and stems. In the 4th century CE, Aelius Donatus created the Ars Minor, a grammar textbook that became the foundation for Latin education. In the 6th century CE, Priscian would expand these classifications into a comprehensive 18-volume treatise on Latin grammar called the Institutiones [nominative, plural] grammaticae [genitive, singular](Institutes of Grammar). This was the largest work of Latin grammar from antiquity and was highly influential in the Middle Ages for teaching Latin and grammatical study. Their efforts would ensure that the complex system of Latin verbs was conveyed consistently to any future Latin scholar.

So, while Latin's standardized conjugations may seem orderly at first, they have a long history that begins with PIE's stems and ablaut system and ends with the grammatical standardization by Roman grammarians. While many students of Latin won't think twice about how or why the various conjugations even came to exist, understanding the centuries of linguistic evolution that resulted in their formation turns a set of memorizable patterns into a story of linguistic growth.