Latin Grammar Mini-Series | Lesson 7 - Understanding and "fleshing-out" the Third Declension in Latin

Third declension is Latin’s “catch-all” category for nouns. Into it have been put all nouns whose bases end with consonants -- yep, any consonant! That makes third declension very different from first and second declension. First declension, as you’ll remember, is dominated by a-stem nouns like femina and cura. Second declension is dominated by o- or u-stem nouns like amicus or oculus. Because of those vowels, we are given a bit of consistency within those declensions… The same is not true of third declension where one form, the nominative singular, is affected by the fact that its ending -s runs into the wide variety of consonants found at the ends of the bases of third-declension nouns, and the collision of those consonants causes irregular forms to appear in the nominative singular. 

That’s the (malus) bad news. 

The (bonus) good news is that only one case and number is affected by this, the nominative singular. 

All the other case endings begin with vowels, and consonants-running-into-vowels does not create the same kind of problem that consonants-running-into-consonants does. 

Thus, after the nominative singular, third-declension forms are regular and predictable.(Yay!)

Let’s look at some patterns that are useful in helping you memorize irregular third declension nominative singular forms.

If a base ends in -g- or -c-, when it’s combined with a nominative singular ending -s, normally the nominative singular ending will appear as -x, such as rex, regis, meaning “king” or lex, legis, meaning “law,” pax, pacis, meaning “peace,” vox, vocis, meaning “voice,” dux, ducis, meaning “leader,” and lux, lucis, meaning “light.” 

If the base ends in -t-, -nt-, or -d- and runs into the -s, most often what will happen is the nominative singular will end in -s, sometimes -ns, such as virtus, virtutis, meaning “courage,” civitas, civitatis, meaning “state,” salus, salutis, meaning “health,” and laus, laudis, meaning “praise.” 

If the base ends in -on- or -in- and runs into the -s, it will contract down all the way to the letter -o such as: homo, hominis, meaning “human,” virgo, virginis, meaning “girl,” or the name Cicero, Ciceronis, meaning “Cicero,” the great Roman orator. 

If the base ends in -r-, when -s is added, the nominative singular will be -er, as in pater, patris, meaning “father,” mater, matris, meaning “mother,” and frater, fratris, meaning “brother.” 4 

If the base ends in -ar- with -s added, it will remain as -ar, as in Caesar, Caesaris, meaning “Caesar” the Roman general, or exemplar, exemplaris, meaning “example.” 

If the base ends -or and is a masculine or feminine noun, with -s added it stays as -or, as in labor, laboris, meaning “work,” amor, amoris, meaning “love,” and soror, sororis, meaning "sister.” • If the word is -or or -er and is neuter, with -s added it will change to -us ─ remember there’s no ending being added here so it’s actually a different contraction from amor or labor ─ such as tempus, temporis, meaning “time,” corpus, corporis, meaning “body,” opus, operis, meaning “work,” and genus, generis, meaning “sort” or “kind.” 

If the base ends in -it- and -s- is added, the result will be either -es or -ut, as in miles, militis, meaning “soldier,” or caput, capitis, meaning “head.” 

If the base ends -ul or -ol and -s is added, the result is either -ul or -ol in the nominative singular, such as sol, solis, meaning “sun,” or consul, consulis, meaning “consul,” a high executive officer in Roman government. This should drive home the point that third declension is a “catch-all” category and, if all these irregularities make third declension seem overly complicated, remember that these irregularities involve only the nominative singular. If these patterns do not help you in memorizing, please feel free to ignore them.