Common Latin Noun Declensions

Why This Matters

Latin noun declensions aren't just arbitrary endings to memorize—they're the grammatical DNA that tells you how every noun functions in a sentence. When you see a noun in Latin, its ending reveals its case (subject? object? possession?), its number (singular or plural?), and often its gender. Without recognizing these patterns, you'll struggle to parse even simple sentences, and translation becomes guesswork.

Here's the key insight: each declension is defined by its stem vowel, and that stem determines the entire pattern of endings. You're being tested on your ability to identify which declension a noun belongs to (hint: check the genitive singular), recall the correct endings for each case, and apply agreement rules with adjectives and verbs. Don't just memorize charts—know what makes each declension distinctive and where they overlap or diverge.

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The -A Stem: First Declension

The first declension is your entry point into Latin nouns. Almost all first declension nouns are feminine, with the characteristic -a ending in the nominative singular serving as your primary identifier.

Puella, Puellae (Girl)

• Nominative singular -a, genitive singular -ae—this genitive ending is how you confirm a noun belongs to the first declension
• Predominantly feminine gender—even when referring to occupations like agricola (farmer) or nauta (sailor), these nouns remain grammatically feminine in form but can denote males
• Plural nominative/genitive identical (-ae)—context determines whether you're reading "the girls" (nominative) or "of the girl" (genitive singular)

Terra, Terrae (Land)

• Abstract and concrete nouns alike—first declension handles everything from patria (fatherland) to aqua (water)
• Dative and ablative plural share -īs ending—the long vowel distinguishes these forms and appears across all five declensions in these cases
• Foundation for adjective agreement—first declension endings pair with first/second declension adjectives (magna terra, great land)

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The -O Stem: Second Declension

The second declension splits into two patterns based on gender: masculine nouns ending in -us and neuter nouns ending in -um. The genitive singular -ī confirms membership in this declension for both types.

Servus, Servī (Slave/Servant)

• Nominative -us, genitive -ī pattern—the most common masculine noun type you'll encounter in elementary Latin
• Vocative singular exception: -e—when directly addressing someone, serve! not servus! (one of the few cases where vocative differs from nominative)
• Plural nominative -ī vs. genitive -ōrum—don't confuse the short plural nominative with the genitive singular

Bellum, Bellī (War)

• Neuter nominative and accusative always identical—this rule applies across ALL declensions and is heavily tested
• Neuter plural nominative/accusative ends in -a—bella means both "wars" (subject) and "wars" (direct object)
• Same genitive as masculine (-ī)—confirms second declension membership regardless of gender

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The Consonant and I-Stems: Third Declension

Third declension is the most diverse and challenging group. The nominative singular varies wildly, but the genitive singular -is is your anchor. This declension includes masculine, feminine, AND neuter nouns with no predictable nominative pattern.

Rēx, Rēgis (King)

• Genitive -is is the identifying marker—when the nominative gives you no clue (rēx, nōmen, corpus), the genitive reveals all
• Masculine/feminine plural nominative -ēs—distinguishes these from neuter plurals ending in -a
• Stem often differs from nominative—rēx becomes rēg- in all other forms; you must memorize the genitive to find the true stem

Nōmen, Nōminis (Name)

• Neuter third declension follows the universal neuter rule—nominative and accusative identical (nōmen/nōmen singular, nōmina/nōmina plural)
• Stem revealed in genitive: nōmin-—this stem appears in all forms except nominative/accusative singular
• I-stem variants exist—some third declension nouns (like mare, maris) have slightly different endings; watch for genitive plural -ium instead of -um

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The -U Stem: Fourth Declension

Fourth declension is smaller but important, featuring masculine nouns in -us and rare neuters in -ū. The genitive singular -ūs (with a long vowel) distinguishes it from second declension's -ī.

Manus, Manūs (Hand)

• Genitive singular -ūs distinguishes from second declension—manus looks like second declension servus, but the genitive reveals the truth
• Feminine despite -us ending—one of the few fourth declension nouns that breaks the masculine pattern; domus (house) is another
• Nominative and genitive singular look identical—only vowel length differs (manus short vs. manūs long); context is crucial

Cornū, Cornūs (Horn)

• Neuter fourth declension is rare—you'll mainly see cornū and genū (knee)
• Nominative singular -ū, plural -ua—follows the neuter pattern of matching nominative/accusative
• Military and technical vocabulary—fourth declension appears frequently in descriptions of armies (exercitus), government (senātus), and body parts

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The -Ē Stem: Fifth Declension

The smallest declension, fifth declension contains mostly feminine nouns with the distinctive genitive singular -ēī (or -eī). You'll encounter these less frequently, but they include high-frequency vocabulary.

Diēs, Diēī (Day)

• Can be masculine or feminine—diēs is masculine when referring to a specific/appointed day, feminine when meaning "time" generally
• Genitive -ēī is the identifier—no other declension uses this ending
• Limited membership—only diēs and rēs (thing, matter) are commonly used; most fifth declension nouns are rare

Rēs, Reī (Thing, Matter, Affair)

• Appears in essential phrases—rēs pūblica (republic, literally "public thing"), rēs gestae (deeds accomplished)
• Highly versatile meaning—can translate as thing, matter, affair, situation, or circumstance depending on context
• Same endings as diēs throughout—if you know one fifth declension noun, you know them all

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Quick Reference Table

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Self-Check Questions

1. You encounter the noun exercitus with genitive exercitūs. What declension is it, and how do you know it's not second declension despite the -us nominative ending?

2. Which two declensions contain primarily feminine nouns, and what are their characteristic genitive singular endings?

3. Compare and contrast how neuter nouns behave in second declension (bellum) versus third declension (nōmen)—what rule do they share, and how do their plural forms differ?

4. A student sees agricolam and assumes it's feminine because it's first declension. Explain why this creates a translation problem and how natural vs. grammatical gender works.

5. If an FRQ asks you to identify the case of manūs in a sentence, what challenge does this form present, and what strategies would you use to determine whether it's nominative singular, genitive singular, or nominative plural?