rēx, rēgis: the third declension
Consonant stems, the genitive that holds the key, and the endings -is, -ī, -em, -e.
LatinIntermediate Latin · The third declensionAbout 4 min: 1 reading, 3 practiceUpdated
- Find the base of a third-declension noun from its genitive
- Decline masculine, feminine and neuter consonant stems
- Recognise the common nominative changes (rēg- → rēx, mīlit- → mīles, legiōn- → legiō, flūmin- → flūmen)
Latin Level 2: verbs and the other declensions: lesson 20 of 35
- Intermediate Latin · Verbs: the present system
- sum: I am, I was, I shall be 3 min
- The present of amō and moneō 4 min
- The imperfect: was doing 4 min
- The future: will do 3 min
- The dative with adjectives 3 min
- The present of regō and audiō 4 min
- The imperfect of regō and audiō, and verbs that take the dative 3 min
- The future of regō and audiō 3 min
- capiō, and giving orders 3 min
- Intermediate Latin · The passive voice
- The passive: being done to 3 min
- The passive of regō, audiō and capiō; passive infinitives 3 min
- Synopses, and the ablative of "from" 3 min
- Intermediate Latin · The perfect tenses
- fuī, fueram, fuerō: the perfect tenses of sum 3 min
- The perfect active: did, have done 5 min
- Had done, will have done: pluperfect and future perfect active 3 min
- amātus sum: the perfect passive 4 min
- Principal parts, prepositions, and yes-or-no questions 5 min
- possum, "I can", and the infinitive 3 min
- Intermediate Latin · Pronouns
- quī, quae, quod: who, which, that 4 min
- Intermediate Latin · The third declension
- rēx, rēgis: the third declension 4 min
- hostis, urbs, mare: i-stems 4 min
- vīs and iter; gender in the third declension 4 min
- omnis, ācer, pār: third-declension adjectives 3 min
- Intermediate Latin · The fourth and fifth declensions
- manus, cornū: the fourth declension 3 min
- Rōmae, domī, Athēnīs: place and the locative 4 min
- diēs, rēs: the fifth declension and the ablative of time 3 min
- Intermediate Latin · Pronouns
- ego, tū, sē: personal and reflexive pronouns 4 min
- ipse, "himself", and īdem, "the same" 3 min
- hic, iste, ille: this and that 4 min
- aliquis, quīdam, quisque: someone, a certain, each 3 min
- Intermediate Latin · Comparison
- clārior, clārissimus: comparing adjectives 4 min
- melior, optimus: irregular comparison, plūs, and "by how much" 3 min
- clārē, fortiter: adverbs and their comparison 4 min
- Intermediate Latin · Numerals
- ūnus, duo, trēs: numerals, "of" the whole, and "for how long" 5 min
- Intermediate Latin · Deponent verbs
- hortor, sequor: deponent verbs 3 min
Try first
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Pairs with D'Ooge, Latin for Beginners (Ginn, 1909), Lessons XXXIX–XLII, §§ 230–240
What it is
The third declension is the biggest in Latin. Its nominative singular comes in many shapes, so always learn the genitive with it: drop -is from the genitive and you have the base.
| Nominative | Genitive | Base |
|---|---|---|
| rēx, king | rēgis | rēg- |
| mīles, soldier | mīlitis | mīlit- |
| legiō, legion | legiōnis | legiōn- |
| pater, father | patris | patr- |
| flūmen, river | flūminis | flūmin- |
| tempus, time | temporis | tempor- |
Masculine and feminine nouns take these endings:
| Case | Singular | Plural |
|---|---|---|
| Nom. | rēx | rēgēs |
| Gen. | rēgis | rēgum |
| Dat. | rēgī | rēgibus |
| Acc. | rēgem | rēgēs |
| Abl. | rēge | rēgibus |
Neuters follow the rule you already know: the accusative is the same as the nominative, and the nominative and accusative plural end in -a.
| Case | Singular | Plural |
|---|---|---|
| Nom. | flūmen | flūmina |
| Gen. | flūminis | flūminum |
| Dat. | flūminī | flūminibus |
| Acc. | flūmen | flūmina |
| Abl. | flūmine | flūminibus |
Quick check
Tap an answer to check it.
What is the base of mīles, mīlitis?
- The base comes from the genitive, not the nominative
Show answer
mīlit-. Drop -is from the genitive: mīlit-.
Why it matters
Many of the most common words are third declension: rēx, mīles, pater, māter, frāter, homō, tempus, nōmen. Once you can read the genitive, the rest follows one set of endings.
Worked example
- Rēx mīlitēs laudat. → The king praises the soldiers.
- Pater puerōrum est mīles. → The boys' father is a soldier.
- Lēgātus legiōnem ad flūmen dūxit. → The lieutenant led the legion to the river.
Common mistake
Using the nominative as the base: wrong: mīlem, wrong: flūmenis. The nominative is often changed (rēg-s → rēx, mīlit-s → mīles). Always build from the genitive: mīlitem, flūminis.
Key terms
- rēx, rēgis, m.
- king
- mīles, mīlitis, m.
- soldier
- pater, patris, m.
- father
- māter, mātris, f.
- mother
- legiō, legiōnis, f.
- legion
- flūmen, flūminis, n.
- river
- tempus, temporis, n.
- time
Practise the key terms
Tap a card to turn it over. 7 cards.
| Front | Back |
|---|---|
| rēx, rēgis, m. | king |
| mīles, mīlitis, m. | soldier |
| pater, patris, m. | father |
| māter, mātris, f. | mother |
| legiō, legiōnis, f. | legion |
| flūmen, flūminis, n. | river |
| tempus, temporis, n. | time |
Practice
Recognition drill
Pick the right answer, as fast as you can.
All pairs
Tap a card to turn it over. 6 cards.
| Front | Back |
|---|---|
| rēx | rēgis |
| mīles | mīlitis |
| legiō | legiōnis |
| pater | patris |
| flūmen | flūminis |
| tempus | temporis |
Quick quiz
Tap an answer to check it.
Accusative singular of legiō
- Build on the base legiōn-, from the genitive
Show answer
legiōnem. Base legiōn- + -em.
Nominative plural of tempus
- Neuters end in -a in the nominative plural
Show answer
tempora. Neuter: tempor- + -a.
mātribus is …
- The genitive plural is mātrum
Show answer
dative or ablative plural. -ibus: dative and ablative plural.
Practise speaking
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You are a patient Latin tutor. Use the classical pronunciation only, never the Church one: c is always k, g is always hard, v sounds like w, ae like the ai in aisle, and long vowels are held longer. Speak slowly. Use only these Latin words: rēx, mīles, pater, māter, legiō, flūmen, tempus, laudat, videt. Give me a noun and a case in English (for example 'the kings, accusative' or 'of the river'), and I will say the Latin form aloud. Do 10 forms. After each answer, tell me what kind of mistake I made, if any, and let me try again, then tell me one thing to improve. Keep every reply under 2 sentences. If I need a name or a town, I will make one up. Speak English except for the Latin itself.
Listen too. Listen to native speakers before and after: see the free listening and shadowing links.
Good to know. AI feedback on pronunciation is hit and miss, so check yourself against native recordings. This course teaches the classical pronunciation (see lesson 1); AI voices may mix it with the Church (Italian-style) one, so ask for classical and check against lesson 1. Don't share personal details: use a made-up name and town.
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In short
- Learn every third-declension noun with its genitive; drop -is for the base.
- Masc./fem.: -s or none, -is, -ī, -em, -e; -ēs, -um, -ibus, -ēs, -ibus.
- Neuter: nominative = accusative; plural -a.
- The nominative often hides the base: rēx (rēg-), mīles (mīlit-), flūmen (flūmin-).
Mastery check
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Check yourself
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Give the dative plural of mīles.
Show answer
mīlitibus.
Translate Pater mīlitum est rēx.
Show answer
The father of the soldiers is the king.
Why can't you build the forms of flūmen from the nominative?
Show answer
The base is flūmin-, which only the genitive flūminis shows.
Further reading
- D'Ooge, Latin for Beginners, Lessons XXXIX–XLII, §§ 230–240. Public domain; Project Gutenberg.
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