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Latin for Duolingo: 3rd Declension, Lesson 1


This is the latest in the series of Latin lessons for those waiting to see Latin come to the incubator. For a guide to previous lessons and a classified vocabulary list, be sure to check out these links:
- Directory of Lessons
- Classified Vocabulary List
- Memrise course for vocabulary
- Memrise course with sentences
- Previous lesson: 2nd Declension, Lesson 4

New Grammar
This is going to be a bit involved – if you just want to jump to the sentences and save grammar study for later, go ahead and scroll down.

Latin nouns are classified into 5 different groups, known as declensions. If you’ve followed thus far, we’ve covered the first and second declensions of nouns (and some adjectives). Learning the sets of case endings within each declension is essential to being able to use nouns accurately in Latin sentences. There are five cases in general use for each declension. This week, we’ll start the process of mastering the 3rd declension. Bear with me this lesson, because the 3rd declension is fairly complex and there are several rules that need to be laid out. Don’t be surprised if it takes several repeats through the vocabulary and sentences to understand some of these concepts.

3rd declension nouns are classified by their genitive singular, which ends in -is. The gen. s. also gives the stem of the noun, and there is sometimes considerable variation between the nominative and the genitive. For example, “homo, hominis”= man. The stem is “homin-“ and all other forms will follow the form of the stem, not the nominative. Nominatives have no regular ending in the 3rd declension: the --- in the case table basically means “anything goes.”

Gender rules ... actually, more like guidelines. All 3 genders occur in the 3rd declension. There is one set of endings that works for masculine or feminine nouns, and one set for neuter nouns. The differences in gender endings occur in the nominative and accusative forms; all other forms are identical regardless of gender. The first rule and the only one without exceptions is called the “natural gender” rule. Nouns naming male or female persons always are the gender of the person named. “Soror, sororis (f.) = sister” or “frater, fratris (m.) = brother.” Some nouns that can be either masculine or feminine are listed as “common” gender: “canis, canis (c.) = dog” or “hostis, hostis (c.) = enemy.” Most of these nouns are assumed to be masculine unless you have a specific sign otherwise like a feminine modifier (e.g. parvae canes = the small female dogs). Then, to make an educated guess about the gender of other 3rd declension nouns, I suggest the “SOX, ERROR and LANCET” rules. Look at the final letter of the nom. s. If it is S, O, or X the gender is usually feminine (because the women have to pick up all the SOX); if it is ER, R, or OR it is usually masculine (because, you guessed it, men make all the mistakes); and if it is L,A,N,C,E, or T it is usually neuter, because a lancet is just a thing (neither masc. nor fem.) that doctors use. These “rules” have plenty of exceptions, but cover most of the 3rd declension nouns that aren’t already covered by the Natural Gender Rule. Oh yes, there are also quite a few neuter nouns than end in –us in the nom. s. and –ris in the gen. s. Because it’s all so confusing, I’ll list the gender in the vocabulary listings as well.

I-stems – Some 3rd declension nouns have an extra -i- added before the gen. pl. ending. These will be listed in the vocabulary this way: “pars, partis, partium (f.) = part.” Since we aren’t going into the genitives other than to identify the stem this lesson, I’ll save the gory details for a future lesson! We’ll just have an assortment of regular nouns of all 3 genders this week.

We will focus on the nominatives and accusatives this lesson. Remember, nominative is for subject or predicate nouns, and accusative is for direct objects. Study the highlighted sections of the case table below for these, and note the differences between m./f. and n. Let’s take “pater, patris” as our example for m/f nouns, and “flumen, fluminis” as an example for neuter. Nom. s. = pater; acc. s. = patrem. Nom. pl. and acc. pl. both = patres. Remember that for neuter nouns, nom. and acc. are the same. So: nom. and acc. s. = flumen. Nom. and acc. pl. = flumina. The spelling change that occurs in the genitive s. applies to all other cases except nom. s. for m./f. nouns, and to all cases except nom. and acc. s. for neuter nouns.

case name | sing. | pl. | typical use
nominative (m./f.) | --- | -es | subject or predicate noun
nominative (n.) | --- | -(i)a | “
genitive | -is | -(i)um | possession, the “of” case
dative | -i | -ibus | indirect object, the “to/for” case
accusative (m.) | -em | -es | direct object (also some objects of preps.)
accusative (n.) | --- | -(i)a | “
ablative | -e | -ibus | objects of prepositions, etc. “by/with/from” case

New Vocabulary
canis, canis (c.) = dog
flumen, fluminis (n.) = river
frater, fratris (m.) = brother
homo, hominis (m.) = man, human
lex, legis (f.) = law
lux, lucis (f.) = light
mater, matris (f.) = mother
miles, militis (m.) = soldier
nomen, nominis (n.) = name
pater, patris (m.) = father
rex, regis (m.) = king
soror, sororis (f.) = sister

New Sentences
Marcus est homo. = Marcus is a man.
Marcus et Gaius sunt homines. = Marcus and Gaius are men.
Hominem vides. = You see the man.
Hominem, Marcum, videtis. = You (all) see the man, Marcus. n.b. this is an appositive; Marcus gives us a little more specific information about the man, so note that it is in the same accusative case. You see the man, (who is) Marcus.
Soror mea homines, Marcum et Gaium, videt. = My sister sees the men, Marcus and Gaius.
Lux est bona. = The light is good.
Marcus miles est. = Marcus is a soldier.
Homines sunt milites. = The men are soldiers.
Homo militem videt. = The man sees the soldier.
Nomen amici mei in diario video. = I see my friend’s name in the newspaper.
Nomina amicorum meorum in diario video. = I see my friends’ names in the newspaper.
Canis lucem videt. = The dog sees the light.
Rex multas leges in libro legit. = The king reads many laws in the book.
Mater tua et pater tuus in Italiā habitant. = Your mother and your father live in Italy.
Sororem tuam, Luciam, videt. = He sees your sister Lucia.
Patres puerorum sunt fratres. = The fathers of the boys are brothers.
Sunt multa flumina in Galliā. = There are many rivers in Gaul.
Flumen Mississippi in Americā est. = The Mississippi River is in America.
Cave canem! = Beware of the dog!

Well, this has been a long and complex lesson, and I hope it hasn’t been too overwhelming. Sorting out the 3rd declension nouns is challenging, but the remaining two declensions will be easy by comparison. I’ll try to respond to questions about this week’s material if you post them below. I will also be updating the classified vocabulary list, where you can study 3rd declension nouns classified by a) m./f. regular, b) n. regular, c) m./f. i-stem, and d) n. i-stem. You may find it helpful to study the groups of nouns together in this way. Excelsior! (Ever higher!)

Go to the next lesson: 3rd Declension, Lesson 2

July 7, 2015



I haven't had the time lately to look at these lessons, but I just wanted to chime in and say thank you! I plan on returning to them at a later point. :)


Remember, masculine/feminine i-stems have the i in only the gen. pl. Neuter i-stems have it throughout the declension. Good work!


Right, I am studying up on the neuter i-stems now. The books I'm most familiar with don't emphasize them at all. It's tricky striking the balance between "just enough grammar" and "information overload!"


Yeah, I agree. I took a year of Latin in middle school. On the first day of high school Latin II as a freshman (it was a sophomore class), they were using i-stems. I was so confused! I had went an entire year without them and hadn't missed them!


Thank you for these lessons and to zsocio for bringing them to life in memrise.


Libenter! Quoque gratias tibi!


OMG, I have busted my ass off knowing "Hominem, Marcum, videtis." here should be in vocative then I saw this discussion post. Marcus is actually the man that is seen. I really should read this thoroughly

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