3rd declension nouns are a big topic in Latin.
Below is a list of all the links in the FB group that have dealt with this.
https://www.facebook.com/groups/latinforstarters/permalink/429662662978341/
These nouns, like any other nouns, take endings but the most
the most important point to remember is that the endings are added to the stem
of the genitive case. That matters because the genitive case stem is very often
different from the nominative. The example shows this:
dux, ducis [3/m]: leader; commander
It is the second form listed i.e. dūcis that is the genitive
singular and you can see there is a change: dūx > dūcis. Before
endings are added, you create the stem by removing the genitive case ending
-is:
dūcis > dūc-; now you’re ready to go.
This post only deals with the singular forms:
Nominative: dux adest │ the leader is here / present
As soon as endings are added, see what happens:
Genitive: ducis epistula │ the leader’s letter
Dative: ducī epistulam dat │ he gives a letter to the
leader
Accusative: ducem occīdit │ he kills the leader
Ablative: cum duce meō sum │ I am with my leader
Sometimes, there is no change in which case the noun will
usually be listed as:
canis, -is [3m/f]: dog i.e. there is no stem change
However, most often you will come across nouns that do have
the stem change which is why it’s important to learn the noun along with its
genitive singular. There are patterns to this, but, espcially at the beginning,
it’s better simply to learn them as you meet them without thinking about any
patterns of change. Here are examples from the sentences:
No change in the stem:
sōl, -is [3/m]: sun
But …
color, colōris [3/m]: colour
lūx, lūcis [3/f]: light
vōx, vōcis [3/f]: voice
lēx, lēgis [3/f]: law
pēs, pedis [3/m]: foot
lapis, lapidis [3/m]: (precious) stone; jewel
cūstōs, cūstōdis[3/m]: guard
aestās, aestātis [3/f]: summer
mīles, mīlitis [3/m]: soldier
Now, there is a “trick” to this; it isn’t foolproof but it
can take you a long way in working out what those stem changes are. Many of
these nouns are in English and have been derived from declined forms of the
nouns i.e. the stem changes are there:
dux, duc¦is > Engl. ducal; duke
lūx, lūcis > Engl. Lucifer (the bringer of
light)
vōx, vōcis > Engl. vocal
lēx, lēgis > Engl. legal
cūstōs, cūstōdis > Engl. custodial
lapis, lapidis > Engl. lapidary (pertaining
to stones; a person who cuts stones)
mīles, mīlitis > Engl. military
pēs, pedis > Engl. pedestrian
And so, a good way of getting to grips with these as you go
along is to look at the genitive case ending and think of an English
derivative; the derivative may not have the same meaning but it will
show you what the change is. That won’t work with all of them, but it will work
with a lot of them, for example:
ars, artis [3/f]: skill; art
iūdex, iūdicis [3/m]: judge > Engl. judicial
nox, noctis [3/f]: night > Engl. nocturnal
rēx, rēgis [3/m]: king > Engl. regal
legiō, legiōnis [3/f]: legion
And if your family is getting on your nerves, you could drop
the /e/ and get rid of them all…
frāter, frātris [3/m]: brother > Engl. fratricide
māter, mātris [3/f]: mother > Engl. matricide
pater, patris [3/m]: father > Engl. patricide
