Second Declension

[Spirithound]

Singular
.......Masculine.....................Neu ter
NOM: populus.....puer.......ager......donum
GEN: populi......pueri......agri......doni
DAT: populo......puero......agro......dono
ACC: populum.....puerum.....agrum.....donum
ABL: populo......puero......agro......dono

Plural
NOM: populi......pueri......agri......dona
GEN: populorum...puerorum...agrorum...donorum
DAT: populis.....pueris.....agris.....donis
ACC: populos.....pueros.....agros.....dona
ABL: populis.....pueris.....agris.....donis

"populus", "puer", and "ager" are all masculine 2nd declension nouns, differing slightly in the nominative singular. In "populus", the '-us' ending is a proper case marker; remove it and replace it with another ending for another case.

When there is no ending, as in "puer" and "ager", it is a little more tricky, as you need to decide whether a vowel needs to be dropped. I haven't done a proper analysis yet, but I suspect that when the two vowels are together, called a diphthong, you keep both vowels, but when the vowel is not connected to another vowel, it is deleted.

"donum" is a neuter 2nd declension noun. Notice how the accusative is the same form as the nominative in both singular and plural.

[zdon011]

Originally Posted by Spirithound

In "populus", the '-us' ending is a proper case marker; remove it and replace it with another ending for [every other] case.
When there is no ending, as in "puer" and "ager", it is a little more tricky, as you need to decide whether a vowel needs to be dropped...but I suspect that when the two vowels are together, called a diphthong, you keep both vowels, but when the vowel is not connected to another vowel, it is deleted.

You're not far off the mark. Here's what I was taught:

2nd Declension nouns ending in -er and -r are like 'populus', except in the nominative singular.

Most -er nouns drop the -e- of the nominative singular in other cases.
A few -er nouns keep the -e- in all cases.

We can usually tell that the -e- will be dropped, if it is dropped in a derivative English word, e.g.:

'magister, magistri'-->'magistrate'
'liber, libri,'------------->'library'
'ager, agri,'------------>'agriculture'

'puer, pueri'----------->'puerile'
'vesper, vesperi'----->'vespers.'

Pax vobiscum

[tee_eff_em]

Another exceptional 2nd declension word is vir, viri -- "Man; male human being".

Case	singular	English	plural	English
Nominative	vir	the man	viri	the men
Genitive	viri	of the man	virorum	of the men
Dative	viro	to/for the man	viris	to/for the men
Accusative	virum	toward the man	viros	toward the men
Ablative	viro	by the man	viris	by the men

tee

[floresco]

Originally Posted by tee_eff_em

Another exceptional 2nd declension word is vir, viri -- "Man; male human being".

I just learned this summer that there are second declension nouns that are exceptional in gender; i.e. feminine. An example is fagus "beech tree"