Ambō is sometimes decline to match its respective noun, like a fully-functional adjective, but otherwise remains fixed as ambō
Effectively, there is no rule. Both A&G and L&S present freeform variation between the two options.
In my opinion, A&G make too big a fuss over mixed i-stems, which are essentially a broad class of nouns that usually feature a genitive plural in -ium and might feature an accusative plural in -īs, but are otherwise regular third declension nouns.
Here are five of their six morphological classes, along with all the examples they offer. (I’m excluding 71.4 because it’s ridiculous that they’ve placed it there at all):
1. Nouns in (n.) -ēs, (g.) -is.
2. All monosyllable nominatives in -s or -x preceded by a consonant.
3. On the following monosyllable nominatives in -s or –x preceded by a vowel.
4. Polysyllable nominatives in -ns or -rs.
This does not apply to all present active participles!
5. Patrials (nouns denoting birth, class, abode) in -ās and -īs.
The (very much non-)Essential AG: 71-2
As A&G note, “The i-stem was confused by even the Romans themselves.” There are a variety of variations with this stem present in all three grammatical genders, making it incredibly difficult to organize the data except in broad patterns and rote memorization. To that effective, I’m going to design a series of posts on the i-stem declension.
In this section, we’ll introduce the i-stem as a morphological class, and discuss the declension of ‘regular’ masculine and feminine i-stem nouns.
First off, all i-stems are either pure or mixed.
Most pure i-stems are immediately identifiable by their lexical entry, because they feature parisyllabic (having the same number of syllables) nominative and genitive forms. This is true of masculine, feminine and neuter i-stem nouns. However, most masculine and feminine nouns also have nominative and genitive forms that are completely identical. Let’s take a look:
sitis, sitis (f.) thirst (declined only in the singular, for sensible reasons)
ignis, ignis (m.) fire
A few unique features to note:
As you can see, there aren’t many markers (just one) that guarantee any given noun is an i-stem noun. In fact, it would be possible to decline ignis in a way such that only it’s nominative singular and genitive plural gave any hint of the i-stem status.
With four nouns in particular (imber, rain; linter, skiff; ūter, wineskin; venter, belly) this problem is even more evidence because here even the nominative is lost as a distinctive feature. The only morphological form that demonstrates imber‘s i-stem status is its genitive plural imbrium.
So to review masculine and feminine i-stem declension: difficult, difficult, difficult. As we’ll see, the neuter declension isn’t much easier…
The essential AG: 66-7.
As A&G note, “The i-stem was confused by even the Romans themselves.” There are a variety of variations with this stem present in all three grammatical genders, making it incredibly difficult to organize the data except in broad patterns and rote memorization. To that effective, I’m going to design a series of posts on the i-stem declension.
The basic neuter i-stem declension takes the stem (mari-) and converts the final i- to an e- in the nominative and accusative singular.
mare, maris (n.) sea
sedīle, sedīlis (n.) seat
(photo credit: Wiktionary).
In this basic output, the neuter i-stem is far more regular than its masculine and feminine counterparts:
These are all regularized and there are no exceptions…except for the majority of nouns in the neuter i-stem declension, which don’t decline like this at all. Most neuter i-stem nouns have a consonantal base in -al or -ar, which is retained in all morphological forms. This causes only one change: these forms are animal, animalis, and not *animale, animalis. Everything else remains the same.
tribūnal, tribūnālis (n.) judge’s platform
There’s one feature that Wiktionary fails to capture in this chat. The -a- at the end of the stem is short in the nominative and accusative singular, but along everywhere else (see my lexical entry above). This is true of all i-stem nouns ending in –al or -ar.
calcar, calcāris (n.): spur
(Here they got the -a- right. Go figure.)
There you have it! The neuter i-stem declension. It’s fairly regular; it merely entails a large quantity of regular rules.
The Essential AG: 68-9
The Romans referred to Jupiter, but also to Jove. How did this work?
The nominative, Iuppiter, is derived from the archaic vocative Iū and pater (the word is a ‘syntactic compound’). The rest of the cases are derived from the stem Iov-, which A&G identify as related to the Greek Ζεύς through the PIE root *dyew. We can imagine that ‘Iovis‘ could serve a nominative, but the go-to nominative is definitely Iuppiter (or Iupiter).
(photo credit: Wiktionary)
You might be curious about why there’s a plural declension. Statues of Jove were also called ‘Joves.’
The Essential AG: 79, 79b, 100, 266c
A&G define the vocative as “the case of Direct Address.” (35f)
Generally speaking, the vocative and the nominative are the same.
However, in certain nouns of the second declension (those with nominative -us or -ius) have two exceptional variations. All nouns in -us feature an -e in the vocative (mūrus…mūre). Those ending in -ius (Vergilius, fīlius, genius, etc.) take a vocative -ī (Vergilī, filī, genī).
That’s how it stands for nouns. There’s a slight variation in policy for adjectives, though luckily the same general rule (same as the nominative) holds true for all but the second declension (bonus…bone). However, the one catch is that adjectives ending in -ius change to -ie and not -ī. Therefore, when calling to a Spartan son, we might say O fīlī Lacedaemonie! (not *Lacedaemonī).
If anyone has a better understanding of vocative plurals, which I assume are all identical to their nominative forms, feel free to say more in the comments below. A&G are totally silent on this issue, which I assume signals that listing the vocatives would be redundant (with respect to the nominatives).
The Essential AG: 38a
The relative pronoun is used within a complex sentence to refer to some antecedent in an earlier clause. In Latin, the relative pronoun is decline, and should fit syntactically with its own clause, rather than the case of its antecedent. For instance:
The antecedent (nominative) does not align with the relative pronoun (accusative). Also, note how easily Latin shifts and embeds a relative clause:
These are both acceptable (albeit irregular/poetic) alternatives to the sentence above.
The relatives are declined as follows–
The Essential AG: 147
There are four central aspects to the Latin numeral:
The numerals 11-19 are indeclinable:
The numerals 20-100 are expressed as follows; bases of ten do not decline:
To achieve a number like 85, the Romans have two preferred methods:
The hundreds above 100 decline as adjectives like bonus, bona, bonum
Mille is an odd bird: it’s indeclinable as a singular (mīlle mīlitēs) but declines as a neuter plural (tria mīlia mīlitum)
To express numbers with three digits or more:
If et appears anywhere, it appears only between the two highest demoninations:
Summary of First and Second Declension -ro/-ra Stem Adjectives
Summary of Declension
Adjectives with the stem ro- are of two classes: (i) those preceded by e [viz. ero-] and (ii) those preceded by a consonant [viz. gro-, bro-, fro-, etc.]
All members of both classes are first/second declension adjectives
Adjectives in Class (i) [ e-class ]
Adjectives in Class (ii) [ consonant-class ]
Exceptional Variants
The Essential AG : 111, 112
Famous Phrase : aegri somnia (a sick man’s dreams = trouble sleep)
[Horace, Ars Poetica 7—but presently popular with hipster and counterculture groups]
Latin for Addicts 