"Two boys and two girls study."
Translation:Duo pueri et duae puellae student.
This is what I understand about chiasmus:
it requires two sets or pairs of words, of any type, arranged such that one pair is "surrounding" and the other "is in the middle", for an ABBA pattern.
In our simple sentence here, we have 2 nouns in the nomin. plural (pueri, puellae), and 2 adjs., one for each noun (duo, duae).
We can "pair up" the four words in an artful way:
chiasmus is having 2 on the outside (duo ... duae) and 2 in the middle (pueri, puellae), linked either by et or a -que: Duo pueri puellaeque duae. If A = adjective and B = noun, we've done: A . B . B . A
(In making sense of the phrase, notice that we "pair" them differently: in sense, duo pueri = 2 boys, and duae puellae = 2 girls. To make the chiasmus, we were thinking of their other, formal qualities: which ones are nouns, which are adjectives.)
A well-known chiasmus in English is the witches' "Fair is foul, and foul is fair," from Macbeth. (fair = A, foul = B)
It's not only poetic, because I know some examples from Caesar, and I'm sure Cicero and other writers of artful prose used it all the time.
In Book 4 of De Bello Gallico, Caesar reports that the Britons figured out that he had brought only a very few men to Britannia, hence that an attack on the Romans might be successful: " ... cum equites et naves et frumentum Romanis deesse intellegerent et paucitatem militum ex castrorum exiguitate cognoscerent, ..." (4. 30). "When they learned that cavalry and ships were lacking for the Romans, and when they recognized _ the small number of soldiers from the small size of the camp, _ ..."
The chiasmus is in the ABBA words, paucitatem militum (ex) castrorum exiguitate . He's gone out of his way to make the 2 genitive plural forms (militum, of soldiers; castrorum, of the camp) 'abut' each other, and he's stationed the two abstract 'size & bigness' words (paucitatem, accus., and exiguitate, abl. object of ex) on the 'outside' of the genitives, 'surrounding' them.
Most numbers are indeclinable: there's only one form for the number, and it never changes.
This is true for 4 on up--with the exception that PLURAL hundreds and PLURAL thousands are adjectives.
So, to be clear: we're noticing that "two" has distinct masc and fem forms; in fact, it has different forms for all 3 genders, and for the five cases.
The shouts OF two girls: clāmōrēs duārum puellārum versus the shouts OF two soldiers: clāmōrēs duōrum mīlitum (and the rumbles OF two vehicles: murmura duōrum vehiculōrum ).
ONE is gendered: ūnus, ūna, ūnum are the 3 nominative singular forms, M / F/ N respectively. There are 5 different cases (nom, gen, dat, acc, abl).
THREE is also gendered: trēs, trēs, tria , for the nominative plurals M/F/N respectively. (This word follows a 3rd declension pattern.)
But FOUR = quattuor . It only has the one form, that never changes. "I see four boys": quattuor puerōs videō". "Four boys are shouting": quattuor puerī clāmant .
A hundred = centum (indeclinable). But you could lead five hundred soldiers into battle: quīngentōs mīlitēs in pugnam dūcis .
A thousand = mīlle, indeclinable. But Catullus can say, "Give me a hundred kisses, then a thousand; then a second hundred, and a second thousand . ... Then, when we have made many thousands" : and the "many thousands" are multa mīlia (mīlia, mīlium, n. pl., thousands--3rd decl.).
We could think that the English word "student" is from the Latin conjugation "student", but it's not, it's from "estudiant" (old form for étudiant).
The fact the English looks like the Latin conjugation is a pure coincidence. A funny coincidence.
Be advised that studeō, studēre is a second conjugation verb, so it retains its long -ē- in front of -s, -mus and -tis, unlike third conjugation verbs which have a short -ere, which causes the -e- to change to short -i- in front of -s, -t, -mus and -tis, and short -u- in front of -nt.