Coemptio forma matrimonii est.

Coemptio is in the nominative singular. In this sentence, it is the subject of est.

A good way to recognize this is:

• est = is (3rd person singular)
• so we expect a singular subject
• coemptio is the noun functioning as that subject

This is a common Latin sentence pattern:

• X Y est = X is Y

Here, Coemptio is the thing being talked about.

In Latin, after a form of esse (to be), both the subject and the predicate noun are often in the nominative.

So in:

• Coemptio forma matrimonii est

both:

• Coemptio = nominative
• forma = nominative

This is just like saying:

• Marcus agricola est = Marcus is a farmer

Both Marcus and agricola are nominative because agricola is a predicate nominative: it renames or identifies the subject.

Because matrimonii is genitive singular, not nominative or accusative.

The genitive often expresses of in English. So:

• forma matrimonii = a form of marriage

Here is the breakdown:

• matrimonium = marriage (dictionary form, nominative singular)
• matrimonii = of marriage (genitive singular)

A native English speaker often expects a preposition like of, but Latin can express that relationship just by changing the ending.

Because matrimonii is a genitive depending on forma.

So the structure is:

• Coemptio = subject
• forma matrimonii = predicate noun phrase
• est = verb

In other words:

• forma = form
• matrimonii = of marriage

Together they make one unit: a form of marriage.

This is very common in Latin. A noun in the genitive often attaches closely to another noun:

• porta urbis = the gate of the city
• amor patriae = love of country

Latin often puts the verb near the end, but it does not always have to.

So:

• Coemptio forma matrimonii est

is a very normal Latin word order, but Latin is more flexible than English because the endings show the grammatical roles.

You could also see:

• Coemptio est forma matrimonii

and it would mean the same thing.

The ending patterns matter more than word order does. Still, verb-final order is extremely common in Latin prose.

The basic meaning is the same.

The difference is mainly one of style, rhythm, or emphasis, not grammar. Latin speakers and writers can move words around more freely than English speakers can.

Very roughly:

• Coemptio forma matrimonii est feels like a straightforward statement with the verb saved for the end
• Coemptio est forma matrimonii may feel a bit more balanced to an English learner because the verb appears earlier

But both are correct and natural.

Classical Latin has no articles like English a, an, and the.

So forma matrimonii could be understood as:

• a form of marriage
• the form of marriage
• sometimes simply form of marriage

The context tells you which English article is best.

This is something English speakers often have to get used to: Latin leaves this unstated unless some other word makes it more specific.

Yes, grammatical gender matters in Latin, though in this sentence there is no adjective that has to agree with the nouns.

The nouns are:

• coemptio — feminine
• forma — feminine
• matrimonium — neuter, so matrimonii is neuter genitive singular

Gender matters because adjectives, pronouns, and some participles have to agree with the nouns they describe. Even though that is not the main issue in this sentence, it is useful to know the gender when learning vocabulary.

They come from different declensions:

• coemptio, coemptionis — 3rd declension
• forma, formae — 1st declension
• matrimonium, matrimonii — 2nd declension neuter

This is helpful because the endings make more sense when you know the declension:

• forma = nominative singular 1st declension
• matrimonii = genitive singular 2nd declension neuter
• coemptio = nominative singular 3rd declension

English speakers often assume similar-looking endings always belong to the same pattern, but Latin uses several declensions, so memorizing dictionary forms is important.

A common reconstructed Classical pronunciation would be roughly:

• ko-EMP-tee-oh FOR-ma ma-tree-MOH-nee-ee est

A few helpful notes:

• coe- begins with co-eh blending into koi/koe depending on how carefully it is pronounced
• ti before a vowel in Classical Latin is usually a real t sound, so coemptio is not like English co-emption with sh
• matrimonii contains two i vowels in sequence: matrimo-nii

If you are learning ecclesiastical pronunciation, some sounds may differ.

Yes. That is a very good way to think about the structure:

• Coemptio = subject
• est = is
• forma matrimonii = a form of marriage

So the grammar is basically:

• Subject + predicate nominative + verb

Even though the English translation may look simple, the Latin sentence is useful because it shows several important features at once:

• nominative subject
• predicate nominative after est
• genitive depending on another noun
• flexible word order
• no article

That makes it a good example sentence for beginners.