In indice commentarii magistra nomina auctorum scribit.

Because in takes the ablative when it means in/on/at a place where something is located. Here the idea is location, not motion, so Latin uses in + ablative.

The noun is index, indicis. Its ablative singular is indice. So in indice means in the index.

Yes. In can take either:

• ablative for location: in indice = in the index
• accusative for motion into: for example, in indicem = into the index

So the case after in tells you whether Latin means being somewhere or moving into somewhere.

Here commentarii is genitive singular, meaning of the notebook/commentary.

The dictionary form is commentarius. Its genitive singular is commentarii (often written with macrons as commentariī). The double i happens because the stem ends in -i- and the genitive singular ending is another -i.

This form can look confusing, because commentarii can also be nominative plural in other contexts. In this sentence, though, it makes sense as genitive singular: in indice commentarii = in the index of the notebook/commentary.

Magistra is nominative singular, which is the case normally used for the subject. Also, the verb scribit is third person singular, so it matches a singular subject.

So magistra is the one doing the writing.

Nomina is accusative plural. It is the direct object of scribit, so it tells you what the teacher writes.

Its dictionary form is nomen, nominis, a third-declension neuter noun. A very important neuter rule is:

• nominative plural = accusative plural

So nomina can be either nominative plural or accusative plural depending on context. Here it is accusative plural because it is the object of scribit.

Auctorum is genitive plural from auctor, auctoris. The genitive here shows possession or relationship: the names of the authors.

So:

• nomina = names
• auctorum = of the authors

Together, nomina auctorum means the authors' names or the names of the authors.

Scribit is:

• present tense
• indicative mood
• active voice
• third person singular

So it means she writes, he writes, or sometimes is writing, depending on context. Since the subject is magistra, it means she writes.

Latin often leaves out subject pronouns because the verb ending already tells you the person and number.

In scribit, the ending -it tells you it is third person singular: he/she/it writes. Because magistra is present, there is no need to add a separate pronoun.

Latin does not have definite or indefinite articles like English the, a, or an.

So a noun like magistra can mean:

• teacher
• a teacher
• the teacher

Which one is best depends on context and the translation you have already been given.

Latin word order is much more flexible than English word order because the endings show what each word is doing.

This sentence has a very natural Latin order:

• In indice commentarii = setting/place first
• magistra = subject
• nomina auctorum = object phrase
• scribit = verb at the end

English relies heavily on word order, but Latin relies much more on case endings.

A good habit is to learn each word in its dictionary form:

• index, indicis = index
• commentarius, commentarii = notebook/commentary
• magistra, magistrae = female teacher
• nomen, nominis = name
• auctor, auctoris = author
• scribo, scribere, scripsi, scriptum = write

Learning these forms helps you recognize why the sentence uses indice, commentarii, nomina, and auctorum instead of the basic dictionary forms.