Magistra, quae forte adest, dicit bonum concentum non ex voce una, sed ex multis vocibus oriri.

The sentence breaks down like this:

• Magistra = the teacher, the subject
• quae forte adest = who happens to be present, a relative clause describing magistra
• dicit = says
• bonum concentum ... oriri = that a good harmony arises...
• non ex voce una, sed ex multis vocibus = not from one voice, but from many voices

So the overall structure is:

• The teacher, who happens to be present, says that a good harmony arises not from one voice but from many voices.

Quae is the feminine singular nominative form of the relative pronoun.

It refers back to magistra, which is:

• feminine
• singular
• nominative

So quae means who in the sense of the teacher, who...

It agrees with magistra in gender and number, and its case comes from its role inside the relative clause, where it is the subject of adest.

Here forte is an adverb meaning something like:

• by chance
• as it happens
• perhaps in some contexts

So quae forte adest means who happens to be present or who is there by chance.

A native English speaker might be tempted to connect forte with the musical term forte, but in Latin this word is unrelated in meaning here.

Adest comes from adsum, which literally means to be present, to be here, or to be at hand.

So:

• est = is
• adest = is present

Latin often uses adsum when the idea is not just existence, but actual presence in a place or situation.

So quae forte adest is more specific than just quae est.

It is best understood as nominative, the subject of dicit.

So:

• Magistra ... dicit = The teacher ... says

It is true that magistra could also be vocative in form, since first-declension nominative and vocative singular are usually identical. But here the sentence structure clearly makes it the subject, not a direct address.

Because this is an indirect statement after dicit.

Latin often expresses X says that Y happens with:

• a verb of saying/thinking/perceiving
• an accusative subject
• an infinitive

So in:

• dicit bonum concentum ... oriri

the phrase bonum concentum is the subject of oriri, but in indirect statement that subject goes into the accusative.

In English we say:

• she says that a good harmony arises

In Latin, literally:

• she says a good harmony to arise

The pattern is:

• dicit = she says
• bonum concentum = a good harmony, accusative subject
• oriri = to arise, infinitive

So Latin uses accusative + infinitive where English usually uses that + finite verb.

You can think of it like this:

• Magistra dicit = The teacher says
• bonum concentum oriri = that a good harmony arises

This is one of the most common constructions in Latin, so it is worth learning well.

Because after dicit in indirect statement, Latin uses the infinitive, not a normal finite verb.

So:

• oritur = it arises
• oriri = to arise

In a direct statement, you might have:

• Bonus concentus oritur ex multis vocibus = A good harmony arises from many voices

But after dicit, Latin changes that into indirect statement:

• dicit bonum concentum ex multis vocibus oriri

Oriri is the infinitive of orior, a deponent verb.

A deponent verb:

• looks passive in form
• but has an active meaning

So although oriri has a form that looks passive, it means to arise, to come forth, to originate.

Its basic idea here is to arise from or to come from.

Because they follow ex, and ex takes the ablative.

So:

• ex voce una = from one voice
• ex multis vocibus = from many voices

The forms are:

• voce = ablative singular of vox
• vocibus = ablative plural of vox

This is a straightforward prepositional use of the ablative.

The difference is just singular versus plural:

• voce una = from one voice
• multis vocibus = from many voices

The noun vox is third declension:

• nominative singular: vox
• ablative singular: voce
• ablative plural: vocibus

The adjectives agree with the noun:

• una agrees with voce
• multis agrees with vocibus

Latin word order is more flexible than English word order.

So both of these are possible in principle:

• ex una voce
• ex voce una

Here ex voce una may slightly emphasize one single voice by placing una after the noun.

English speakers often expect adjective + noun order, but Latin can place adjectives before or after the noun for style, rhythm, or emphasis.

This is a very common Latin pairing meaning:

• not ... but ...

So:

• non ex voce una, sed ex multis vocibus
• not from one voice, but from many voices

It sets up a contrast very clearly.

Here concentus means something like:

• harmony
• concord of sound
• musical blending

The form concentum is the accusative singular.

A learner might wonder whether it means a literal concert, but in this sentence the sense is more like harmonious sound produced by several voices together.

Because of the indirect statement.

If this were the subject of a normal finite verb, you would expect nominative:

• bonus concentus oritur = a good harmony arises

But after dicit, the subject of the infinitive goes into the accusative:

• bonum concentum oriri

So the adjective changes too:

• nominative: bonus concentus
• accusative: bonum concentum

It can suggest both, depending on context.

Here ex means from in the sense of arising out of or coming from. It expresses source or origin:

• a good harmony arises from many voices

So the idea is that harmony is produced by the combination of many voices, not by a single one.

Yes.

The core sentence is:

• Magistra dicit bonum concentum non ex voce una, sed ex multis vocibus oriri.

The relative clause quae forte adest simply adds extra information about the teacher.

It is a descriptive insertion, not something required for the sentence to work grammatically.