Avia tamen respondet cantum sine cithara pulchrum esse posse, sed chorum sine fidicine minus plenum videri.

The main finite verb is respondet.

After that, Latin gives two parallel indirect statements:

• cantum sine cithara pulchrum esse posse
• sed chorum sine fidicine minus plenum videri

So the sentence is built like this:

• Avia tamen respondet = the grandmother, however, replies
• cantum ... posse = that the song can be ...
• sed chorum ... videri = but that the chorus seems ...

Because Latin usually does not need a separate word for that in this kind of sentence.

After verbs of saying, thinking, knowing, perceiving, and replying, Latin often uses the accusative-and-infinitive construction instead of a that-clause.

So:

• respondet cantum ... posse
  means
• she replies that the song can ...

The idea of that is built into the construction itself.

In an indirect statement, the subject of the infinitive goes into the accusative.

So here:

• cantum is the subject of esse posse
• chorum is the subject of videri

Even though in English we would say the song and the chorus as subjects, Latin puts them in the accusative because they are subjects inside an indirect statement.

Because they are predicate adjectives agreeing with cantum and chorum.

In Latin, when an adjective describes the subject of an infinitive in indirect statement, it still agrees with that subject in:

• case
• number
• gender

So:

• cantum ... pulchrum = the song ... beautiful
• chorum ... plenum = the chorus ... full

Since cantum and chorum are accusative singular masculine, pulchrum and plenum are too.

Because posse means to be able, and it normally takes another infinitive with it.

Here:

• esse = to be
• posse = to be able

So:

• pulchrum esse posse literally means to be able to be beautiful
• in smoother English, can be beautiful

Both verbs are infinitives because the whole idea is inside an indirect statement after respondet.

Videri is the present passive infinitive of videre, but very often the passive of video means to seem or to appear.

So here:

• chorum ... videri = that the chorus seems ...

It does not mean that someone is literally seeing the chorus in this sentence. It is the common idiomatic meaning to seem.

Because sine always takes the ablative.

So:

• sine cithara = without a lyre/cithara
• sine fidicine = without a lyre-player / string-player

These are both ablative singular forms required by the preposition sine.

It is the ablative singular of fidicen, a third-declension noun.

That is why it does not look like a first- or second-declension noun. After sine, you need the ablative, so fidicen becomes fidicine.

A learner might expect something more familiar-looking, but this is just a normal third-declension form.

Tamen means however, nevertheless, or still.

Its placement is normal because tamen often comes near the beginning of its clause, frequently after the first word:

• Avia tamen respondet

That is a very common Latin pattern. English is usually less flexible about where however goes, but Latin is comfortable putting tamen in this early position.

Because Latin can express less + adjective by using minus with the positive form of the adjective.

So:

• minus plenum = less full

This is a straightforward way to express a lower degree of the quality. A learner may expect a single comparative form, but minus + adjective is a perfectly normal Latin way to say this.

Not really. It is fairly natural Latin word order, even though it does not match English word order closely.

Latin word order is more flexible because endings show the grammatical relationships. The sentence is arranged in a clear, balanced way:

• Avia tamen respondet
• cantum sine cithara pulchrum esse posse
• sed chorum sine fidicine minus plenum videri

The two halves after respondet are nicely parallel, which makes the contrast clearer:

• a song can still be beautiful without the instrument
• but a chorus seems less full without the player