Pater miratur quantus imber tam subito ceciderit.

Because miratur comes from miror, mirari, a deponent verb.

Deponent verbs:

• have passive forms
• but active meanings

So miratur is morphologically passive in form, but it means he wonders, he is amazed, or he marvels.

In this sentence, pater miratur means the father wonders / is amazed.

Pater is nominative singular.

Its job is to be the subject of miratur:

• pater = the father
• miratur = wonders

So pater miratur = the father wonders.

Here quantus introduces an indirect question and means how great or how much.

So:

• quantus imber = how great a rainfall / how much rain

It is not just a descriptive adjective here. It is asking about the degree or extent of the rain.

This is a very common Latin pattern:

• rogat quantus sit = he asks how great it is
• miratur quantus sit = he wonders how great it is

Because quantus must agree with imber.

Imber is:

• masculine
• singular
• nominative

So quantus is also:

• masculine
• singular
• nominative

That is why we get quantus imber.

Yes. Imber is nominative singular, and it is the subject of ceciderit.

So inside the indirect question:

• quantus imber tam subito ceciderit means
• how great a rain / how much rain fell so suddenly

Even though imber comes earlier in the clause, it is still the thing that fell.

Because it is in an indirect question.

Latin normally uses the subjunctive in indirect questions after verbs like:

• ask
• know
• wonder
• see
• find out

Since miratur means wonders, the clause introduced by quantus is an indirect question, so the verb is subjunctive:

• direct question: quantus imber cecidit? = how much rain fell?
• indirect question: pater miratur quantus imber ceciderit = the father wonders how much rain fell

Ceciderit is 3rd person singular perfect subjunctive active of cado, cadere, cecidi.

Breaking it down:

• verb: cado = fall
• perfect stem: cecid-
• ending: -erit here gives the perfect subjunctive, 3rd singular

So ceciderit means something like:

• fell
• has fallen

In this sentence, it refers to an action completed before or by the time of the father’s wondering.

Because cecidit is indicative, while ceciderit is subjunctive.

Latin requires the subjunctive in this indirect question, so:

• cecidit would fit a direct statement or direct question
• ceciderit fits the dependent question after miratur

Compare:

• quantus imber cecidit? = how much rain fell?
• miratur quantus imber ceciderit = he wonders how much rain fell

Because the falling of the rain is viewed as a completed event.

The father is wondering about something that has already happened:

• the rain has fallen / fell
• now he is reacting to it

So Latin uses the perfect subjunctive to show prior or completed action within the indirect question.

Tam is an adverb meaning so. Subito is an adverb meaning suddenly.

Together:

• tam subito = so suddenly

Here tam intensifies subito.

So the phrase describes how the rain fell:

• it fell so suddenly

Here it is functioning as an adverb, meaning suddenly.

Latin often uses forms like subito adverbially. In this sentence it modifies ceciderit:

• ceciderit = fell / has fallen
• tam subito ceciderit = fell so suddenly

So it is telling us in what manner the rain fell.

Either can work, depending on how naturally you want to express it in English.

Literally:

• quantus imber = how great a rain

More idiomatically in English:

• how much rain
• what a heavy rain
• how great a downpour

A learner should notice that Latin can use imber where English might prefer rainfall, rain, or downpour.

The sentence is:

• Pater = subject of the main verb
• miratur = main verb
• quantus imber tam subito ceciderit = indirect question

This is a very normal Latin arrangement:

1. main clause
2. dependent clause

Inside the dependent clause, the order is also fairly natural:

• quantus imber first, because that is the thing being wondered about
• tam subito adds description
• ceciderit comes at the end, which is very common in Latin subordinate clauses

So the order is not strange; it is actually quite typical Latin.

Yes.

Miror can express:

• intellectual wondering: he wonders
• emotional astonishment: he is amazed / marvels

Both ideas fit well in this sentence. The exact English choice depends on context:

• if the focus is on a question in his mind, wonders
• if the focus is on surprise, is amazed

Latin often allows both shades of meaning at once.

It is best understood as an indirect question.

That is because it depends on miratur, and the subjunctive ceciderit matches the normal pattern for indirect questions.

So the sense is:

• the father wonders how great the rainfall was

It may also carry an exclamatory flavor in English, but grammatically in Latin this is an indirect question.

A learner would usually identify them like this:

• pater from pater, patris = father
• miratur from miror, mirari, miratus sum = wonder at, marvel at
• quantus from quantus, -a, -um = how great, how much
• imber from imber, imbris = rain, rainstorm
• tam = so
• subito = suddenly
• ceciderit from cado, cadere, cecidi, casum = fall

Recognizing ceciderit can be tricky because its perfect stem cecid- is not obvious unless you already know the principal parts of cado.