Duodeviginti tabellae in capsa sunt, et puella dicit se duodeviginti litteras heri scripsisse.

Because tabellae is the nominative plural, and it is the subject of sunt.

In the first clause:

Duodeviginti tabellae in capsa sunt

the thing that are in the box is the eighteen tablets, so tabellae must be nominative.

If Latin used tabellas, that would be accusative plural, which is usually used for a direct object, not for the subject of sunt.

Because in with the ablative usually shows location: in, on, inside.

So:

• in capsa = in the box

If Latin were showing motion into the box, it would normally use in with the accusative instead.

A learner often remembers it this way:

• in + ablative = where?
• in + accusative = to where?

Here the tablets are already in the box, so the ablative is used.

Duodeviginti means eighteen.

It is formed in an old Latin way that literally means something like two from twenty:

• duo de viginti → duodeviginti

Latin often forms 18 and 19 this way:

• duodeviginti = 18
• undeviginti = 19

So instead of building upward from ten, Latin sometimes counts backward from twenty.

Because duodeviginti is an indeclinable numeral. That means its form does not change for case, gender, or number.

So Latin uses the same form in both places:

• duodeviginti tabellae
• duodeviginti litteras

The nouns change case as needed, but duodeviginti stays the same.

Because Latin commonly uses an indirect statement after verbs of saying, thinking, knowing, perceiving, and similar verbs.

After dicit (she says), Latin does not usually say that she wrote with a separate that-clause the way English does. Instead it uses:

• an accusative subject
• plus an infinitive

So:

• puella dicit se ... scripsisse

literally looks like:

• the girl says herself to have written...

but in natural English it means:

• the girl says that she wrote...

This is one of the most important Latin constructions to learn.

Se is the accusative reflexive pronoun, and in this sentence it is the subject of the infinitive in the indirect statement.

So in:

puella dicit se duodeviginti litteras heri scripsisse

se refers back to puella. In other words, it means herself, but in English we usually translate it simply as she in this construction:

• The girl says that she wrote eighteen letters yesterday.

Latin uses se because the subject of the reported action is the same person as the subject of dicit.

Because the writing happened before the saying.

• dicit = she says / is saying
• scripsisse = to have written

In indirect statement, Latin often shows time relative to the main verb:

• present infinitive = action happening at the same time
• perfect infinitive = action happening earlier
• future infinitive = action happening later

Since she says now that she wrote the letters yesterday, the writing is earlier than the saying, so Latin uses the perfect active infinitive:

• scripsisse = to have written

It is the perfect active infinitive of scribo, scribere, scripsi, scriptum (write).

The perfect infinitive is usually formed from the perfect stem plus -isse:

• scrips-
  • -isse = scripsisse

So scripsisse means to have written.

This is the form Latin needs in the indirect statement after dicit.

Because litteras is the direct object of scripsisse.

She wrote what?

• duodeviginti litteras

So litteras must be in the accusative plural.

Compare:

• tabellae = nominative plural subject
• litteras = accusative plural object

That contrast is very typical in Latin.

Probably not. In a sentence like this, litterae usually means a letter or letters in the sense of written messages/correspondence, not alphabet letters.

So duodeviginti litteras scripsisse most naturally means:

• to have written eighteen letters

That fits well with heri (yesterday) and with the verb scribo.

Latin littera can mean a letter of the alphabet, but the plural litterae very often means a letter, an epistle, written communication, or even literature/learning depending on context.

They are two different nouns.

• tabellae = small tablets, often writing tablets or little boards
• litterae = letters, especially written messages

So the first clause talks about physical objects in the box:

• Eighteen tablets are in the box

The second clause talks about what the girl says she wrote:

• she wrote eighteen letters yesterday

A learner may notice that both are connected with writing, but they are not the same word and not the same thing.

Heri means yesterday, and it modifies scripsisse.

So the sense is:

• the girl says that she wrote eighteen letters yesterday

Latin word order is flexible, so heri can appear in different places without changing the basic meaning. Here it stands right before scripsisse, which makes good sense because it clearly goes with the act of writing.

Latin often places adverbs where they are useful for emphasis or clarity rather than following a fixed English-style order.

Because Latin has much freer word order than English, and verbs often come near the end of the clause.

So:

Duodeviginti tabellae in capsa sunt

is a very normal Latin arrangement.

Latin word order is not random, but it is not as rigid as English word order. End position is especially common for verbs, though many other orders are also possible.

Normally, no. In this kind of sentence, classical Latin usually prefers the accusative-and-infinitive construction rather than a that-clause.

English says:

• The girl says that she wrote...

Latin says:

• puella dicit se ... scripsisse

So when English speakers learn Latin, one of the biggest adjustments is getting used to the fact that Latin often expresses reported speech without a separate word meaning that.

In normal Latin, se in this kind of sentence refers back to the subject of the main clause, here puella.

So:

• puella dicit se... = the girl says that she...

If Latin wanted to refer to some other female person, it would usually use a different pronoun or wording, not se.

So in this sentence, se is naturally understood as referring to the girl herself.

Because the sentence states two related facts:

1. Duodeviginti tabellae in capsa sunt
2. puella dicit se duodeviginti litteras heri scripsisse

Et simply means and, joining the two statements.

A learner may also notice the neat repetition of duodeviginti in both clauses. That repetition helps connect the ideas stylistically:

• eighteen tablets
• eighteen letters

Yes: it is a very natural Latin order for an indirect statement.

You can think of it in pieces:

• puella dicit = main clause
• se = accusative subject of the indirect statement
• duodeviginti litteras = object
• heri = adverb
• scripsisse = infinitive, often saved for the end

Latin often places the infinitive at or near the end of the indirect statement, so this order is quite typical and helps the whole reported idea build toward the final verb.