Princeps dicit bonos mores civitati magno auxilio esse.

A useful first step is:

• Princeps dicit = the leader says
• bonos mores civitati magno auxilio esse = that good morals are a great help to the state

So the sentence has:

1. a main clause: Princeps dicit
2. an indirect statement after dicit: bonos mores ... esse

A very literal unpacking is:

• The leader says
• good morals
• to be
• for a great help
• to the state

That sounds awkward in English, but it is normal Latin.

Because Latin usually puts indirect statements after verbs like dicit into the accusative + infinitive construction.

So instead of saying something like that good morals are... with a separate that-clause, Latin says:

• bonos mores = the subject of the reported statement, but in the accusative
• esse = to be

So bonos mores esse means that good morals are.

This is one of the most important Latin patterns to learn:

• verb of saying/thinking/perceiving
• then accusative subject + infinitive

In English, the subject of are stays in the nominative: good morals are.

In Latin indirect statement, the subject of the infinitive is put in the accusative instead. So the logical subject is still bonos mores, even though its case is accusative.

That is why learners often say:

• grammatical subject of the infinitive = accusative in Latin indirect statement
• logical meaning = still the thing doing the being

So bonos mores esse means good morals to be, or more naturally, that good morals are.

Mores is the plural of mos, moris.

Depending on context, mores can mean:

• customs
• ways
• character
• morals
• conduct

In this sentence, bonos mores most naturally means good morals or good character/behavior.

This is a very common Latin phrase.

This is a classic Latin construction called the double dative.

It combines:

• a dative of reference/advantage: civitati = for the state / to the state
• a dative of purpose: magno auxilio = for a great help

So:

• civitati magno auxilio esse

literally means:

• to be for a great help to the state

In natural English:

• to be a great help to the state
• to be of great help to the state

Because Latin is not using auxilium here as a normal predicate noun in the nominative or accusative. Instead, it is using the idiom esse + dative of purpose.

So Latin says:

• magno auxilio esse = to be for a great help

rather than:

• magnum auxilium esse

This dative idiom is extremely common with words like:

• auxilio = for a help
• curae = for a care
• saluti = for safety/salvation
• usui = for use

So magno auxilio is exactly what you should expect in this construction.

Civitati is dative singular of civitas, civitatis.

Here it means something like:

• to the state
• for the state
• to the community
• sometimes, depending on context, to the city

In this sentence, the state or the community is the most natural sense.

Each adjective matches the noun it describes in gender, number, and case.

So:

• bonos mores

  • bonos = masculine accusative plural
  • mores = masculine accusative plural

• magno auxilio

  • magno = neuter dative singular
  • auxilio = neuter dative singular

Even though the endings are different, the rule is the same in both phrases: the adjective agrees with its noun.

Princeps is the nominative singular subject of dicit.

It is a third-declension noun:

• nominative: princeps
• genitive: principis

Its basic meanings include:

• leader
• chief
• first man
• in some contexts, emperor

Here it is simply the one doing the saying.

The word order is flexible, but the cases tell you the grammar.

Latin puts esse at the end very often, especially in indirect statement. So this order is perfectly normal:

• Princeps dicit bonos mores civitati magno auxilio esse.

You could rearrange the sentence in other ways and still keep the same basic meaning, because:

• princeps is nominative
• bonos mores is accusative
• civitati and magno auxilio are dative
• esse is the infinitive

So Latin relies much more on endings than English does.

Not in the normal analysis of this sentence.

After dicit, Latin very commonly introduces reported speech with an accusative + infinitive construction. So when you see:

• dicit
• then an accusative phrase bonos mores
• then esse

the natural reading is:

• he says that good morals are...

So bonos mores belongs with esse, not as a separate direct object of dicit, but as the accusative subject of the indirect statement.