Magistra dicit se arbitrari senatorem meliorem esse, si opinionem civium et mandata legis simul audiat.

Because Latin very often uses indirect statement after verbs like dicit (says), putat (thinks), scit (knows), and so on.

The usual pattern is:

• accusative subject
  • infinitive verb

So here:

• se arbitrari = that she thinks
• senatorem meliorem esse = that a senator is better

Latin does not need a separate word for that here.

Here se is the reflexive pronoun, and it refers back to magistra.

So:

• Magistra dicit se arbitrari...
  = The teacher says that she thinks...

It does not mean that she is doing something to herself. In this sentence, se is the subject of the infinitive arbitrari inside indirect statement.

A native English speaker may want to read se as an object, but here it is better understood as:

• she in reported speech, not herself in the emphatic English sense.

Because it is part of the indirect statement after dicit.

In direct form, you might have something like:

• Magistra arbitratur... = The teacher thinks...

But once that idea is reported after dicit, Latin changes it into an infinitive construction:

• Magistra dicit se arbitrari...

So arbitrari is infinitive because it belongs to what she says.

It looks passive, but it is actually deponent.

A deponent verb has passive forms but an active meaning. So:

• arbitror = I think / I judge
• arbitrari = to think / to judge

So se arbitrari means that she thinks, not that she is thought.

Because senatorem is the subject of another indirect statement:

• senatorem meliorem esse

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

So although in English we translate:

• that a senator is better

Latin literally uses:

• senatorem = accusative subject
• esse = infinitive verb

This is the same pattern as in:

• dicit puerum venire = he says that the boy is coming

Because meliorem is a comparative adjective and needs a form of to be here:

• senatorem meliorem esse = that a senator is better

Without esse, the clause would be incomplete.

This is a very common Latin pattern:

• bonum esse = to be good
• meliorem esse = to be better

Meliorem is the accusative singular masculine form of melior, meaning better.

Latin comparatives do not always need an explicit than phrase. Sometimes they simply mean:

• better
• a better sort of senator
• superior

So senatorem meliorem esse can mean that a senator is better even without saying exactly better than whom.

If Latin wanted to state the comparison explicitly, it could use:

• quam
  • same case, or
• the ablative of comparison

But here the comparison is left general.

This is one of the most natural questions to ask.

The short answer is: audiat is subjunctive because the si clause is presented within reported thought/speech, and Latin often uses the subjunctive in such subordinate clauses.

So the sentence is not just giving the narrator's flat statement; it is giving what the teacher says she thinks. Inside that reported idea, the conditional clause appears in the subjunctive:

• si ... audiat

Depending on context, this can feel like:

• if he listens
• if he should listen
• if he were to listen

So audiat gives the clause a less direct, more dependent or somewhat more ideal/hypothetical tone than plain audit would.

The understood subject is the same person as senatorem:

• the senator

Even though senatorem is accusative in the indirect statement, the idea is still:

• a senator is better if he listens...

Latin often leaves this subject unexpressed when it is clear from context.

So you can mentally supply:

• si ille audiat = if he listens / if he should listen

where he means the senator.

They are genitives depending on the nouns before them:

• opinionem civium = the opinion of the citizens
• mandata legis = the commands of the law

In English we often use of for this relationship, and Latin commonly uses the genitive.

So:

• civium tells whose opinion it is
• legis tells what the commands belong to or come from

Because the sentence is talking about:

• the opinion of the citizens as one collective body of opinion
• the commands of the law as multiple directives or requirements

Latin often uses a singular abstract noun where English might also use a singular:

• opinio = opinion / view

But mandata is naturally plural here because laws can contain several commands, orders, or instructions.

So the number is chosen for meaning, not because Latin requires the two nouns to match.

Latin has no articles like English a/an/the.

So senatorem can mean:

• a senator
• the senator

You decide from context.

In this sentence, English usually prefers a senator, because the statement sounds general:

• a senator is better if...

But Latin itself does not mark that difference with an article.

Simul means at the same time, together, or simultaneously.

Here it goes with audiat and suggests that the senator should listen to both things together:

• opinionem civium
• mandata legis

So the point is not to hear only one side, but to pay attention to both civic opinion and legal authority at once.

Yes. Very literally, that is exactly how the Latin works.

• opinionem = opinion
• civium = of the citizens
• et = and
• mandata = commands
• legis = of the law
• simul = at the same time
• audiat = he may listen / he should listen / he listens depending on how you bring the subjunctive into English

More natural English may say:

• if he listens both to the citizens' opinion and to the law's commands
• if he listens to public opinion and to the law at the same time

But the literal structure is still useful for understanding the Latin.