Pater dicit fas non esse amicum fallere.

Because after a verb of saying like dicit, Latin very often puts the reported statement into indirect statement.

The direct version would be:

Fas non est amicum fallere.

After dicit, the finite verb est changes to the infinitive esse:

Pater dicit fas non esse amicum fallere.

So esse is here because the father is saying that something is the case, not stating it directly in the narrator’s own voice.

Fas is a special indeclinable Latin word meaning something like:

• what is right
• what is permitted by divine or moral law
• what is proper

In the expression fas est or fas esse, it means it is right / it is permitted / it is morally acceptable.

So fas non esse amicum fallere means that deceiving a friend is not right.

A useful contrast is:

• fas = morally/divinely right
• nefas = morally/divinely wrong

No. Fas is not an adjective like bonus or malus.

It is an indeclinable noun, though in practice it often appears in the impersonal expression fas est. Because of that, learners sometimes first experience it almost like a fixed phrase meaning it is right.

So in this sentence, it is better to think of fas non esse as an impersonal expression meaning not to be right.

Because Latin commonly uses an infinitive to name the action being judged.

Here, the action is amicum fallere = to deceive a friend.

So the structure is roughly:

• fas non esse = not to be right
• amicum fallere = to deceive a friend

Together: for deceiving a friend not to be right, or more naturally in English, that it is not right to deceive a friend.

English also uses an infinitive in many similar cases, as in to deceive a friend is wrong.

Because fallere is a transitive verb and takes a direct object in the accusative.

So:

• fallere = to deceive
• amicum = a friend / the friend as the person being deceived

That makes amicum fallere mean to deceive a friend.

It is an indirect statement construction.

After verbs like:

• dicit = says
• putat = thinks
• scit = knows
• audit = hears

Latin often reports the content of the statement with an infinitive clause instead of a full finite clause.

So here:

• Pater dicit = Father says
• fas non esse amicum fallere = that it is not right to deceive a friend

One slightly tricky thing here is that the reported statement is impersonal, so you do not see the kind of personal accusative subject that often appears in indirect statement.

Because the inner statement is impersonal.

If the direct statement were something like Marcus venit, then in indirect statement you would get an accusative subject: dicit Marcum venire.

But here the direct statement is:

Fas non est amicum fallere.

That statement does not have a personal subject like Marcus. It is an impersonal idea: it is not right to deceive a friend.

So when it becomes indirect, Latin simply changes est to esse:

fas non esse amicum fallere

There is no separate personal accusative subject to add.

Non negates esse in the phrase fas non esse.

So the meaning is:

to be not right

In smoother English: it is not right to deceive a friend

This matters because the negation is aimed at the judgment of rightness, not at the action in some different way. Latin word order is flexible, but here non esse naturally gives the sense not to be right.

Yes, but it is general rather than explicitly stated.

English often does the same thing:

• To deceive a friend is wrong
• It is wrong to deceive a friend

In both languages, no specific person has to be named. The sense is general: for anyone to deceive a friend.

If Latin wanted to specify who was doing the deceiving, it could do so in a different way, but here the statement is broad and general.

Because Latin infinitives do not need a separate word like English to.

The form fallere by itself already means to deceive.

So:

• fallo = I deceive
• fallere = to deceive

English marks the infinitive with a separate word, but Latin usually does it with the verb ending itself.

Latin word order is much freer than English word order.

This sentence puts:

• the main clause first: Pater dicit
• then the reported content: fas non esse amicum fallere

Within the reported content, amicum fallere stays together as a natural verb-object unit, and fas non esse gives the judgment about that action.

So the order is natural Latin, even though English would normally reorganize it more heavily.

A more English-shaped order would be something like: Father says that deceiving a friend is not right, but Latin does not need to arrange the words that way.

Either is possible, depending on context.

Latin has no articles like English a and the, so amicum can mean:

• a friend
• the friend
• sometimes simply friend in a general sense

If the sentence is given by itself, English usually translates it as a friend, because that sounds natural in a general moral statement.

It would be:

Fas non est amicum fallere.

That is the statement the father is reporting.

Then, after Pater dicit, Latin changes it into indirect statement:

• direct: fas non est
• indirect: fas non esse

So this is a very useful pair to compare:

• Fas non est amicum fallere.
• Pater dicit fas non esse amicum fallere.