Mater dicit mendacium turpe esse.

Because Latin often uses an accusative + infinitive construction after verbs of saying, thinking, knowing, and perceiving.

So instead of saying:

• Mother says that a lie is shameful

Latin literally says something more like:

• Mother says a lie to be shameful

That is why you get:

• dicit = says
• mendacium turpe esse = a lie to be shameful

This is one of the most important sentence patterns in Latin.

Because after dicit, Latin normally puts the reported statement into an infinitive clause.

So:

• est = is
• esse = to be

In English we would usually say:

• Mother says that a lie is shameful

But Latin prefers:

• Mother says a lie to be shameful

So esse is exactly what we expect in this construction.

In this sentence, mendacium is the subject of the infinitive esse.

In an accusative-and-infinitive construction, the subject of the infinitive normally goes into the accusative case.

So here mendacium is accusative.

However, there is something that can confuse learners: mendacium is a neuter singular noun of the second declension, and its nominative and accusative forms are identical. So the form looks the same either way.

That means:

• nominative singular: mendacium
• accusative singular: mendacium

So even though it looks like a nominative, here it functions as an accusative.

Because turpe agrees with mendacium.

Since mendacium is neuter singular, the adjective describing it must also be neuter singular:

• mendacium = lie, neuter singular
• turpe = shameful, neuter singular

Also, since mendacium is functioning as the subject of the infinitive inside an accusative-and-infinitive construction, the predicate adjective also matches that structure.

So mendacium turpe esse means:

• a lie to be shameful

Yes. It is the whole indirect statement after dicit.

You can divide the sentence like this:

• Mater = the main subject
• dicit = the main verb
• mendacium turpe esse = what the mother says

So the structure is:

• Mater / dicit / mendacium turpe esse
• Mother / says / that a lie is shameful

That final part is not just random extra words; it is the content of the statement.

Here are the main forms:

• mater — mater, matris — mother
• dicit — from dico, dicere, dixi, dictum — say
• mendacium — mendacium, mendacii — lie, falsehood
• turpe — from turpis, turpe — shameful, disgraceful
• esse — from sum, esse, fui — to be

A learner may especially want to notice that:

• dicit is 3rd person singular present active
• esse is the infinitive of sum

Yes. Latin word order is much freer than English word order because the grammar is shown mostly by endings, not by position.

So these could still mean essentially the same thing:

• Mater dicit mendacium turpe esse
• Mater mendacium turpe esse dicit
• Mendacium turpe esse mater dicit

The version you were given is perfectly natural. Putting esse at the end is especially common in Latin.

Most directly, mendacium means a lie, falsehood, or untruth.

Depending on the English translation shown to the learner, it might sometimes be rendered a little more naturally as lying in a general sense. But grammatically the Latin word itself is a noun meaning lie.

So the sentence can be understood as something like:

• Mother says that a lie is shameful
• or more idiomatically, Mother says that lying is shameful

The exact English wording can vary, even though the Latin structure stays the same.

Because mater is the subject of the main verb dicit, not the subject of esse.

There are really two layers in the sentence:

1. Main clause:

   • Mater dicit = Mother says

2. Indirect statement:

   • mendacium turpe esse = that a lie is shameful

So:

• mater is nominative because it is the subject of dicit
• mendacium is accusative because it is the subject of the infinitive esse

The direct statement would be:

• Mendacium turpe est.
• A lie is shameful.

Then to turn it into reported speech after dicit, Latin changes the finite verb est into the infinitive esse, and the subject of that clause goes into the accusative:

• Mendacium turpe est.
• Mater dicit mendacium turpe esse.

Because mendacium is neuter singular, its form does not visibly change between nominative and accusative, but the construction has still changed grammatically.

In this sentence it clearly means shameful, disgraceful, or morally base.

The adjective turpis, turpe often refers to something dishonorable, disgraceful, or ugly in a moral sense, not just physically unattractive.

So mendacium turpe esse means more than merely a lie is unpleasant. It means that a lie is morally disgraceful.

A very literal breakdown would be:

• Mater = Mother
• dicit = says
• mendacium = a lie
• turpe = shameful
• esse = to be

So the literal order is:

• Mother says a lie shameful to be

That is awkward English, but it helps show the Latin grammar.

A more natural English translation is:

• Mother says that a lie is shameful.