Magistra dicit hanc locutionem rectam esse.

Because after verbs like dicit (says), Latin often uses indirect statement.

In an indirect statement:

• the subject of the reported statement goes into the accusative
• the verb of the reported statement goes into the infinitive

So instead of a direct statement like:

• Haec locutio recta est = This expression is correct

Latin changes it after dicit to:

• hanc locutionem rectam esse

That is why locutio becomes locutionem, and recta becomes rectam.

It is an accusative-and-infinitive construction, often called an indirect statement.

Here is the breakdown:

• hanc locutionem = the subject of the indirect statement, in the accusative
• rectam = an adjective describing locutionem, also in the accusative
• esse = the infinitive to be

So literally it is something like:

• The teacher says this expression to be correct

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

Because hanc agrees with locutionem, which is accusative singular feminine.

The forms are:

• haec locutio = this expression as the subject
• hanc locutionem = this expression as the accusative

Since the phrase is inside an indirect statement, the subject of that statement must be accusative, so Latin uses hanc, not haec.

Because rectam is modifying locutionem, and adjectives must agree with the nouns they describe in:

• gender
• number
• case

Locutionem is:

• feminine
• singular
• accusative

So the adjective must also be:

• feminine
• singular
• accusative

That gives rectam.

If the sentence were a direct statement, you would get:

• Haec locutio recta est

But in indirect statement:

• hanc locutionem rectam esse

Because indirect statement in Latin uses the infinitive, not a finite verb.

So:

• direct statement: Haec locutio recta est = This expression is correct
• reported after dicit: Magistra dicit hanc locutionem rectam esse = The teacher says that this expression is correct

Latin does not normally use quod here the way English uses that. Instead, it switches to the accusative-and-infinitive pattern.

Classical Latin normally prefers the accusative + infinitive after verbs of saying, thinking, knowing, hearing, and so on.

So the standard Classical pattern is:

• Magistra dicit hanc locutionem rectam esse

A quod clause can appear in later Latin or in some special contexts, but for a learner of standard Classical Latin, the sentence you have is the normal and expected construction.

Here is the parsing:

• Magistra — nominative singular feminine
  
  • subject of dicit
• dicit — 3rd person singular present active indicative
  
  • says
• hanc — accusative singular feminine
  
  • modifies locutionem
• locutionem — accusative singular feminine
  
  • subject of the indirect statement
• rectam — accusative singular feminine
  
  • predicate adjective agreeing with locutionem
• esse — present active infinitive of sum
  
  • verb of the indirect statement

Because in Latin indirect statement, the logical subject of the reported idea is put into the accusative.

In English, we say:

• The teacher says that this expression is correct

Inside the that clause, this expression is the subject.

But Latin handles that differently:

• dicit hanc locutionem rectam esse

So even though this expression is the thing being described as correct, it appears in the accusative because of the indirect statement construction.

Because rectam is a predicate adjective linked with locutionem through esse.

In Latin, predicate adjectives agree with the noun they describe. Since locutionem is accusative singular feminine, rectam must match it.

Compare:

• Puella laeta est = The girl is happy
• Dico puellam laetam esse = I say the girl is happy

Here the adjective changes case along with the noun.

Yes.

Its dictionary form is:

• locutio, locutionis — feminine

That makes it a third-declension noun.

Relevant forms here are:

• nominative singular: locutio
• accusative singular: locutionem

That is why the sentence has locutionem.

Latin word order is flexible, but infinitives in indirect statement often come at or near the end of the clause.

So hanc locutionem rectam esse is a very natural order.

The order helps show the structure:

• hanc locutionem = the accusative subject
• rectam = predicate adjective
• esse = infinitive completing the indirect statement

Latin could rearrange the words for emphasis, but this order is straightforward and common.

The direct statement would be:

• Haec locutio recta est.

Then after dicit, Latin converts it into indirect statement:

• Magistra dicit hanc locutionem rectam esse.

So a useful way to understand the grammar is:

1. Start with the direct statement: Haec locutio recta est
2. Put it into indirect statement:
   • haec → hanc
   • locutio → locutionem
   • recta → rectam
   • est → esse

In many beginner Latin contexts, magistra usually means teacher or female teacher.

Although English historically had other words related to it, teacher is usually the natural translation in a sentence like this.

So:

• Magistra dicit ... = The teacher says ...

Usually, yes.

Locutio can mean things like:

• expression
• phrase
• wording
• turn of phrase

The best English choice depends on context. In a classroom context about language, this expression is a very natural translation.

So hanc locutionem rectam esse means that the teacher says this particular wording or expression is correct.