Haec verba a puero non intelleguntur, sed a puella intelleguntur.

The sentence has two parallel clauses:

• Haec verba a puero non intelleguntur
• sed a puella intelleguntur

In both clauses:

• haec verba is the subject
• intelleguntur is the verb
• a puero / a puella tells you who is doing the action in a passive construction

So Latin is saying that these words are not understood by the boy, but are understood by the girl.

Because verba is plural, while verbum is singular.

• verbum = word
• verba = words

Verbum is a second-declension neuter noun, and neuter plural nominative/accusative forms end in -a, so verba is exactly the form you would expect for words.

Because haec is agreeing with verba, which is neuter plural.

The demonstrative hic, haec, hoc can have several forms that look the same in English. Here:

• haec verba = these words

This particular haec is neuter plural nominative/accusative.

A common source of confusion is that haec can also be feminine singular in other contexts. The noun it goes with tells you which one it is.

Here it is nominative, because the sentence is passive and haec verba is the subject of intelleguntur.

A useful comparison:

• Active: Puer haec verba non intellegit.
• Passive: Haec verba a puero non intelleguntur.

In the active sentence, haec verba would be the direct object, so accusative. In the passive sentence, it becomes the subject, so nominative.

Because neuter plural nominative and accusative look the same, the form itself does not change here; the job in the sentence changes.

The ending -ntur shows that the verb is:

• third person plural
• present tense
• passive
• indicative

So intelleguntur means they are understood.

That matches haec verba, which is plural. Since the subject is plural, the verb must also be plural.

Because Latin changes noun endings depending on their grammatical role.

The dictionary forms are:

• puer = boy
• puella = girl

But after a/ab in a passive sentence, a personal agent is put in the ablative:

• a puero = by the boy
• a puella = by the girl

So:

• puer becomes puero
• puella becomes puella

The feminine first-declension ablative singular happens to look the same as the nominative singular in puella, but the function is different.

In a passive sentence, Latin normally uses a or ab plus the ablative to show the personal agent: the person by whom the action is done.

So:

• a puero = by the boy
• a puella = by the girl

This is called the ablative of agent.

It is especially used with people or other animate agents in passive constructions.

Here it means by, not from.

The preposition a/ab can indeed mean from in many contexts, but in a passive construction with a person, it marks the agent:

• a puero intelleguntur = they are understood by the boy

So the grammar of the sentence tells you how to understand it.

Before a consonant, Latin often uses a; before a vowel or h, ab is especially common.

So:

• a puero is normal
• ab amico is also normal

You may sometimes see variation, but a puero is the expected form here.

Because non negates the verb: are not understood.

Latin word order is more flexible than English word order, but placing non right before the verb is very common and very clear.

So:

• non intelleguntur = are not understood

Sed means but and introduces a contrast.

The contrast here is between:

• a puero non intelleguntur
• sed a puella intelleguntur

So the sentence sets up an opposition between the boy and the girl.

Yes. Latin word order is fairly flexible because the endings show the grammatical relationships.

For example, Latin could rearrange parts of the sentence and still keep the same basic meaning, as long as the forms stay clear.

The given order is natural and easy to follow because it:

• starts with haec verba
• gives the first agent and verb
• then uses sed to introduce the contrasting second clause

So this word order is not the only possible one, but it is a clear and elegant one.

Sometimes Latin does omit a repeated verb when the meaning is obvious. So something like this could be understood:

• Haec verba a puero non intelleguntur, sed a puella

However, repeating intelleguntur makes the sentence balanced and explicit. For a learner, it is especially helpful because both clauses are fully stated.

So the repetition is not strange; it is clear and stylistically neat.