Puer matri gratias agit, quod eum benigne consolatur.

Puer is in the nominative singular, which is the case normally used for the subject of the sentence. So puer is the one doing the action of agit.

It can mean either the boy or a boy, because Latin has no articles. Context tells you which English wording is most natural.

Matri is the dative singular of mater. With the idiom gratias agere alicui, the person receiving the thanks goes in the dative.

So:

• mater = mother as a subject
• matrem = mother as a direct object
• matri = to the mother / to his mother

Gratias agit is a very common Latin idiom meaning he gives thanks or simply he thanks.

The word gratias is accusative plural. In this expression, Latin normally uses the plural, even though English often just says thanks without thinking about number. So it is best learned as a set phrase:

gratias agere = to give thanks / thank

Latin often leaves out possessive words like his, her, or their when the meaning is obvious from the context.

So matri can naturally be understood as to his mother here, even though Latin does not say suae matri. Adding a possessive is possible, but Latin often prefers not to use one unless it is needed for clarity or emphasis.

Here quod is a conjunction meaning because.

It is not the relative pronoun which in this sentence. The clause quod eum benigne consolatur gives the reason why the boy thanks his mother: because she kindly comforts him.

Latin very often omits subject pronouns like he, she, and they when they are not needed. The verb ending already tells you the person and number.

Consolatur means he/she comforts. The gender is not shown by the verb itself, so you get that from context. Here the understood subject is the mother, so English supplies she.

Eum is accusative singular masculine. It is the direct object of consolatur.

In context, it refers back to puer. So the boy is:

• the subject of agit
• the object of consolatur

In other words, the boy thanks his mother because she comforts him.

This is about Latin reflexive pronouns.

Se refers back to the subject of its own clause. In the clause quod eum benigne consolatur, the understood subject is the mother. So:

• se consolatur would mean she comforts herself
• eum consolatur means she comforts him

Because the object is not the same person as the subject of that clause, Latin uses eum, not se.

Consolatur comes from consolor, consolari, which is a deponent verb.

Deponent verbs have:

• passive-looking forms
• but active meanings

So consolatur looks like a passive form, but it means he/she comforts, not he/she is comforted.

Benigne is an adverb meaning kindly, graciously, or gently.

It modifies consolatur and tells you how the mother comforts him. It comes from the adjective benignus.

Latin word order is more flexible than English word order because Latin uses case endings to show what each word is doing.

So English needs something like:

The boy thanks his mother because she kindly comforts him.

But Latin can arrange the words more freely:

Puer matri gratias agit, quod eum benigne consolatur.

This order is natural because:

• puer states the subject first
• matri gratias agit keeps the thanking expression together
• the quod clause comes after it to give the reason

A different word order would often still be grammatical, but it might sound more marked or emphatic.