Puer flens matrem vocat.

Because they are in different cases.

• puer is nominative singular, the case usually used for the subject of the sentence.
• matrem is accusative singular, the case usually used for the direct object.

So in Puer flens matrem vocat:

• puer = the one doing the action
• matrem = the person being called

The different endings show their jobs in the sentence.

Because vocat means calls, and the person being called is the direct object of that verb.

In Latin, the direct object is normally put in the accusative case. So:

• mater = mother, as a dictionary form
• matrem = mother, as a direct object

That is why Latin uses matrem, not mater, here.

flens is the present active participle of flere, meaning crying or weeping.

A participle is a verbal adjective: it comes from a verb, but it describes a noun.

So flens describes puer:

• puer flens = the crying boy / the boy who is crying

It combines the idea of a verb (crying) with the function of an adjective (describing boy).

Because flens agrees with puer, which is nominative singular.

Participles, like adjectives, must agree with the noun they describe in:

• gender
• number
• case

Since puer is:

• masculine
• singular
• nominative

the participle must also be nominative singular, so we get flens.

If the participle were describing matrem, it would need to be accusative singular, and then the form would be different.

Yes. The present participle usually shows an action happening at the same time as the main verb.

So Puer flens matrem vocat means the boy is:

• crying
• and calling his mother

These actions are understood as simultaneous.

vocat is present tense, active voice, indicative mood, third person singular.

That means:

• present = happening now
• active = the subject does the action
• indicative = a straightforward statement
• third person singular = he/she/it calls

So vocat means he calls or she calls. Here, because the subject is puer, it means the boy calls.

Because classical Latin does not have articles like English the and a/an.

So puer can mean:

• a boy
• the boy

and matrem can mean:

• a mother
• the mother
• sometimes more naturally, his mother, depending on context

The exact English wording depends on the context and the meaning already understood.

Latin word order is much freer than English word order because the endings show the grammatical roles.

Putting the verb at the end is very common in Latin, especially in simple prose. So:

• Puer flens matrem vocat

is a very natural Latin order:

• subject
• descriptive participle
• object
• verb

But Latin could rearrange the words for emphasis without changing the basic meaning, because the endings still show who is doing what.

Yes. Both are reasonable.

puer flens literally means boy crying, but in natural English you might translate it as:

• the crying boy calls his mother
• the boy, crying, calls his mother
• the boy who is crying calls his mother

Latin participles often give English several possible translations, depending on what sounds most natural in context.

We know because of agreement.

• puer is nominative singular
• flens is also nominative singular

So flens matches puer.

But matrem is accusative singular, so if the participle described matrem, it would need an accusative form instead.

The matching case helps show which noun the participle belongs to.

The dictionary forms are:

• matrem → mater
• flens → from the verb flere

More precisely:

• mater, matris = mother
• flere = to cry, to weep

And flens is the participial form made from flere.

It is both in a sense, which is exactly what a participle is.

• It comes from a verb: flere
• But in the sentence it behaves like an adjective, because it describes puer

So it has verbal meaning (crying) but adjectival grammar (it agrees with the noun it modifies).

That is why participles are often explained as verbal adjectives.