Puer sub lecto clavem invenit.

Because puer is in the nominative singular, which is the case normally used for the subject of a sentence.

So in Puer sub lecto clavem invenit, puer means the boy / a boy and is the one doing the action.

A native English speaker often expects the subject to be identified mostly by word order, but in Latin it is usually identified by its case ending instead.

Because clavem is the accusative singular form of clavis, meaning key.

The accusative case is commonly used for the direct object, the thing directly affected by the action of the verb. Here, the boy is finding the key, so clavem is in the accusative.

So:

• clavis = key
• clavem = key, as a direct object

Because sub can take two different cases, depending on the meaning:

• with the ablative = under in the sense of location
• with the accusative = under in the sense of motion toward

Here, sub lecto means under the bed as a place, not movement toward that place.

So:

• sub lecto = under the bed / beneath the bed
• sub lectum would suggest movement, such as to a position under the bed

Lecto is ablative singular of lectus, meaning bed.

It is ablative here because it follows sub in the sense of location.

So the structure is:

• sub = under
• lecto = bed, in the ablative
• sub lecto = under the bed

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

So puer can mean:

• the boy
• a boy

And clavem can mean:

• the key
• a key

Which one is best depends on context or on the translation you have been given.

It can be ambiguous when macrons are not written.

Without macrons, invenit could represent either:

• invenit = finds (present tense)
• invēnit = found / has found (perfect tense)

Many beginner texts leave out macrons, so you often need the context or the given translation to know which tense is meant.

This is a very common source of confusion for learners.

Yes. It is perfectly natural Latin.

Latin word order is more flexible than English word order because the endings show the grammatical roles. A sentence like this can be rearranged in different ways without changing the basic meaning.

For example, Latin often puts the verb near the end, as here:

• Puer sub lecto clavem invenit

That is a very common pattern.

English has to rely much more on word order, but Latin relies much more on cases.

Often, yes.

Because the forms show their jobs in the sentence, these could still express the same basic idea:

• Clavem puer sub lecto invenit
• Sub lecto puer clavem invenit
• Puer clavem sub lecto invenit

The difference would usually be one of emphasis or style, not of core meaning.

That said, some word orders sound more natural than others in a given context.

By itself, the phrase can be somewhat ambiguous, just as English can be.

English The boy found the key under the bed can mean:

• the key was under the bed, or
• the boy was under the bed when he found it

Latin can sometimes leave that to context too.

In a simple sentence like this, many learners will naturally understand sub lecto as giving the location of the finding, often understood as the key being under the bed. But strict context is what makes it fully clear.

They are:

• puer, puerī = boy
• sub = under
• lectus, lectī = bed
• clāvis, clāvis = key
• inveniō, invenīre, invēnī, inventum = find

Knowing dictionary forms helps you recognize why the words look different in the sentence:

• puer stays puer in the nominative singular
• lectus becomes lecto
• clavis becomes clavem
• inveniō becomes invenit / invēnit depending on tense

A very literal, word-for-word version would be something like:

Boy under bed key finds/found

That sounds wrong in English, but it helps show how Latin is built.

A normal English translation then rearranges the words into natural English order, using the case endings to understand who is doing what.