Mater cubitum pueri sapone et aqua tepida lavat.

Latin shows this mainly through case endings and the verb ending, not just word order.

• Mater is nominative singular, so it is the subject: the one doing the action.
• Cubitum is accusative singular, so it is the direct object: the thing being washed.
• Lavat is 3rd person singular, so it matches a singular subject like mater.

So the core structure is:

• mater = the washer
• cubitum = the thing washed
• lavat = washes

Because it is the direct object of lavat.

The verb lavat means washes, and in Latin the direct object usually goes in the accusative case. So cubitum means elbow in the accusative singular form.

Its dictionary form is cubitus (or listed similarly in a dictionary), and cubitum is the form you use for the elbow as the object of the verb.

Because pueri can indeed have more than one possible meaning by form alone:

• genitive singular = of the boy
• nominative plural = the boys

But in this sentence, genitive singular makes sense.

Why?

• The sentence already has a subject: mater
• It already has a direct object: cubitum
• So pueri is naturally understood as showing possession: the boy’s elbow

This is a very common Latin pattern:

• noun + genitive
• cubitum pueri = the boy’s elbow

Because Latin often places a genitive noun after the noun it depends on.

So:

• cubitum pueri = the elbow of the boy = the boy’s elbow

English often prefers the possessive first (the boy’s elbow), but Latin very commonly uses:

• head noun + genitive
• cubitum pueri

That is perfectly normal Latin word order.

Because Latin can express with by using the ablative case without a preposition when it means by means of / using something.

So:

• sapone = with soap
• aqua tepida = with warm water

This is called the ablative of means or instrument.

Latin often does this with tools or substances:

• gladio pugnat = he fights with a sword
• aqua lavat = he washes with water

So no separate word for with is needed here.

Because they are from different nouns, and different nouns form the ablative singular differently.

• sapo becomes sapone
• aqua becomes aqua

Both are still ablative singular, even though they do not look the same.

That is normal in Latin: the case is the same, but the ending depends on the declension of the noun.

So both of these mean instruments or means:

• sapone = with soap
• aqua tepida = with warm water

Because it agrees with aqua.

Latin adjectives must agree with the nouns they modify in:

• gender
• number
• case

Here:

• aqua is feminine
• singular
• ablative

So the adjective must also be:

• feminine
• singular
• ablative

That gives tepida.

It does not agree with sapone, because tepida modifies only aqua, not both nouns together. So the phrase means:

• with soap and warm water

not

• with warm soap and water

Because Classical Latin has no articles.

Latin does not have separate words for:

• the
• a / an

So mater can mean:

• mother
• the mother
• sometimes even a mother

and the exact English choice depends on context.

The same is true for the other nouns in the sentence.

Because Latin word order is much more flexible than English word order.

Latin often puts the verb at the end, especially in straightforward prose. So this sentence follows a very common pattern:

• subject
• object
• other details
• verb

That said, Latin can move words around for emphasis, style, or clarity, because the case endings still show each word’s job.

So Mater cubitum pueri sapone et aqua tepida lavat is natural Latin even though English would usually put washes earlier.

Lavat is:

• present tense
• active voice
• indicative mood
• 3rd person singular

So it means:

• she washes
• he washes
• it washes

Here it must mean she washes, because the subject is mater.

Also, Latin present tense can cover both:

• washes
• is washing

Context tells you which English translation sounds best.

Yes, it could have.

Because lavat already tells you the subject is 3rd person singular, Latin often leaves the subject pronoun or noun unstated when it is clear from context.

So Lavat by itself can mean:

• he/she is washing
• he/she washes

But Latin includes mater here to make the subject explicit. That can help with:

• clarity
• emphasis
• introducing the subject

So both are possible, but mater makes the sentence clearer and more complete on its own.