Learn Hardcore Latin: Puella caput fratris lavare non vult, sed manus suas lavat. - The girl does not want to wash her brother's head, but she washes her own hands.

lavare is the present active infinitive of lavo, lavare = to wash.
The pattern is: volo + infinitive = I want to …
- puella lavare vult = the girl wants to wash
- puella lavare non vult = the girl does not want to wash

If you said puella caput fratris non lavat, it would mean the girl does not wash her brother’s head (a simple statement of fact), not does not want to wash. The infinitive is needed to express the idea of wanting to do something.

Why does non go in front of vult rather than in front of lavare?

Non normally negates the finite verb (the conjugated verb in the clause).

Here, the finite verb is vult.
lavare is an infinitive, dependent on vult.

So lavare non vult literally means she does not want to wash (the wanting is negated).

If you put non just before lavare, Latin speakers would still usually understand that you are negating the want, but non lavare vult can more strongly suggest something like she wants not to wash, i.e. she positively wants the not-washing. The usual, neutral way to say does not want to wash is lavare non vult.

What case is caput, and how is it functioning in the sentence?

Caput is:

nominative or accusative singular, neuter, 3rd declension (caput, capitis = head).

In this sentence it must be accusative singular, because it is the direct object of the verb lavare:

caput [acc.] lavare = to wash (the) head

Latin neuter nouns have the same form in nominative and accusative, so context and syntax tell you which it is; here, it is clearly being washed, so it is the object.

What case is fratris, and what does caput fratris mean grammatically?

Fratris is:

genitive singular of frater, fratris = brother.

The genitive case often expresses possession or close relation. So:

caput fratris = the head of (the) brother, i.e. the brother’s head.

Grammatically:

caput = head (accusative object of lavare)
fratris = genitive, showing whose head it is

So puella caput fratris lavare non vult = the girl does not want to wash her brother’s head.

Why does Latin use caput fratris instead of a separate word for “of” or an ’s ending as in English?

Latin doesn’t use a separate word for English of or the possessive ’s. Instead, it uses the genitive case on the “owner” word:

frater (nom.) = brother
fratris (gen.) = of (the) brother / the brother’s

So:

caput fratris = head of (the) brother / the brother’s head
liber puellae = book of the girl / the girl’s book

The genitive ending itself does the work that of or ’s would do in English.

What is manus in manus suas lavat in terms of case, number, and gender, and how do we know it’s an object?

Manus here comes from manus, manūs (4th declension) = hand.

For manus:
- nominative plural and accusative plural have the same form: manus
- gender: feminine

In manus suas lavat:

lavat = (she) washes
The thing being washed must be in the accusative.
So manus here is accusative plural feminine = (her) hands.

We know it’s the object because puella is already the subject (nominative), and lavat needs a direct object; manus suas fills that role.

Why is it suas and not eius for “her hands”?

Latin distinguishes between reflexive and non‑reflexive possessives:

suus, sua, suum (and its plural forms) = his own, her own, its own, their own
– refers back to the subject of the clause.
eius = his / her / its (belonging to someone else, not the subject).

In this sentence, the subject is puella (the girl), and the hands belong to that same girl. So Latin uses the reflexive possessive:

manus suas lavat = she washes her own hands.

If you said manus eius lavat, it would mean she washes her hands, where the hands belong to some other female, not to the girl who is doing the washing.

Why is suas feminine plural, and what does it agree with?

Latin possessive adjectives agree with the noun they describe, not with the possessor.

manus (here) = accusative plural, feminine
So suus, -a, -um must take the form that matches manus:
- feminine
- plural
- accusative

That form is suas.

So:

manus suas = her own hands
Even though the owner is puella (singular feminine), the possessive agrees with manus (plural feminine), not with puella.

Can the word order of the sentence be changed, and would that change the meaning?

Latin word order is relatively flexible, especially compared to English. You can rearrange many parts without changing the basic meaning, though emphasis can shift.

For example, all of these are grammatically possible and mean essentially the same thing:

Puella caput fratris lavare non vult, sed manus suas lavat.
Puella lavare caput fratris non vult, sed manus suas lavat.
Caput fratris lavare puella non vult, sed manus suas lavat.

The forms (endings) show the roles:

puella = subject (nominative)
caput = object (accusative)
fratris = possessor (genitive)
manus suas = object (accusative)
vult / lavat = verbs

Changing the order mainly changes what is emphasised, not who is doing what to whom.