Learn Hardcore Latin: Postquam pedes lavit, puer etiam aures lavat, et nunc aures purae sunt. - After he has washed his feet, the boy also washes his ears, and now his ears are clean.

Postquam means “after” and introduces a time clause: “after (someone) did X …”
It’s followed by a verb in a normal finite tense (often the perfect), not by an infinitive.
So Postquam pedes lavit = “After he washed his feet …”.
The clause it introduces behaves like a full sentence with its own subject and verb.

Why is the verb lavit in postquam pedes lavit different from lavat later in the sentence?

Lavit is perfect tense (“he washed”), describing a completed action in the past: the feet are already washed.
Lavat is present tense (“he washes / is washing”), describing what the boy is doing now (in the narrative moment).
So the sentence contrasts a finished action (washing feet) with an action taking place now (washing ears).

Could lavit mean “he washes” (present tense) instead of “he washed”?

In form, lavit could be either present or perfect of lavare in the 3rd person singular:

present: lavat = he washes
perfect: lavit = he washed

But because it comes after postquam (“after”), the context strongly favours the perfect meaning, “he washed”.
Latin often relies on context to distinguish identical-looking present and perfect forms.

What case and number is pedes, and why is that form used?

Pedes is accusative plural (also nominative plural) of pēs, pedis (m.) = “foot”.
In postquam pedes lavit, it’s the direct object of lavit: “he washed (what?) the feet.”
Plural is used because he has two feet, and accusative because they are what is being washed.

How do we know that pedes is the object and not the subject in postquam pedes lavit?

The verb lavit is 3rd person singular (“he/she/it washed”), but pedes is plural, so they can’t agree in number.
If pedes were the subject, the verb would normally be plural (lavērunt = “they washed”).
So pedes must be the object, and the subject is an understood “he/that boy”, picked up explicitly as puer in the next clause.

Why does puer come after the clause postquam pedes lavit instead of at the start of the sentence?

Latin word order is flexible and often used for emphasis rather than for basic grammar.
Putting the time clause first (postquam pedes lavit) emphasizes the sequence: first this, then what the boy does.
Puer etiam aures lavat then introduces the subject explicitly where the new action starts.
Grammatically, it would also be correct to say Puer, postquam pedes lavit, etiam aures lavat … with a different emphasis.

What is the difference between et and etiam, and what exactly does etiam do here?

Et means simply “and.”
Etiam means “also, too, even.” It adds the idea of additional or further action.
In puer etiam aures lavat, it means: “the boy also washes his ears (in addition to his feet).”
So etiam highlights that the ears are an extra item being washed.

What case and number is aures, and how do we know?

Aures is plural of auris, auris (f.) = “ear.”
Its form can be nominative plural or accusative plural; they look the same.

In puer etiam aures lavat, aures is accusative plural, object of lavat.
In nunc aures purae sunt, aures is nominative plural, subject of sunt.
We decide which case it is in each place from its function in the clause, not the form alone.

Why is purae in the form purae and not pura or purum in nunc aures purae sunt?

Purae is feminine nominative plural, agreeing with aures (which is feminine plural).
In nunc aures purae sunt, purae is a predicate adjective after sunt: “the ears are clean.”
Adjectives in Latin must agree with the noun they describe in gender, number, and case, hence plural feminine nominative purae with aures.

Why is nunc (“now”) used if there was already an earlier action in the past?

Nunc marks what is true at the current point of the story, after the earlier action has happened.
The feet were washed before; now, in the present of the narrative, the ears are clean.
So nunc aures purae sunt = “and now the ears are clean,” stressing the present result.

Why is aures repeated in nunc aures purae sunt instead of using a pronoun like “they”?

Latin often repeats the noun where English would use a pronoun.
A pronoun can be used, but it’s more common when there is contrast or emphasis.
They could say nunc purae sunt, but that risks ambiguity if several things have been mentioned.
Repeating aures keeps the reference clear and explicit.

Can we change the word order to puer lavat etiam aures, and does that change the meaning?

You can say puer etiam aures lavat or puer aures etiam lavat; Latin word order is quite flexible.
However, etiam usually stands right before the word it modifies.
In puer etiam aures lavat, etiam clearly modifies aures (“also the ears”).
If you wrote puer lavat etiam aures, it’s understandable, but the placement of etiam is less standard and a bit clumsier in classical style.

How would this sentence change if the subject were a girl instead of a boy?

The subject puer (“boy”) would become puella (“girl”), which is also nominative singular.
The rest of the sentence can stay the same, because the verbs are 3rd person singular and don’t change for gender, and purae agrees with aures, not with the subject.
So you’d get: Postquam pedes lavit, puella etiam aures lavat, et nunc aures purae sunt.