Learn Hardcore Greek: Στο παλιό σχολείο οι τοίχοι καθαρίζονταν κάθε καλοκαίρι, αλλά το πάτωμα δεν σφουγγαριζόταν συχνά. - At the old school the walls were cleaned every summer, but the floor was not mopped often.

So Στο παλιό σχολείο literally is Σε + το παλιό σχολείο, "at/in the old school". Writing σε το παλιό σχολείο would be grammatically correct but sounds artificial; the contracted form is what’s normally used in speech and writing.

Why is it παλιό σχολείο and not παλιά σχολείο?

Because σχολείο is neuter, not feminine.

σχολείο: neuter noun, singular → takes το and adjectives in neuter singular.
The adjective παλιός (old) has:
- masculine: παλιός
- feminine: παλιά
- neuter: παλιό

So the correct agreement is:

το παλιό σχολείο (neuter singular)
not η παλιά σχολείο (that would mix feminine article/adjective with a neuter noun).

What grammatical role do οι τοίχοι and το πάτωμα have here? Why are they in the nominative with articles?

Both οι τοίχοι and το πάτωμα are subjects of passive verbs.

In the sentence:

οι τοίχοι καθαρίζονταν → "the walls were (being) cleaned"
το πάτωμα δεν σφουγγαριζόταν → "the floor wasn’t (being) mopped"

In Greek:

The subject of a verb (active or passive) goes in nominative:
- οι τοίχοι (nominative plural) with article οι
- το πάτωμα (nominative singular) with article το

English often omits "the" with general things ("walls", "floors"), but Greek normally keeps the definite article when you’re talking about specific things in a known place (the walls/floor of that school). So the articles are expected and natural here.

What tense and voice are καθαρίζονταν and σφουγγαριζόταν? How do they translate?

Both forms are:

Imperfect tense
Passive voice
Indicative mood

More precisely:

καθαρίζονταν = 3rd person plural imperfect passive of καθαρίζω
→ "they were being cleaned / they used to be cleaned"
σφουγγαριζόταν = 3rd person singular imperfect passive of σφουγγαρίζω
→ "it was being mopped / it used to be mopped"

So:

οι τοίχοι καθαρίζονταν → "the walls were (regularly) cleaned"
το πάτωμα δεν σφουγγαριζόταν → "the floor was not (regularly) mopped"

Why is καθαρίζονταν plural while σφουγγαριζόταν is singular?

The verb agrees in number with its subject:

οι τοίχοι = "the walls" → plural
→ (οι τοίχοι) καθαρίζονταν (3rd person plural)
το πάτωμα = "the floor" → singular
→ (το πάτωμα) δεν σφουγγαριζόταν (3rd person singular)

So the difference is purely subject–verb agreement:

plural subject → καθαρίζονταν
singular subject → σφουγγαριζόταν

Why is the imperfect used here instead of a simple past (aorist) like καθαρίστηκαν or σφουγγαρίστηκε?

The imperfect in Greek describes habitual, repeated, or ongoing actions in the past.

In this sentence:

καθαρίζονταν κάθε καλοκαίρι → emphasizes regular repetition ("were cleaned every summer", "used to be cleaned every summer")
δεν σφουγγαριζόταν συχνά → emphasizes a general habit/frequency ("wasn’t mopped often")

If you used the aorist passive:

οι τοίχοι καθαρίστηκαν → "the walls were cleaned (once / as a completed event)"
το πάτωμα δεν σφουγγαρίστηκε → "the floor was not mopped (on that occasion)"

That would sound like you’re talking about one particular time, not a habitual practice. So the imperfect fits the "every summer / often" idea.

What does κάθε καλοκαίρι mean, and why is it placed after καθαρίζονταν?

κάθε καλοκαίρι means "every summer".

κάθε = every, each
καλοκαίρι = summer

Word order in Greek is flexible. Here, κάθε καλοκαίρι comes after καθαρίζονταν:

…οι τοίχοι καθαρίζονταν κάθε καλοκαίρι…

This order is very natural: verb + time-expression. But you could also say:

Στο παλιό σχολείο, κάθε καλοκαίρι οι τοίχοι καθαρίζονταν…
Κάθε καλοκαίρι, στο παλιό σχολείο, οι τοίχοι καθαρίζονταν…

All are correct; the differences are stylistic/rhythmic, not grammatical.

Can the word order be changed? For example, could we start with Οι τοίχοι instead of Στο παλιό σχολείο?

Yes. Greek allows relatively free word order, especially for emphasis. Some possible variants:

Οι τοίχοι στο παλιό σχολείο καθαρίζονταν κάθε καλοκαίρι, αλλά το πάτωμα δεν σφουγγαριζόταν συχνά.
Στο παλιό σχολείο, οι τοίχοι καθαρίζονταν κάθε καλοκαίρι, αλλά το πάτωμα δεν σφουγγαριζόταν συχνά.
Οι τοίχοι καθαρίζονταν κάθε καλοκαίρι στο παλιό σχολείο, αλλά το πάτωμα δεν σφουγγαριζόταν συχνά.

The basic relationships (who does what, when, where) remain clear because:

οι τοίχοι / το πάτωμα are marked as subjects by their articles and nominative form.
στο παλιό σχολείο clearly expresses place.
The verbs show tense and number.

Changing order mainly shifts focus (e.g. starting with the walls emphasizes them more).

Why is it δεν σφουγγαριζόταν συχνά? Could we say δεν συχνά σφουγγαριζόταν or συχνά δεν σφουγγαριζόταν?

δεν σφουγγαριζόταν συχνά is the most neutral, natural word order:

δεν (negation) comes right before the verb.
συχνά (often) comes after the verb, modifying it.

You can change the position of συχνά for emphasis:

Δεν σφουγγαριζόταν συχνά. → neutral: "it was not mopped often."
Συχνά δεν σφουγγαριζόταν. → emphasizes how often it wasn't mopped: "it was often the case that it wasn't mopped."
Δεν συχνά σφουγγαριζόταν. → possible but sounds a bit unusual/marked; "it wasn’t often that it got mopped."

For learners, keeping δεν + verb + συχνά is the safest pattern.

What is the difference between καθαρίζονταν and σφουγγαριζόταν in meaning? Aren’t they both "were cleaned"?

Both involve cleaning, but they have different nuances:

καθαρίζω = "to clean" in a general sense.
καθαρίζονταν → "were cleaned" (could involve dusting, washing, etc.).
σφουγγαρίζω = "to mop / to clean with a mop or sponge", especially a floor.
σφουγγαριζόταν → "was mopped" (specifically the action of mopping the floor).

So the sentence is saying:

The walls got a general cleaning every summer,
but the floor was not mopped very often (a specific type of cleaning).

How would the sentence look in the active voice instead of passive?

To make it active, we must introduce an agent (who did the cleaning). For example:

Στο παλιό σχολείο οι καθαρίστριες καθάριζαν τους τοίχους κάθε καλοκαίρι, αλλά δεν σφουγγάριζαν συχνά το πάτωμα.

Breakdown:

οι καθαρίστριες = "the cleaners" (fem. pl.) as subject.
καθάριζαν τους τοίχους = "they cleaned the walls"
δεν σφουγγάριζαν συχνά το πάτωμα = "they didn’t mop the floor often"

Notice the changes:

In passive: οι τοίχοι καθαρίζονταν (walls = subject, nominative).
In active: οι καθαρίστριες καθάριζαν τους τοίχους (cleaners = subject, walls = direct object in accusative: τους τοίχους).

Is the comma before αλλά necessary, and does αλλά work like "but" in English?

Yes, αλλά works very much like "but" in English, introducing a contrast.

…, αλλά … = "…, but …"

The comma before αλλά is:

Standard and natural in this sentence, because αλλά introduces a new clause that contrasts with what comes before.
Common in Greek whenever αλλά clearly separates two clauses or ideas.

So:

…, αλλά το πάτωμα δεν σφουγγαριζόταν συχνά.
→ "…, but the floor was not mopped often."

The punctuation and usage parallel English quite closely here.