Learn Hardcore Greek: Στο εστιατόριο ο κάθε πελάτης και η κάθε πελάτισσα γράφουν τη γνώμη τους σε μια μικρή σημείωση. - At the restaurant each male customer and each female customer write their opinion on a small note.

κάθε πελάτης = every customer (general statement)
ο κάθε πελάτης = each individual customer (often with a slightly more concrete or emphatic feeling: each and every customer there)

Adding the article (ο κάθε, η κάθε) often:

Makes it feel more specific to a certain group already known from context (here: the customers of this restaurant)
Gives a nuance of each one in particular, not just a generic rule about people

You could also say:

Κάθε πελάτης γράφει τη γνώμη του.
Grammatically fine, just a bit more general in tone.

Why do we say both ο κάθε πελάτης and η κάθε πελάτισσα? Isn’t πελάτης enough for “customer”?

Traditionally, ο πελάτης (masculine) could be used generically for customer (any gender).
In this sentence, the speaker chooses to be explicitly gender-inclusive:

ο κάθε πελάτης = every male customer
η κάθε πελάτισσα = every female customer

So the phrase means every (male) customer and every (female) customer.

In everyday speech, many people would still just say:

Κάθε πελάτης γράφει τη γνώμη του.

But the original sentence avoids using only the masculine as the generic form.

Why is the verb plural (γράφουν) when ο κάθε πελάτης and η κάθε πελάτισσα each look singular?

The subject is actually a compound subject:

ο κάθε πελάτης και η κάθε πελάτισσα
→ [customer] and [female customer]

In Greek (as in English), when you join two singular subjects with και (and), the verb normally goes to plural:

Ο Γιάννης και η Μαρία γράφουν. = Giannis and Maria write.

So:

ο κάθε πελάτης και η κάθε πελάτισσα γράφουν
= every (male) customer and every (female) customer write …

Using a singular verb γράφει here would be felt as incorrect in standard Greek, because the grammar “sees” two subjects joined by και.

Why is it τη γνώμη τους and not τη γνώμη του or τη γνώμη της?

Τη γνώμη τους means their opinion, referring to all customers together.

The subject: ο κάθε πελάτης και η κάθε πελάτισσα → multiple people
So we use τους = their (3rd person plural)

If we were talking about one customer only, we would say:

Κάθε πελάτης γράφει τη γνώμη του.
(Every male customer writes his opinion.)
Κάθε πελάτισσα γράφει τη γνώμη της.
(Every female customer writes her opinion.)

Here, because the sentence refers to all customers collectively, τους (their) is the natural choice.

Why is the article written as τη γνώμη instead of την γνώμη?

The full form of the feminine accusative singular article is την:

την γνώμη (the opinion)

In everyday modern Greek, the final -ν is often dropped when the next word begins with most consonants:

την → τη before γ in γνώμη

So both:

την γνώμη
τη γνώμη

are possible; in normal writing you usually see τη γνώμη. The pronunciation hardly changes in fast speech.

What case is τη γνώμη in, and why?

Τη γνώμη is in the accusative case.

Γνώμη (opinion) is the direct object of the verb γράφουν (they write).
In Greek, the direct object goes in the accusative:
- Γράφουν τι; → τη γνώμη (τους)
  (They write what? → their opinion.)

So:

η γνώμη = the opinion (nominative, subject form)
τη γνώμη = the opinion (accusative, object form)

Why is it μια μικρή σημείωση and not έναν μικρό σημείωμα or something else? How does the indefinite article work here?

Σημείωση (note) is a feminine noun, so everything that agrees with it must be feminine singular accusative:

Indefinite article, fem. acc. sg.: μια (μία)
Adjective, fem. acc. sg.: μικρή
Noun, fem. acc. sg.: σημείωση

So:

μια μικρή σημείωση = a small note

Masculine forms like έναν μικρό … are used with masculine nouns (e.g. έναν μικρό καφέ – a small coffee), not with σημείωση, which is feminine.

What is the difference between μια and μία? Why is it μια μικρή σημείωση here?

Μια and μία are two written forms of the same word: the feminine indefinite article (a / one).

μία (with accent) is often used when you clearly mean one (single), as a number.
μια (without accent) is the unstressed article a.

In μια μικρή σημείωση, we mean a small note (not "one note" in contrast to two or three), so the unstressed article μια is normal.

You might also see μία μικρή σημείωση; in most modern texts the distinction is not strictly followed, and both are understood.

What exactly does σημείωση mean here? Could we also say σημείωμα?

Σημείωση literally means note (a short written remark). In this context it is exactly what you expect: a little piece of writing where the customer writes their opinion.

You sometimes also see:

σημείωμα = note (often a short written message / memo)
σε ένα μικρό σημείωμα would also be understandable and natural.

Nuance:

σημείωση can feel slightly more formal (also used for footnote, remark).
σημείωμα can feel like a physical note, memo, written slip.

Both could work here; the original simply chooses σημείωση.

Why is it μικρή σημείωση and not μικρό σημείωση?

Adjectives in Greek must agree in gender, number, and case with the noun they describe.

σημείωση is feminine, singular, accusative.
So the adjective must also be feminine, singular, accusative: μικρή.

If you said μικρό σημείωση, you’d be using neuter with a feminine noun, which is grammatically wrong. Compare:

ένα μικρό βιβλίο (neuter: book)
μια μικρή σημείωση (feminine: note)

Why is the word order Στο εστιατόριο ο κάθε πελάτης… instead of starting with Ο κάθε πελάτης…?

Greek word order is fairly flexible. Starting with Στο εστιατόριο:

Puts emphasis or focus on the place: As for what happens at the restaurant…
Works like a topic-setting phrase: At the restaurant, every customer writes…

You could also say:

Ο κάθε πελάτης και η κάθε πελάτισσα γράφουν τη γνώμη τους σε μια μικρή σημείωση στο εστιατόριο.

This is also correct, but the original version stylistically foregrounds the location.

Is there any special reason the sentence repeats both the article and κάθε: ο κάθε πελάτης και η κάθε πελάτισσα, instead of something shorter?

The repetition:

ο κάθε πελάτης και η κάθε πελάτισσα

instead of a compressed form like:

ο κάθε πελάτης και πελάτισσα

serves two purposes:

Grammatical clarity
Each noun has its own article in the correct gender:
- ο
  - πελάτης (masc.)
- η
  - πελάτισσα (fem.)
Stylistic / rhetorical effect
Repeating κάθε gives a rhythmic emphasis:
each and every male customer and each and every female customer.

Leaving out the second κάθε or article would sound awkward or ungrammatical in standard Greek.