Learn Hardcore Greek: Την Κυριακή είναι καλή ιδέα να πάμε σινεμά με τον παππού και τη γιαγιά. - On Sunday it is a good idea to go to the cinema with grandpa and grandma.

Κυριακή is a feminine noun (Sunday).
Its form is the same in nominative and accusative: Κυριακή.
The article shows the case:
- Η Κυριακή = Sunday (as subject, nominative)
- Την Κυριακή = on Sunday (accusative, used adverbially)

So Την Κυριακή here means on Sunday, even though literally it looks like the Sunday. This is a standard Greek pattern.

Could we say Κυριακή είναι καλή ιδέα... without Την? What difference would that make?

You could say Κυριακή είναι καλή ιδέα..., but it sounds more like a heading or a more telegraphic style (for example, in a note or timetable).

In normal, natural speech, Την Κυριακή with the article is preferred when you mean on Sunday (this coming Sunday / a specific Sunday we have in mind).

Την Κυριακή πάμε σινεμά. = On Sunday we are going to the cinema. (normal, natural)
Κυριακή πάμε σινεμά. = Possible, but sounds a bit clipped or stylistic.

So the article Την is the usual, idiomatic choice.

Why is the verb είναι placed after Την Κυριακή? Could we change the word order?

Greek word order is fairly flexible, especially with elements like time expressions. You can say:

Την Κυριακή είναι καλή ιδέα να πάμε σινεμά...
Είναι καλή ιδέα την Κυριακή να πάμε σινεμά...
Είναι καλή ιδέα να πάμε σινεμά την Κυριακή...

All are grammatically correct. The choice changes the emphasis slightly:

Starting with Την Κυριακή highlights the time: As for Sunday, it’s a good idea...
Putting Την Κυριακή later focuses first on the fact that it is a good idea, then adds when.

But none of these changes the basic meaning.

What is the function of να in να πάμε σινεμά?

Να introduces a subjunctive clause. In this sentence it corresponds roughly to English to in to go, or that we go.

είναι καλή ιδέα να πάμε σινεμά = literally it is a good idea that we go to the cinema / it is a good idea to go to the cinema.

After many expressions like είναι καλή ιδέα, θέλω, πρέπει, Greek uses να + verb instead of an infinitive (since Modern Greek no longer has a separate infinitive form).

So να πάμε is the normal way to say to go (we) in this context.

Why is it πάμε and not something like πηγαίνουμε here?

Both πάμε and πηγαίνουμε are first-person plural forms of πάω / πηγαίνω (to go), but:

πάμε is shorter, more colloquial, and very common in speech.
πηγαίνουμε is a bit more neutral/formal and often used as a plain present (we go / we are going).

After να, Greek often uses πάμε as the default choice in everyday speech:

να πάμε σινεμά sounds natural and conversational.
να πηγαίνουμε σινεμά would usually imply a repeated or habitual action (that we keep going to the cinema), which is not what is meant here.

So να πάμε fits the idea of going (once) to the cinema.

Why is there no subject pronoun (like εμείς) before πάμε?

Greek is a pro-drop language: subject pronouns are usually omitted because the verb ending already shows the person and number.

πάμε clearly indicates we go.
Saying εμείς πάμε is only needed for emphasis (for example, contrasting with others: εμείς πάμε, αυτοί μένουν = we are going, they are staying).

In this sentence, there is no contrast, so εμείς is not needed. να πάμε alone is perfectly normal.

Why does Greek say πάμε σινεμά without a preposition, while English says go to the cinema?

Greek often omits a preposition with certain verbs + places when the destination is very clear from usage. πάω σινεμά is a fixed, idiomatic pattern meaning go to the cinema.

πάω σινεμά = I go to the cinema.
You could also say πάω στο σινεμά, which is also correct, but πάω σινεμά is very common and a bit more colloquial.

So να πάμε σινεμά is the natural way to express to go to the cinema, even though there is no σε in Greek.

What kind of word is σινεμά? Does it change form?

Σινεμά is a neuter noun borrowed from French cinéma. In Modern Greek it is indeclinable, meaning its form does not change for case or number:

το σινεμά (nominative / accusative singular)
τα σινεμά (nominative / accusative plural) – same stem

In this sentence, σινεμά is in the accusative as the object of πάμε, but you see no change in its form; the case is understood from its position and function.

Why is it με τον παππού και τη γιαγιά and not με ο παππούς και η γιαγιά?

After the preposition με (with), Greek uses the accusative case, not nominative.

Nominative (used for the subject):
- ο παππούς, η γιαγιά
Accusative (used after με):
- τον παππού, τη(ν) γιαγιά

So:

με τον παππού = with grandpa
με τη γιαγιά = with grandma

English does not mark case on nouns like this, but in Greek the article (and sometimes the noun) changes form.

Why is it τη γιαγιά and not την γιαγιά?

The feminine accusative article has two forms in writing: την and τη. The final -ν can be dropped before certain consonants in modern usage to avoid awkward clusters.

A common rule of thumb: keep the -ν before vowels and the consonants κ, π, τ, ξ, ψ, γκ, μπ, ντ, τσ, τζ; it is often dropped before others.

Before γ (as in γιαγιά), many writers drop it: τη γιαγιά.
You will also see την γιαγιά; it is not wrong, just a different stylistic choice.

So τη γιαγιά is a standard modern spelling, especially in informal or neutral texts.

Why is the article used with παππού and γιαγιά if English usually says just grandpa and grandma?

Greek uses the definite article much more frequently than English, especially:

with family members,
when referring to specific, known people.

So με τον παππού και τη γιαγιά naturally means with grandpa and grandma, usually understood as our grandparents from context.

If you added a possessive, you would normally still keep the article:

με τον παππού μου και τη γιαγιά μου = with my grandpa and my grandma.

Dropping the article here would sound strange or very marked.

Does τον παππού και τη γιαγιά mean both grandparents together, or could it be any grandpa and grandma?

Grammatically, it is the grandpa and the grandma, singular each, so it refers to one grandfather and one grandmother. In context, this almost always means our grandpa and grandma (one set of grandparents), unless the context clearly indicates something else.

If someone wanted to talk about more than one set, they would typically clarify:

με τους παππούδες και τις γιαγιάδες = with the grandfathers and the grandmothers.

In everyday use, τον παππού και τη γιαγιά is understood as grandpa and grandma (ours).

Is σινεμά formal or informal? Is there a more formal word?

Σινεμά is colloquial and very common in everyday speech, like English movies.

A more formal or more standard term is:

κινηματογράφος (cinema)

You might see:

να πάμε στον κινηματογράφο in more formal writing.
In ordinary conversation, people almost always say πάμε σινεμά.