Learn Hardcore Greek: Η πιθανότητα να έχουμε επιτυχία φέτος είναι μεγάλη. - The chance that we will have success this year is high.

Η is the definite article, feminine, singular, nominative.
Πιθανότητα here is also feminine, singular, nominative and is the subject of the sentence.
The verb είναι (is) links the subject Η πιθανότητα with the predicate adjective μεγάλη (big / high).

So:
Η πιθανότητα … είναι μεγάλη = The probability … is high, with all three key words (η – πιθανότητα – μεγάλη) in feminine singular nominative agreeing with each other.

Could we use a plural form like Οι πιθανότητες instead of Η πιθανότητα? Would it change the meaning?

Yes, you can also say:

Οι πιθανότητες να έχουμε επιτυχία φέτος είναι μεγάλες.

Differences:

Η πιθανότητα … είναι μεγάλη = The probability is high (more abstract/single quantity).
Οι πιθανότητες … είναι μεγάλες = The chances are good/high (sounds a bit more colloquial, focusing on multiple “chances”).

Grammatically:

Οι πιθανότητες: feminine, plural, nominative.
The adjective must then also be plural: μεγάλες instead of μεγάλη.

Both versions are natural; it’s mainly a style preference.

What is the function of να in να έχουμε επιτυχία? Is έχουμε in a special mood or tense?

Να introduces the subjunctive mood in Modern Greek.

Έχουμε here is the subjunctive form of the verb έχω (to have).
In Modern Greek, the present subjunctive often has the same form as the present indicative; what tells you it’s subjunctive is the particle να in front of it.

So:

έχουμε alone = we have (indicative).
να έχουμε = that we (may) have / for us to have (subjunctive, dependent on another word like πιθανότητα, θέλω, μπορεί, etc.).

In this sentence να έχουμε επιτυχία is a subordinate clause that functions like an object/complement of πιθανότητα:
η πιθανότητα [να έχουμε επιτυχία] = the probability [that we will have success].

If έχουμε is “present”, why does να έχουμε επιτυχία φέτος refer to the future (“this year”)?

In Modern Greek, the present subjunctive is the default way to talk about future events inside να-clauses.

Time reference (present vs future) is usually given by context or by an explicit time word like φέτος (this year), αύριο (tomorrow), etc.
So να έχουμε επιτυχία φέτος naturally means that we will have success this year, even though the verb form is called “present” in grammar terms.

Compare:

Θέλω να πάω αύριο. = I want to go tomorrow.
Υπάρχει πιθανότητα να βρέξει σήμερα. = There is a chance it will rain today.

In both cases, the present subjunctive talks about the future.

Why does Greek say να έχουμε επιτυχία (“to have success”) instead of a simple verb like να πετύχουμε (“to succeed”)? Are both correct?

Both are correct but have slightly different nuances:

Να έχουμε επιτυχία
- Literally: to have success.
- Focuses on the state/result of success.
- Sounds quite natural and neutral in many contexts.
Να πετύχουμε
- Literally: to succeed / to achieve (it).
- Focuses more on the achievement / act of succeeding.
- Often feels a bit more dynamic.

You could say:

Η πιθανότητα να πετύχουμε φέτος είναι μεγάλη.
(The probability that we’ll succeed this year is high.)

That is also perfectly natural. The original να έχουμε επιτυχία just chooses a noun phrase (επιτυχία) instead of a verb of success (πετυχαίνω / πετύχω), but the overall meaning is the same.

What exactly does φέτος mean, and where can it go in the sentence? Is there any difference from εφέτος?

Φέτος means this year and functions like an adverb of time.

It does not take an article (you don’t say το φέτος here).
In this sentence it appears inside the να-clause:
να έχουμε επιτυχία φέτος.

You can move it around quite freely:

Η πιθανότητα να έχουμε επιτυχία φέτος είναι μεγάλη.
Η πιθανότητα να έχουμε φέτος επιτυχία είναι μεγάλη.
Η πιθανότητα φέτος να έχουμε επιτυχία είναι μεγάλη.

All are grammatical. Small changes in placement can add subtle emphasis (e.g. putting φέτος early stresses “this year” a bit more), but the basic meaning remains.

Εφέτος is a more formal / old-fashioned variant of φέτος. In everyday speech, φέτος is far more common.

Why is the adjective μεγάλη and not μεγάλο or something else? What exactly does μεγάλη mean here?

Μεγάλη is the feminine form of the adjective μεγάλος (big / great / large).

Μεγάλη here is feminine, singular, nominative, to agree with the subject η πιθανότητα (also feminine, singular, nominative).
The structure is:
[Η πιθανότητα] [είναι] [μεγάλη].
subject – linking verb – predicate adjective.

Meaning-wise:

Literally: the probability is big.
In English we usually say “the probability is high”, but Greek often uses μεγάλη (big/great) to express a large degree of probability.

More precise / formal alternatives:

Η πιθανότητα … είναι υψηλή. (high) – sounds more technical/formal than μεγάλη.
You can also intensify: είναι πολύ μεγάλη (is very high).

Could we say Η μεγάλη πιθανότητα να έχουμε επιτυχία φέτος… instead of …είναι μεγάλη? What’s the difference?

Yes, but the structure and emphasis change:

Original sentence:
Η πιθανότητα να έχουμε επιτυχία φέτος είναι μεγάλη.
- Μεγάλη is a predicate adjective linked with είναι.
- You are making a statement about the size of the probability.
Alternative:
Η μεγάλη πιθανότητα να έχουμε επιτυχία φέτος μας ενθαρρύνει.
(The high probability that we’ll succeed this year encourages us.)
- Here μεγάλη is an attributive adjective modifying πιθανότητα directly.
- You’d usually continue with something, because now “the high probability” becomes a full noun phrase that does something (encourages us, μας χαροποιεί, etc.).

So grammatically both uses of μεγάλη are fine, but the original sentence specifically equates the probability with being high, while the second kind of structure uses “the high probability” as a starting point for another statement.

How flexible is the word order in this sentence? Can we move parts like φέτος or είναι μεγάλη around?

Greek word order is quite flexible, especially for elements like time adverbs and for emphasis. All of these are grammatical:

Η πιθανότητα να έχουμε επιτυχία φέτος είναι μεγάλη.
Η πιθανότητα να έχουμε φέτος επιτυχία είναι μεγάλη.
Η πιθανότητα φέτος να έχουμε επιτυχία είναι μεγάλη.
Φέτος η πιθανότητα να έχουμε επιτυχία είναι μεγάλη.

Main points:

The core structure (subject–verb–predicate adjective) must remain clear:
Η πιθανότητα … είναι μεγάλη.
Moving φέτος changes emphasis slightly:
- Sentence 4, starting with Φέτος, puts extra focus on “this year”:
  As for this year, the probability that we’ll succeed is high.
You could also (especially in speech) say:
Η πιθανότητα είναι μεγάλη να έχουμε επιτυχία φέτος.
This still works, just shifts the weight more onto “the probability is high” as a chunk.

The sentence is quite tolerant to reordering as long as the relationships between words stay clear.

In English we might say “the probability that we’ll succeed”. Why doesn’t Greek use ότι or που, and why do we have να instead?

In Greek, after πιθανότητα, the usual way to introduce a clause about what may happen is να + subjunctive, not ότι or που.

Compare:

Η πιθανότητα να έχουμε επιτυχία φέτος είναι μεγάλη.
(Standard, natural Greek.)

Using ότι:

Η πιθανότητα ότι θα έχουμε επιτυχία φέτος είναι μεγάλη.
This sounds unnatural or like a calque from English; it’s not how native speakers normally phrase it.

Using που is also not standard here.

So the pattern you should learn is:

η πιθανότητα να + [subjunctive]
- η πιθανότητα να βρέξει (probability that it will rain)
- η πιθανότητα να έρθει (probability that he/she will come)

Να is the normal conjunction here; it both introduces the clause and signals the subjunctive mood.

Could we drop να έχουμε and just say Η πιθανότητα επιτυχίας φέτος είναι μεγάλη? Is that correct and does it mean the same?

Yes, that is correct and very natural:

Η πιθανότητα επιτυχίας φέτος είναι μεγάλη.

Here:

Επιτυχίας is the genitive singular of επιτυχία.
The phrase πιθανότητα επιτυχίας means probability of success.

Meaning-wise it’s practically the same:

Η πιθανότητα να έχουμε επιτυχία φέτος είναι μεγάλη.
Η πιθανότητα επιτυχίας φέτος είναι μεγάλη.

The version with επιτυχίας feels slightly more compact and somewhat more formal / written, like something you might see in reports, articles, or more careful speech.

The να έχουμε επιτυχία version sounds very normal in both speech and writing and leaves the subject “we” explicit.

Is this whole sentence more formal, informal, or neutral? How would it typically be used?

The sentence:

Η πιθανότητα να έχουμε επιτυχία φέτος είναι μεγάλη.

is neutral, perfectly fine in:

everyday conversation,
news reports,
presentations,
written texts.

If you wanted it to sound more formal/technical, you might choose:

Η πιθανότητα επιτυχίας φέτος είναι υψηλή.
Οι πιθανότητες επιτυχίας φέτος είναι υψηλές.

Using υψηλή/υψηλές instead of μεγάλη/μεγάλες and the genitive επιτυχίας gives it a slightly more scientific or professional tone.