Learn Hardcore Greek: Πιστεύεται ότι η καθημερινή επανάληψη είναι ο πιο αποτελεσματικός τρόπος για πρόοδο. - It is believed that daily revision is the most effective way for progress.

There is no specific person mentioned (like “they” or “people”).
The “subject” of πιστεύεται is the whole ότι-clause that follows:
- Πιστεύεται ότι η καθημερινή επανάληψη…
  = It is believed that daily repetition…

This is called an impersonal passive construction. In English we often translate it either as:

It is believed that daily repetition is…, or
People believe that daily repetition is… (more natural English, but slightly less formal/impersonal).

Why does Greek use the passive Πιστεύεται instead of an active form like “People believe that…”?

Greek often uses the impersonal passive to express general opinions or commonly held beliefs in a neutral, objective way.

Compare:

Πιστεύεται ότι η καθημερινή επανάληψη είναι…
= It is believed that daily repetition is…
(impersonal, formal, objective tone)
Πολλοί πιστεύουν ότι η καθημερινή επανάληψη είναι…
= Many people believe that daily repetition is…
(active, explicitly mentions “many people”)

Both are correct, but:

The passive impersonal form (Πιστεύεται ότι…) sounds more formal, bookish, or academic.
The active form (Πολλοί πιστεύουν ότι…) sounds more conversational and direct.

What is the role of ότι here, and what’s the difference between ότι, πως, and να?

In this sentence, ότι introduces a content clause — a statement that functions as the object/subject of πιστεύεται:

Πιστεύεται ότι η καθημερινή επανάληψη είναι…
= It is believed that daily repetition is…

Differences:

ότι and πως
- Both can mean “that” (introducing a reported statement).
- Πιστεύεται ότι… and Πιστεύεται πως… are both acceptable.
- ότι is slightly more formal and clearer in writing.
- πως can be a bit more informal or conversational in many contexts.
να
- να does not mean “that” here.
- It typically introduces subjunctive verbs and purpose/desired actions:
  - Θέλω να διαβάζω κάθε μέρα. = I want to study every day.
- You cannot say ✗ Πιστεύεται να η καθημερινή επανάληψη είναι… — that is ungrammatical.
- With verbs of saying/thinking/believing, when you report a factual statement, you use ότι/πως, not να.

Why does the phrase η καθημερινή επανάληψη have the article η? Isn’t it talking about repetition in general?

Yes, it talks about repetition in general, but Greek often uses the definite article with generic or abstract nouns, especially when they are subjects.

η καθημερινή επανάληψη
literally: the daily repetition, but functionally: daily repetition (in general).

In Greek:

Generic subjects are very often introduced with the article:
- Η αγάπη είναι σημαντική.
  = Love is important.
- Η μουσική μας βοηθάει.
  = Music helps us.
Similarly, Η καθημερινή επανάληψη είναι… = Daily repetition is…

You could in theory say Καθημερινή επανάληψη είναι…, but without the article it sounds less natural, a bit telegraphic or headline-like.
In standard speech and writing, η καθημερινή επανάληψη is the normal choice.

Why is καθημερινή placed before επανάληψη? Could we say η επανάληψη καθημερινή instead?

In η καθημερινή επανάληψη, καθημερινή is an adjective in attributive position, directly modifying the noun:

η καθημερινή επανάληψη = the daily repetition

Basic patterns for adjectives in Greek:

Attributive position (normal “adjective before noun” pattern)
- η καθημερινή επανάληψη = the daily repetition
- ο καλός άνθρωπος = the good person
Predicate position (after a form of “to be”, describing the subject)
- Η επανάληψη είναι καθημερινή. = The repetition is daily.
- Ο άνθρωπος είναι καλός. = The person is good.

If you say η επανάληψη καθημερινή with no verb, it sounds incomplete or poetic/elliptical.
So in this sentence, the normal, grammatical form is η καθημερινή επανάληψη.

The subject η καθημερινή επανάληψη is feminine. Why do we suddenly get ο πιο αποτελεσματικός τρόπος (masculine)? Shouldn’t everything agree?

The key is to see what the adjective αποτελεσματικός is agreeing with.

Structure:

η καθημερινή επανάληψη (feminine) = daily repetition (subject)
είναι = is
ο πιο αποτελεσματικός τρόπος (masculine) = the most effective way (predicate noun phrase)

So the verb είναι links:

Subject: η καθημερινή επανάληψη
Complement (predicate nominative): ο πιο αποτελεσματικός τρόπος

The adjective αποτελεσματικός doesn’t have to match the subject; it must match the noun it modifies, which is τρόπος (masculine):

ο τρόπος (masculine article)
αποτελεσματικός (masculine adjective)

Hence:

ο πιο αποτελεσματικός τρόπος = the most effective way

This is just like English:

Daily repetition is the most effective way.
- Subject: daily repetition
- Complement: the most effective way

You would not say:

✗ η πιο αποτελεσματική τρόπος — incorrect, because τρόπος is masculine, not feminine.

How does ο πιο αποτελεσματικός express “the most effective”? Is this comparative or superlative? What about αποτελεσματικότερος?

Modern Greek mostly uses a periphrastic (two-word) form with πιο:

πιο αποτελεσματικός = more effective (comparative)
ο πιο αποτελεσματικός = the most effective (superlative, because of the definite article ο)

So in context:

ο πιο αποτελεσματικός τρόπος
= the most effective way

There are also synthetic forms:

αποτελεσματικότερος = more effective / most effective
ο αποτελεσματικότερος τρόπος = the most effective way

However:

In everyday modern Greek, πιο + adjective is far more common than the synthetic form.
ο πιο αποτελεσματικός τρόπος sounds natural and common.
ο αποτελεσματικότερος τρόπος sounds more formal, literary, or old‑fashioned, though it is correct.

Why is there no article before πρόοδο? Why not για την πρόοδο?

Here, πρόοδο is the accusative singular of η πρόοδος (progress).

για πρόοδο = for progress (in general)
⇒ no article, abstract/general meaning.

Greek often drops the article with abstract nouns when they are used in a very general, non‑specific way, especially in certain prepositional phrases.

Compare:

για πρόοδο = for progress (in general)
για την πρόοδο του έργου = for the progress of the project
(now it’s a specific kind of progress; you use την
- extra information)

So in this sentence we’re talking about progress generally, not the progress of a particular thing, which is why we say για πρόοδο, without the article.

What exactly does για mean here in για πρόοδο? How is για πρόοδο different from για να κάνεις πρόοδο?

In this context, για with a noun in the accusative indicates purpose or goal:

για πρόοδο = for progress / aimed at progress

You could express a similar idea with a verb phrase:

για να κάνεις πρόοδο = in order for you to make progress
για να υπάρξει πρόοδος = in order for there to be progress

Differences:

για πρόοδο
- Uses a noun (πρόοδο).
- Stays more compact and abstract: “for progress”.
για να κάνεις πρόοδο
- Uses για να + subjunctive verb (κάνεις).
- Emphasizes the action of making progress and often implies a subject (“you”, “someone”).

In the original sentence, για πρόοδο keeps the statement short and general:
the most effective way for progress.

Can we say η επανάληψη κάθε μέρα instead of η καθημερινή επανάληψη? Is there any difference?

Yes, both are possible, but they differ slightly in style and structure.

η καθημερινή επανάληψη
- Adjective καθημερινή directly modifies επανάληψη.
- Very compact, sounds a bit more formal or “slogan-like”.
- Literally: the daily repetition.
η επανάληψη κάθε μέρα
- Literally: the repetition every day.
- Feels a bit more conversational and explicit about the time frame.
- Could be rephrased in English as repeating every day.

Both are grammatically correct. In a more formal, general statement like this one, η καθημερινή επανάληψη is slightly more typical.

Could the word order be changed, for example Η καθημερινή επανάληψη πιστεύεται ότι είναι…? Does that sound natural?

Yes, Greek word order is relatively flexible, and you can move things around, but the naturalness changes.

Possible variants:

Πιστεύεται ότι η καθημερινή επανάληψη είναι ο πιο αποτελεσματικός τρόπος για πρόοδο.
- Very natural, neutral word order.
- Starts with the impersonal verb Πιστεύεται, then the ότι‑clause.
Η καθημερινή επανάληψη πιστεύεται ότι είναι ο πιο αποτελεσματικός τρόπος για πρόοδο.
- Also grammatical.
- Slightly shifts the focus to η καθημερινή επανάληψη as the first element.
- Can sound a bit more formal or stylistically marked.
Πιστεύεται πως η καθημερινή επανάληψη είναι ο πιο αποτελεσματικός τρόπος για πρόοδο.
- Same meaning, with πως instead of ότι.
- Common and natural, perhaps a touch more conversational.

All of these are acceptable; the original version is probably the most neutral and typical in written standard Greek.

What are the cases of επανάληψη and πρόοδο here, and how can I recognize them?

Both words are in the singular, but in different cases:

η καθημερινή επανάληψη
- Noun: επανάληψη (repetition)
- Article: η
- Case: nominative singular (subject of the sentence)
- Pattern: η επανάληψη (nom.), της επανάληψης (gen.), την επανάληψη (acc.)
για πρόοδο
- Noun: πρόοδο (from η πρόοδος, progress)
- No article here.
- Case: accusative singular, because για takes the accusative.
- Pattern: η πρόοδος (nom.), της προόδου (gen.), την πρόοδο (acc.)

Key hints:

Feminine nouns ending in ‑η / ‑ηψη / ‑ση (like επανάληψη) have accusative singular in ‑η / ‑ηψη / ‑ση (same spelling, different article).
Feminine nouns in ‑ος (like πρόοδος) usually have accusative singular in ‑ο (πρόοδο).