Learn Hardcore Greek: Με αυτόν τον σταθερό ρυθμό νιώθω ότι η εξέλιξή μου είναι σίγουρη. - With this steady rhythm I feel that my progress is certain.

Using αυτός (nominative) after με would be ungrammatical in Modern Greek. αυτό is neuter, so it would also be wrong, because it must agree in gender and case with ρυθμό, which is masculine accusative.

Why are there two words, αυτόν and τον, before ρυθμό? Isn’t one article enough?

In Modern Greek, demonstratives like αυτός / εκείνος usually appear together with the definite article when used attributively (before a noun).

Pattern:

αυτός ο ρυθμός = this pace
εκείνος ο ρυθμός = that pace

In the accusative:

με αυτόν τον ρυθμό = with this pace
με εκείνον τον ρυθμό = with that pace

So αυτόν is the demonstrative (this), and τον is just the normal definite article (the). Both are needed in standard usage.

Why is it τον σταθερό ρυθμό and not τον ρυθμό σταθερό? Where do adjectives usually go?

The most common position for adjectives in Greek is before the noun, between the article and the noun:

τον σταθερό ρυθμό = the steady pace

This is called the attributive position:
άρθρο + επίθετο + ουσιαστικό → τον σταθερό ρυθμό

You can also put the adjective after the noun in another attributive pattern:

τον ρυθμό τον σταθερό

This is grammatical but more emphatic or stylistic, something like the pace, the steady one. The neutral, everyday word order is the one in your sentence: τον σταθερό ρυθμό.

What is the nuance of ρυθμός here? Is it “rhythm” or “speed”?

Ρυθμός literally means rhythm, but it’s very commonly used for:

pace / rate (how steadily and regularly something is progressing)

So με αυτόν τον σταθερό ρυθμό is best understood as:

at this steady pace
with this consistent rate (of work / study / progress)

If you said ταχύτητα, that would be closer to raw speed (fast/slow), whereas ρυθμός suggests a regular, stable pattern of progress.

What’s the difference between νιώθω, αισθάνομαι, and νομίζω when I want to say “I feel that…”?

In this sentence, νιώθω ότι… means I feel that… in the sense of an inner feeling or impression.

νιώθω – literally I feel, often emotional/physical or a gut sense.
- νιώθω ότι… ≈ I feel that… (subjective impression).
αισθάνομαι – more formal, very close to νιώθω, often interchangeable in many contexts.
- αισθάνομαι ότι… sounds slightly more formal or careful.
νομίζω – I think / I believe (intellectual opinion rather than feeling).
- νομίζω ότι… = I think that…

In your sentence, νιώθω ότι η εξέλιξή μου είναι σίγουρη emphasises an internal sense or confidence, not just a rational conclusion.

What does ότι do here? Can I replace it with πως or drop it like English often drops “that”?

Ότι is a subordinating conjunction meaning that, introducing a clause:

νιώθω ότι η εξέλιξή μου είναι σίγουρη
= I feel that my progress is certain.

About your options:

Replace with πως:
- νιώθω πως η εξέλιξή μου είναι σίγουρη
  This is also correct and quite natural in everyday speech.
Drop it completely:
- νιώθω η εξέλιξή μου είναι σίγουρη
  This is not standard in Modern Greek. Unlike English, Greek normally keeps ότι/πως in this structure.

So you can safely use either ότι or πως, but you should not omit it.

What exactly does η εξέλιξή μου mean? Is it “evolution” or “progress”? And why is it feminine?

Εξέλιξη is a feminine noun. Its main meanings include:

development, progress, advancement (of a person, project, skill, etc.)
evolution (biological or metaphorical)
unfolding of events (the course, the way things develop)

Here:

η εξέλιξή μου = my progress / my development (as a learner, person, etc.)

Why feminine? Nouns in Greek have grammatical gender that you usually just have to learn with the noun:

η εξέλιξη (feminine)
της εξέλιξης (genitive singular)
την εξέλιξη (accusative singular)

The article η shows it’s feminine in the nominative.

Why is there an accent on εξέλιξή (η εξέλιξή μου) but not on μου? And why does the accent seem to move?

The base form is:

η εξέλιξη (stress on -ξέ-)

When you add a clitic pronoun like μου (my), Greek stress rules require the accent to stay within the last three syllables of the whole group. To satisfy that, the written accent is repeated on the noun:

η εξέλιξή μου

You see the accent on the last syllable (-ξή), but you should understand this as a phonological group: εξέλιξή μου. The clitic μου never takes its own accent; instead, the noun adjusts its accent so the whole phrase is pronounced correctly.

So:

η εξέλιξη
η εξέλιξή μου
η εξέλιξή σου, etc.

This is a regular pattern with nouns + enclitic pronouns.

Why is it η εξέλιξή μου and not η μου εξέλιξη, like English “my progress”?

In Modern Greek, the “weak” possessive pronouns (μου, σου, του, της, μας, σας, τους) usually go after the noun:

η εξέλιξή μου = my progress
το σπίτι σου = your house
το παιδί μας = our child

The form η μου εξέλιξη is:

very unusual in Modern Greek,
feels archaic or poetic,
not what you use in everyday language.

So the natural order is article + noun (+ adjective) + possessive clitic.

Why is it είναι σίγουρη and not είμαι σίγουρος? What is the subject of είναι?

The subject of είναι is η εξέλιξή μου (my progress), not the speaker.

So the structure is:

η εξέλιξή μου (subject)
είναι (3rd person singular of to be)
σίγουρη (predicate adjective, agreeing with the subject)

Literal structure:

my progress is certain

If you said είμαι σίγουρος, the subject would be I (the speaker):

Είμαι σίγουρος ότι η εξέλιξή μου είναι σίγουρη.
= I am sure that my progress is certain.

In the given sentence, we are not describing how sure I am; we are describing how certain my progress is (from my point of view).

Why is the adjective σίγουρη (feminine) and not σίγουρος or σίγουρο?

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

Noun: η εξέλιξή μου
- Gender: feminine
- Number: singular
- Case: nominative (subject)

So the adjective must also be:

feminine, singular, nominative → σίγουρη

Forms of the adjective σίγουρος (sure, certain):

masculine: σίγουρος
feminine: σίγουρη
neuter: σίγουρο

Even if the speaker is male, the adjective here agrees with εξέλιξη (a feminine noun), not with the speaker.

Could I change the word order? For example, can I say Νιώθω ότι η εξέλιξή μου είναι σίγουρη με αυτόν τον σταθερό ρυθμό?

Yes, Greek word order is relatively flexible, especially for adverbial phrases like με αυτόν τον σταθερό ρυθμό.

Your alternative:

Νιώθω ότι η εξέλιξή μου είναι σίγουρη με αυτόν τον σταθερό ρυθμό.

is grammatical and understandable. The difference is mainly one of emphasis:

Με αυτόν τον σταθερό ρυθμό νιώθω ότι η εξέλιξή μου είναι σίγουρη.
– Fronts the pace, emphasising it: At this steady pace, I feel that my progress is certain.
Νιώθω ότι η εξέλιξή μου είναι σίγουρη με αυτόν τον σταθερό ρυθμό.
– Starts from the feeling and adds the pace as extra information at the end.

Both are fine; the original sentence slightly highlights the pace as the frame or condition for the feeling.