Learn Hardcore Greek: Κάποιος χτυπάει την πόρτα τώρα.

It usually corresponds to “someone” in a positive statement:
- Κάποιος χτυπάει την πόρτα. = Someone is knocking at the door.
It is not the same as “anyone” in questions/negatives; for those Greek normally uses κανείς:
- Χτυπάει κανείς την πόρτα; = Is anyone knocking at the door?
- Δεν χτυπάει κανείς την πόρτα. = No one is knocking at the door.

So in this sentence, κάποιος = “some person (unknown who)”.

Why is it χτυπάει and not χτυπά? Are both correct? What’s the difference?

Both χτυπάει and χτυπά are correct present tense 3rd person singular forms of the verb χτυπάω / χτυπώ (to knock, to hit).

χτυπάει is the more colloquial / everyday spoken form.
χτυπά is a bit shorter and slightly more formal / written, but you also hear it in speech.

Meaning-wise in modern Greek, there is no difference here:

Κάποιος χτυπάει την πόρτα.
Κάποιος χτυπά την πόρτα.
Both mean “Someone is knocking at the door.”

Does χτυπάει mean “is knocking” or “knocks”? How does the Greek present compare to English?

Greek present tense usually covers both English present simple and present continuous.

Κάποιος χτυπάει την πόρτα τώρα.
- can correspond to:
  - Someone is knocking at the door now. (continuous)
  - Someone knocks at the door now. (less natural in English, but grammatically present simple)

In actual use here, because of τώρα (now), English prefers the continuous:
“Someone is knocking at the door now.”

Greek does not need a special continuous form; the simple present (χτυπάει) already expresses a present, ongoing action.

Why is it την πόρτα and not just πόρτα? What is that την?

Την is the definite article (“the”), in the accusative feminine singular.

Nominative: η πόρτα = the door (subject)
Accusative: την πόρτα = the door (object)

Greek normally uses the definite article much more consistently than English. Here, την πόρτα = “the door”, the specific door you’re talking about (e.g. the door of the house/room you're in).

So:

Κάποιος χτυπάει την πόρτα. = Someone is knocking (on) the door.

Dropping the article (Κάποιος χτυπάει πόρτα) is not normal in standard Greek here.

Why is there no word for “at” like “στην” before πόρτα? English says “at the door”.

English uses a preposition: “at the door”.
Greek instead uses a direct object with the verb χτυπάω:

χτυπάω την πόρτα = literally “I knock the door.”

The idea “on / at the door” is built into the verb χτυπάω in this context, so you do not say:

✗ χτυπάω στην πόρτα (this sounds wrong or at least unnatural for knocking).

So:

Κάποιος χτυπάει την πόρτα τώρα. = Someone is knocking at the door now.

What case is την πόρτα in, and why?

Την πόρτα is in the accusative case.

Greek uses accusative for the direct object of a verb.
In this sentence, πόρτα is the thing being knocked:
Κάποιος (subject, nominative) χτυπάει (verb) την πόρτα (direct object, accusative).

So the article and noun both change:

η πόρτα → την πόρτα (nominative → accusative).

Can τώρα only go at the end of the sentence? Could I say it elsewhere?

No, τώρα (now) is flexible. All of these are possible:

Τώρα κάποιος χτυπάει την πόρτα.
Κάποιος τώρα χτυπάει την πόρτα.
Κάποιος χτυπάει τώρα την πόρτα.
Κάποιος χτυπάει την πόρτα τώρα.

They all mean essentially the same: “Someone is knocking at the door now.”
Putting τώρα at the beginning (Τώρα…) can add a little emphasis to “now”, but in everyday speech the difference is small.

Is κάποιος grammatically masculine? What if the person is a woman?

Yes, κάποιος is the masculine form, but in many contexts it is used generically, like English “someone”, regardless of gender.

Forms:

Masculine: κάποιος
Feminine: κάποια
Neuter: κάποιο

If you specifically wanted a female person, you could say:

Κάποια χτυπάει την πόρτα. = Some woman is knocking at the door.

But if you don’t know or don’t care about gender, you normally just say κάποιος.

Could I say this sentence without κάποιος, like just Χτυπάει την πόρτα τώρα?

Yes, you can say:

Χτυπάει την πόρτα τώρα.

In Greek, if the subject is obvious or not important, it is often left out. Here, dropping κάποιος makes the sentence a bit more like:

There’s knocking at the door now. / Someone is knocking at the door now.

You lose the explicit “someone”, but the meaning is still clear from context and the verb ending -ει (3rd person singular).

What’s the difference between χτυπάω and χτυπώ as dictionary forms?

Modern Greek verbs often come in two parallel forms:

χτυπάω (more colloquial)
χτυπώ (slightly more formal / old-fashioned style)

Conjugation in the 3rd person singular present:

(αυτός) χτυπάει / χτυπά (from χτυπάω)
(αυτός) χτυπά (from χτυπώ)

In everyday speech, people usually say χτυπάω / χτυπάει.
In more formal writing, you might see χτυπώ / χτυπά.
In this sentence, using χτυπάει is perfectly natural, spoken Greek.

Could I use κανείς instead of κάποιος in this sentence?

Not in this positive statement.

Κάποιος is used in positive sentences to mean someone.
Κανείς is typically used:
- in questions: anyone?
  - Χτυπάει κανείς την πόρτα; = Is anyone knocking at the door?
- with negation to mean no one:
  - Δεν χτυπάει κανείς την πόρτα. = No one is knocking at the door.

So here you must say:

Κάποιος χτυπάει την πόρτα τώρα.
not
✗ Κανείς χτυπάει την πόρτα τώρα.

Are there other natural ways to say “Someone is knocking at the door” in Greek?

Yes, a few common alternatives:

Κάποιος χτυπάει την πόρτα. (original, very standard)
Χτυπάει η πόρτα. = The door is knocking → idiomatic: Someone’s knocking.
Κάποιος είναι στην πόρτα. = Someone is at the door. (focuses on presence, not the noise)
Ακούς; Κάποιος χτυπάει την πόρτα. = Do you hear? Someone is knocking at the door.

All of these are natural, with slightly different focus (the sound, the door, or the person).