Learn Hardcore Greek: Κανείς δεν είναι εδώ τώρα.

Greek uses what’s called negative concord: multiple negative elements work together to express one negation, not to cancel each other out.
In this sentence, κανείς is a negative/indefinite pronoun (“no one / nobody”), and δεν is the normal verb negator (“not”).
So Κανείς δεν είναι εδώ τώρα literally has “no one” + “not is”, but the meaning is still just “no one is here now”, not “everyone is here now”.
If you remove δεν, the sentence becomes ungrammatical; you can’t say ✱Κανείς είναι εδώ τώρα to mean “no one is here now”.
In Greek, when you use κανείς with a verb, you almost always need δεν (or another negative like μην) in the same clause for the “nobody” meaning in statements.

Can κανείς also mean “anyone”, or does it always mean “no one”?

κανείς can mean “no one / nobody” or “anyone”, depending on the context.

With δεν or other negatives, it means “no one”:
- Κανείς δεν είναι εδώ. → “No one is here.”
In questions, conditional clauses, or some other non-negative contexts, it usually means “anyone”:
- Είναι κανείς εδώ; → “Is anyone here?”
- Ξέρει κανείς; → “Does anyone know?”

So the same word switches between “no one” and “anyone” based on whether the clause is negative or not.

What’s the difference between κανείς and κανένας? Could I say Κανένας δεν είναι εδώ τώρα instead?

κανείς and κανένας are forms of the same pronoun; both can be masculine nominative singular.
You can say Κανένας δεν είναι εδώ τώρα, and it’s very natural in everyday speech; many speakers actually use κανένας more often in conversation.

Some rough tendencies:

κανείς: slightly more neutral / careful / written, but also common in speech.
κανένας: often more colloquial, very common in spoken language.

Both mean “no one / anyone” (depending on context). In your example sentence, Κανείς δεν είναι εδώ τώρα and Κανένας δεν είναι εδώ τώρα are functionally equivalent in meaning.

What grammatical role does κανείς have here, and what case is it?

In Κανείς δεν είναι εδώ τώρα, κανείς is the subject of the verb είναι (“is”).
Since it’s the subject, it’s in the nominative case: masculine nominative singular.
You can think of it as standing for something like “no person” functioning as “he/they” in English:

Κανείς (subject) δεν είναι (verb) εδώ (place) τώρα (time).

Why is the verb είναι singular? In English “no one” feels kind of plural in meaning.

In Greek, κανείς is grammatically singular, so the verb agrees and is also singular: είναι (“is”).
Even though logically we’re talking about “zero people”, the grammar treats it like one indefinite person that doesn’t exist.
So you always use a singular verb with κανείς / κανένας in this subject position:

Κανείς δεν είναι εδώ. (“No one is here.”)
Κανένας δεν ήρθε. (“No one came.”)

Is the word order fixed? Could I say Δεν είναι κανείς εδώ τώρα instead?

The word order is not fixed; several orders are possible and grammatical.
Common variants include:

Κανείς δεν είναι εδώ τώρα.
Δεν είναι κανείς εδώ τώρα.

Both mean essentially the same thing: “No one is here now.”
Placing κανείς at the beginning (Κανείς δεν είναι…) slightly emphasizes “no one” as the topic.
Placing δεν είναι first (Δεν είναι κανείς…) can feel a bit more neutral, like “There isn’t anyone here now.”
In everyday speech, Δεν είναι κανείς εδώ (τώρα) is extremely common.

Why is it εδώ τώρα and not τώρα εδώ? Do both orders work?

Both εδώ τώρα and τώρα εδώ are grammatically possible.
In this specific sentence, εδώ τώρα (“here now”) is the most natural-sounding neutral order.

Very roughly:

εδώ τώρα = “here now” (plain statement of place + time).
τώρα εδώ can sound a bit more contrastive, like “now, (we’re) here” as opposed to some other time or place, depending on context and intonation.

So Κανείς δεν είναι εδώ τώρα is the most typical, neutral way to say it, but Κανείς δεν είναι τώρα εδώ is also possible, with a small shift in emphasis to “at this time”.

Can I leave out εδώ or τώρα? How does the meaning change?

Yes, you can omit either adverb, and the sentence stays grammatical:

Κανείς δεν είναι εδώ. → “No one is here.” (no mention of time)
Κανείς δεν είναι τώρα εδώ. or Τώρα δεν είναι κανείς εδώ. → “(Right) now, no one is here.” (time is stressed more than place)

Leaving out εδώ removes the information about place; leaving out τώρα removes the information about time.
Native speakers often shorten sentences like this depending on what’s obvious from context.

How would I turn this into a question meaning “Is anyone here now?”

To say “Is anyone here now?”, you normally remove the negation and use κανείς (or κανένας) in a question:

Είναι κανείς εδώ τώρα;
Είναι κανένας εδώ τώρα; (a bit more colloquial)

Notice there is no δεν in the question form.
Here κανείς / κανένας is understood as “anyone”, because it appears in a non-negative question.

Are there feminine or neuter forms related to κανείς / κανένας?

Yes. κανείς / κανένας is the masculine form, but the same pronoun has feminine and neuter forms too.
In the nominative singular:

Masculine: κανείς / κανένας
Feminine: καμία / καμιά
Neuter: κανένα

For “no one” in the general sense (without specifying gender), Greek normally uses the masculine form as a generic, which is why we say Κανείς δεν είναι εδώ τώρα even if we’re talking about people of any gender.

How do I pronounce Κανείς δεν είναι εδώ τώρα? Where is the stress?

Syllable breakdown with stress (marked by the written accent):

Κανείς → κα-νείς [ka-NEES]
δεν → δεν [then / ðen]
είναι → εί-ναι [EE-neh / ˈi.ne]
εδώ → ε-δώ [e-THÓ / eˈðo]
τώρα → τώ-ρα [TÓ-ra / ˈtora]

Natural speech will connect the words smoothly:
[kaˈnis ðen ˈine eˈðo ˈtora].
Make sure to put the main stress on the accented syllable of each word and to pronounce δ as the voiced “th” sound (like in this, not like thin).