Learn Hardcore Greek: Αν βήχεις πολύ, πρέπει να πας σε γιατρό. - If you cough a lot, you must go to a doctor.

Αν is the everyday, neutral form of εάν.
Εάν is a bit more formal or careful (you’ll see it more in writing, instructions, news, etc.).
Άμα is more colloquial and spoken, like “if/when” in casual speech.

In this sentence, you could also hear:

Εάν βήχεις πολύ, πρέπει να πας σε γιατρό. (more formal)
Άμα βήχεις πολύ, πρέπει να πας σε γιατρό. (more informal)

All three work; αν is the default in everyday standard Greek.

How is βήχεις formed, and what verb is it from?

Βήχεις is the 2nd person singular, present tense, indicative of the verb βήχω = “to cough”.

Full present-tense conjugation (informal standard):

εγώ βήχω – I cough
εσύ βήχεις – you cough
αυτός/αυτή/αυτό βήχει – he/she/it coughs
εμείς βήχουμε – we cough
εσείς βήχετε – you (plural/polite) cough
αυτοί/αυτές/αυτά βήχουν(ε) – they cough

So αν βήχεις literally = “if you cough”.

How do you pronounce βήχεις, and why is it spelled with η and ει?

Pronunciation: βήχεις is pronounced approximately [VEE-khis], in IPA [ˈvixis].

β = v
ή (eta with accent) = /i/ like the ee in see
χ before ει is a voiceless palatal fricative, something like the h in huge but stronger (not exactly English)
ει also = /i/

So both η and ει sound like /i/ in Modern Greek; the spelling is historical.

Stress: the accent ή shows the stress: ΒΗ‑χεις (stress on the first syllable).

Why is it βήχεις (present) and not some future tense like “will cough”?

Greek often uses the present tense in the if‑clause to talk about a general condition:

Αν βήχεις πολύ…
Literally: “If you cough a lot…”
Meaning: whenever that situation is true, under that condition.

English might also say:

“If you are coughing a lot…”
“If you cough a lot…”

You normally don’t use the future (θα βήξεις) after αν in this kind of general rule.
So: αν + present = “if (ever/whenever) …”, a general condition.

Why is it πολύ and not πολύς or something similar?

Πολύ here is an adverb, modifying the verb βήχεις:

βήχεις πολύ = you cough a lot / you cough very much

Compare:

πολύ (adverb) – a lot, very much
- Μαγειρεύει πολύ. – She cooks a lot / very much.
πολύς / πολλή / πολύ (adjective) – much / many / a lot of
- πολύς βήχας – a lot of cough(ing)
- πολλά φάρμακα – many medicines

In αν βήχεις πολύ, we describe how much you cough, so the adverb πολύ is correct.

What does πρέπει να mean exactly? Is it “must” or “should”?

Πρέπει να is an impersonal modal expression meaning “must / have to / should / ought to.”

πρέπει να πας ≈ you must go / you have to go / you should go

Nuance:

In many everyday contexts, πρέπει να can be strong advice rather than a strict obligation, much like “you really should go to a doctor.”
Grammatically, πρέπει is always 3rd person singular and impersonal; the real “subject” is the να‑clause:
- Πρέπει [να πας σε γιατρό].
  Literally: “It is necessary [that you go to a doctor].”

What form of the verb is να πας, and why not just πας or πηγαίνεις?

Να πας is a subjunctive form (called the “να + subjunctive” in Modern Greek). It’s used:

after certain verbs/expressions like πρέπει, θέλω, μπορώ
to express purpose, necessity, wish, possibility, etc.

Here:

πρέπει να πας = you must (go).

Why not just πας?
In Modern Greek, after πρέπει you must use να + verb:

✔ Πρέπει να πας.
✘ Πρέπει πας.

Why not να πηγαίνεις?

να πας (aorist subjunctive) views the action as one complete event – “you should go (once).”
να πηγαίνεις (imperfective subjunctive) would suggest ongoing / repeated action – “you should be going (regularly / habitually),” which doesn’t fit as well here.

So in this context, να πας is the natural choice.

Why is it σε γιατρό and not στον γιατρό?

Both are grammatically correct, but there’s a nuance:

σε γιατρό = to a doctor (any doctor, indefinite)
στον γιατρό = to the doctor (more specific: your doctor, the one we both know, or “the doctor” in this context)

Details:

σε + τον → στον (preposition + definite article)
σε γιατρό has no article, so it’s more general/indefinite.

In this sentence, we are giving a general piece of advice:
“If you cough a lot, you should go to a doctor (some doctor, not a particular one).”
That’s why σε γιατρό sounds very natural.

Could we say σε έναν γιατρό instead of σε γιατρό?

Yes, you can say:

Αν βήχεις πολύ, πρέπει να πας σε έναν γιατρό.

This is perfectly correct and means “to a (certain) doctor.”

Nuance:

σε γιατρό – very general, any doctor, typical in advice.
σε έναν γιατρό – still indefinite, but it can sound a bit more like “to some doctor (one doctor in particular)”, slightly more specific.

In everyday speech, people often omit the indefinite article after σε with professions:

Πάω σε γιατρό. – I’m going to a doctor.
Πάω σε δάσκαλο. – I’m going to a teacher/tutor.

What case and gender is γιατρό, and what is the basic dictionary form?

The dictionary form is ο γιατρός = “doctor” (masculine noun, but can refer to both male and female doctors in practice).

Cases (singular, masculine pattern):

Nominative: ο γιατρός – the doctor (subject)
Genitive: του γιατρού – of the doctor
Accusative: τον γιατρό – the doctor (object / after prepositions)

In σε γιατρό, γιατρό is accusative singular without an article. It’s the normal form after the preposition σε when you mean “to a doctor.”

Why is there a comma after πολύ? Could we change the word order?

The comma separates the if‑clause from the main clause:

Αν βήχεις πολύ, → condition
πρέπει να πας σε γιατρό. → result / consequence

This is standard punctuation when the if‑clause comes first.

You can change the word order and put the if‑clause at the end:

Πρέπει να πας σε γιατρό, αν βήχεις πολύ.

This is also correct and sounds natural. You still need the comma, because you’re separating the two clauses.

What you generally don’t do is put πολύ before the verb:

✘ Αν πολύ βήχεις – wrong word order
✔ Αν βήχεις πολύ – correct

Could we use όταν instead of αν here?

You could, but the meaning changes slightly:

Αν βήχεις πολύ, πρέπει να πας σε γιατρό.
= If you cough a lot (on the condition that you do), you should go to a doctor.
Όταν βήχεις πολύ, πρέπει να πας σε γιατρό.
= When(ever) you cough a lot, you should go to a doctor.

Όταν focuses more on time / whenever it happens, while αν focuses on a condition.

In practice, in advice like this, αν is the more typical and neutral choice.

Could we say something like πρέπει να δεις έναν γιατρό instead of πρέπει να πας σε γιατρό? Is there any difference?

Yes:

Πρέπει να πας σε γιατρό. = You must / should go to a doctor.
Πρέπει να δεις έναν γιατρό. = You must / should see a doctor.

Both are idiomatic and very common.
Nuance:

να πας σε γιατρό emphasizes going (the visit).
να δεις έναν γιατρό emphasizes seeing / consulting the doctor.

In everyday speech they’re practically interchangeable in this context of giving health advice.