In short

A Greek conditional sentence has two halves: the υπόθεση (the αν-clause, the supposition) and the απόδοση (the main clause, the consequence). Which tenses go in each half depends on one thing only — how likely you consider the supposition. There are three patterns, and they are rigid enough to memorise as three lines:

Two rules never bend. θα never appears inside a conditional αν-clause — the αν itself carries the hypothetical meaning, so the θα stays in the main clause. (The other αν, the one that means “whether”, is not conditional at all and does take θα: Δεν ξέρω αν θα έρθει.) And αν negates with δεν, never with μην, because αν introduces an indicative, not a να-clause.

Concessive clauses (“although, even if”) split along the same real/unreal line: αν και, παρόλο που, μολονότι, ενώ, κι ας concede a fact; ακόμα κι αν, και να, όσο κι αν, ό,τι κι αν concede a supposition.

The rule

1. The open conditional. Use it when the supposition is a live possibility. The αν-clause takes an ordinary indicative — present for something habitual or already in progress, perfective non-past (the διαβάσω-form) for a single completed event. The main clause takes θα + future, a plain present (for general truths and habits), or an imperative.

Αν διαβάσεις, θα περάσεις. — Αν βρέχει, μένουμε σπίτι. — Αν τελειώσεις, φώναξέ με.

Note that the perfective non-past never stands alone in Greek: it needs θα, να, ας — or, as here, αν. That is why αν διαβάσεις is a complete, grammatical clause while διαβάσεις on its own is not.

2. Aspect inside the αν-clause. The present/perfective choice is the same aspect contrast you already know from θα and να; αν does not neutralise it.

• αν διαβάζεις — “if you are in the habit of studying / if you are studying (right now)”.
• αν διαβάσεις — “if you do the studying (once, and get through it)”.

3. The unreal present. When the supposition is contrary to fact now, or simply very unlikely, both halves go into the παρατατικός, and the main clause adds θα. English uses its past tense the same way (“if I had… I would…”).

Αν είχα λεφτά, θα ταξίδευα. — Αν ήξερα ελληνικά, θα δούλευα στην Αθήνα.

4. The unreal past. When the supposition is contrary to what actually happened, both halves go into the υπερσυντέλικος (είχα + απαρέμφατο-form), and the main clause again adds θα.

Αν είχα διαβάσει, θα είχα περάσει.

The two halves may be mixed when the sense demands it: a past supposition with a present result keeps the υπερσυντέλικος in the αν-clause and drops the main clause into the παρατατικός — Αν είχα φύγει νωρίτερα, τώρα θα ήμουν σπίτι.

5. Other conditional connectives. εάν is the formal written twin of αν and takes exactly the same tenses. άμα is its colloquial counterpart, and in speech it slides between “if” and “when”. σε περίπτωση που means “in the event that”, εκτός κι αν (or εκτός αν) means “unless”, and αρκεί να means “provided that, as long as” — this last one takes να, so it negates with μην.

6. Concessive clauses. A concessive grants something and then goes against it. The factual group (αν και, παρόλο που, μολονότι, ενώ, κι ας) presents the concession as true: Αν και είναι Αύγουστος, κάνει κρύο — it really is August. The hypothetical group (ακόμα κι αν, και να, όσο κι αν, ό,τι κι αν) presents it as a supposition, and behaves tense-wise exactly like the matching conditional: Ακόμα κι αν μου το ζητήσουν (open), Και να μου το ζητούσαν (unreal).

Because a concessive clause already contains the contrast, Greek does not add αλλά in the main clause. Where English tolerates “Although…, but…” in speech, Greek does not.

Forms & patterns

Pattern 1 — the open conditional (αν + perfective non-past of διαβάζω → θα + perfective non-past of περνάω)

Pattern 2 — the unreal present (αν + παρατατικός of έχω → θα + παρατατικός of ταξιδεύω; watch the stress move one syllable to the right in the 1st and 2nd plural, as the three-syllable rule requires: ταξίδευα → ταξιδεύαμε)

Pattern 3 — the unreal past (αν + υπερσυντέλικος → θα + υπερσυντέλικος; only the auxiliary έχω changes, the second part is invariable)

Aspect inside the αν-clause

Other conditional connectives

Concessives: factual against hypothetical

Negation follows the connective, not the meaning: αν, αν και, ακόμα κι αν, παρόλο που, ενώ all take δεν, while αρκεί να, και να, κι ας — all of them να/ας clauses — take μην.

Examples

Common mistakes

• Αν θα έρθεις, θα σου δείξω το σπίτι. -> Αν έρθεις, θα σου δείξω το σπίτι. — θα never enters the αν-clause; αν already marks the supposition, and the θα belongs to the result.
• Αν μην έρθεις, θα ανησυχήσω. -> Αν δεν έρθεις, θα ανησυχήσω. — αν introduces an indicative, so it negates with δεν. μην is for να- and ας-clauses (και να μην έρθεις, αρκεί να μην αργήσεις).
• Αν και ήταν κουρασμένος, αλλά δούλεψε ως αργά. -> Αν και ήταν κουρασμένος, δούλεψε ως αργά. — the concessive connective already carries the contrast; adding αλλά doubles it.
• Αν είχα λεφτά, θα ταξίδεψα στην Ασία. -> Αν είχα λεφτά, θα ταξίδευα στην Ασία. — the unreal present needs the παρατατικός on both sides; θα + αόριστος is not a Greek form here.
• Αν και δεν έρθει αύριο, θα ξεκινήσουμε. -> Ακόμα κι αν δεν έρθει αύριο, θα ξεκινήσουμε. — αν και concedes something you treat as a fact; for a supposition use ακόμα κι αν or και να.
• Παρόλο ότι έκανε ζέστη, φορούσε ζακέτα. -> Παρόλο που έκανε ζέστη, φορούσε ζακέτα. — παρόλο is completed by που, never by ότι.

Tips

• One-line test for the three patterns: if you could say “maybe it will happen” use pattern 1; if you mean “but it isn’t so” use pattern 2; if you mean “but it wasn’t so” use pattern 3.
• Say the ban out loud until it sticks: μετά το «αν», ποτέ «θα». Learners who internalise this early stop producing the single most recognisable mistake in Greek conditionals.
• Either half may come first. When the αν-clause opens the sentence, a comma separates the two; when it follows, the comma is optional, and standard usage usually keeps it anyway: Θα σου τηλεφωνήσω, αν προλάβω.
• In everyday speech the παρατατικός pattern often does duty for the past as well — Αν το ήξερα, δεν θα ερχόμουν can mean “if I had known, I wouldn’t have come”. The υπερσυντέλικος pattern is the careful, unambiguous version.
• ενώ is doing two jobs: temporal “while” (Ενώ έτρωγα, χτύπησε το τηλέφωνο) and concessive “whereas”. Context, not form, tells them apart.
• The pattern connective + κι αν is productive: όποιος κι αν, όπου κι αν, όποτε κι αν, όσο κι αν all build “no matter who / where / when / how much” from a question word.
• Mind the comma in ό,τι κι αν — ό,τι “whatever” is written with it, while ότι “that” is not.