Όταν το μάθημα είναι ευχάριστο, ο χρόνος περνάει γρήγορα.

When the lesson is pleasant, time passes quickly.

Breakdown of Όταν το μάθημα είναι ευχάριστο, ο χρόνος περνάει γρήγορα.

• είμαι: to be
• όταν: when
• ο χρόνος: the time
• γρήγορα: quickly
• το μάθημα: the lesson
• περνάω: to pass
• ευχάριστος: pleasant

Questions & Answers about Όταν το μάθημα είναι ευχάριστο, ο χρόνος περνάει γρήγορα.

What does Όταν mean here, and how is it different from αν?

Όταν means when in the sense of whenever / every time that.
In this sentence it introduces a general condition that is regularly true:

• Όταν το μάθημα είναι ευχάριστο… = When(ever) the lesson is pleasant…

Όταν is used with time clauses.
Αν means if and is used for conditions that may or may not happen:

• Αν το μάθημα είναι ευχάριστο… = If the lesson is pleasant… (maybe it is, maybe it isn’t)

So:

• όταν → time, whenever/when
• αν → condition, if

Why is it το μάθημα and not something like ένα μάθημα for a lesson?

Greek uses the definite article (ο, η, το) much more than English, even for general statements.

• Το μάθημα literally is the lesson, but in a general, generic way.
• In English we would usually say when a lesson is pleasant or when the lesson is pleasant, but in Greek the natural way is with the definite article: το μάθημα.

Using ένα μάθημα would sound like you are talking about one specific, single lesson out of others, not about lessons in general.

Why is it το μάθημα but ο χρόνος? What do το and ο mean?

Το and ο are both definite articles (the), but they mark different genders:

• ο χρόνος = the time (masculine, singular, nominative)
• το μάθημα = the lesson (neuter, singular, nominative)

In Greek every noun has grammatical gender:

• masculine: ο (ο χρόνος, ο φίλος)
• feminine: η (η ώρα, η μέρα)
• neuter: το (το μάθημα, το βιβλίο)

Here both μάθημα and χρόνος are subjects, so they are in the nominative case with their matching article.

What is είναι, and why do we need it?

Είναι is the 3rd person singular form of the verb είμαι (to be):
είναι = he is / she is / it is / they are, depending on context.

In this sentence:

• το μάθημα είναι ευχάριστο = the lesson is pleasant

Greek, like English, must include the verb to be in such sentences; you cannot drop it.

Why does ευχάριστο end in -ο and not -ος?

The basic adjective is ευχάριστος, -η, -ο = pleasant, enjoyable.

Adjectives must agree with the noun in:

• gender
• number
• case

Since μάθημα is neuter singular, nominative:

• neuter singular nominative of the adjective is ευχάριστο

So we get:

• το ευχάριστο μάθημα
• το μάθημα είναι ευχάριστο

If the noun were masculine (ο καθηγητής = the teacher), it would be:

• ο καθηγητής είναι ευχάριστος.

What exactly does περνάει mean, and which verb is it from?

Περνάει is 3rd person singular present of the verb περνάω / περνώ, which means:

• to pass (by), to go by, to spend (time)

Here it means time passes / goes by:

• ο χρόνος περνάει = time passes / time goes by

In everyday Greek, you will also hear the shorter form περνά:

• ο χρόνος περνά γρήγορα (equally correct in speech).

Why is it ο χρόνος with the article, instead of just χρόνος?

Abstract nouns like time, love, life usually take the definite article in Greek when used in a general sense:

• ο χρόνος περνάει γρήγορα = time passes quickly
• η ζωή είναι δύσκολη = life is hard
• η αγάπη είναι σημαντική = love is important

Leaving out the article here (χρόνος περνάει γρήγορα) would sound unnatural or incomplete in standard modern Greek.

What is γρήγορα exactly? Why not γρήγορος?

Γρήγορος is the adjective: fast, quick (describes a noun):

• ένα γρήγορο αυτοκίνητο = a fast car

Γρήγορα is the adverb: quickly, fast (describes how something is done):

• ο χρόνος περνάει γρήγορα = time passes quickly

So:

• adjective: γρήγορος / γρήγορη / γρήγορο (for nouns)
• adverb: γρήγορα (for verbs like περνάει).

Can I change the word order? For example, say Ο χρόνος περνάει γρήγορα όταν το μάθημα είναι ευχάριστο?

Yes, that word order is perfectly correct:

• Όταν το μάθημα είναι ευχάριστο, ο χρόνος περνάει γρήγορα.
• Ο χρόνος περνάει γρήγορα όταν το μάθημα είναι ευχάριστο.

Both mean the same thing.
Greek word order is quite flexible; moving the όταν-clause to the end is mostly a matter of emphasis and style, not grammar.

Why are both verbs in the present tense in Greek, even though English might also say goes by or talk about a general truth?

Here, Greek and English actually match closely: both use the present simple to express a general truth/habitual situation:

• Όταν το μάθημα είναι ευχάριστο, ο χρόνος περνάει γρήγορα.
• When the lesson is pleasant, time passes/goes by quickly.

In Greek:

• for general truths and repeated situations, the present tense is standard in both the όταν-clause and the main clause.
• for a specific future event, you’d use όταν with the subjunctive or future and possibly θα in the main clause, e.g.
  Όταν τελειώσει το μάθημα, ο χρόνος θα έχει περάσει γρήγορα. = When the lesson finishes, time will have passed quickly.

How do you pronounce the whole sentence?

Approximate pronunciation (stress in CAPITALS / accented syllables):

Όταν το μάθημα είναι ευχάριστο, ο χρόνος περνάει γρήγορα.
→ Ó-tan to MÁ-thi-ma Í-ne ef-HÁ-ri-sto, o HRÓ-nos per-NÁ-i GRÍ-go-ra.

Notes:

• η and ει are pronounced like i (as in machine).
• χ in χρόνος is like the ch in German Bach or Spanish j in José.
• αι in περνάει sounds like e in pet.