Learn Hardcore Greek: Σήμερα είμαι χαρούμενος, αλλά χτες ήμουν λυπημένος. - Today I am happy male, but yesterday I was sad male.

Present:
- είμαι – I am
- είσαι – you are
- είναι – he/she/it is, they are
- είμαστε – we are
- είστε – you are (plural/polite)
Past:
- ήμουν – I was
- ήσουν – you were
- ήταν / ήτανε – he/she/it was, they were
- ήμασταν – we were
- ήσασταν – you were (plural/polite)

In the sentence:

είμαι χαρούμενος = I am happy (now, today)
ήμουν λυπημένος = I was sad (before, yesterday)

What is the difference between σήμερα and χτες?

Both are time adverbs:

σήμερα = today
χτες (or χθες) = yesterday

They work just like English today and yesterday and usually go at the beginning or end of the sentence:

Σήμερα είμαι χαρούμενος. – Today I am happy.
Είμαι χαρούμενος σήμερα. – I am happy today.
Χτες ήμουν λυπημένος. – Yesterday I was sad.
Ήμουν λυπημένος χτες. – I was sad yesterday.

I see χτες in some places and χθες or εχθές in others. What is the difference?

They all mean the same thing: yesterday.

χτες – very common, more informal spelling
χθες – slightly more “formal”/traditional spelling
εχτές / εχθές – also correct, but used a bit less in everyday writing

In everyday modern Greek, χτες is very frequent in speech and informal writing, and χθες is common in more formal or careful writing. All are understood everywhere.

Why is σήμερα at the beginning of the sentence? Could it go somewhere else?

Time words like σήμερα (today) and χτες (yesterday) are flexible.

All of these are correct:

Σήμερα είμαι χαρούμενος.
Είμαι σήμερα χαρούμενος.
Είμαι χαρούμενος σήμερα.

Putting σήμερα first slightly emphasizes today as a contrast to yesterday in the second part of the sentence:

Σήμερα είμαι χαρούμενος, αλλά χτες ήμουν λυπημένος.

This today vs yesterday contrast is very natural at the start of each clause.

Why is there a comma before αλλά? Is it required?

αλλά means but. In Greek, when αλλά connects two full clauses (each with its own verb), a comma before it is normal and recommended, just like in English:

Σήμερα είμαι χαρούμενος, αλλά χτες ήμουν λυπημένος.

If αλλά only connects two words or short phrases (not full clauses), you normally do not put a comma:

Είμαι χαρούμενος αλλά κουρασμένος. – I am happy but tired.

Why is it χαρούμενος and λυπημένος and not some other endings?

χαρούμενος and λυπημένος are masculine singular adjective forms. In Greek, adjectives change their ending to agree with the noun (or the implied subject) in gender and number.

Basic pattern for many adjectives:

Masculine: -ος (e.g. χαρούμενος, λυπημένος)
Feminine: -η (e.g. χαρούμενη, λυπημένη)
Neuter: -ο (e.g. χαρούμενο, λυπημένο)

So:

A man would say: Είμαι χαρούμενος.
A woman would say: Είμαι χαρούμενη.
Talking about a neuter noun: Το παιδί είναι χαρούμενο. – The child is happy.

If I am a woman, how would I change the sentence?

You only change the adjectives to the feminine forms:

Σήμερα είμαι χαρούμενη, αλλά χτες ήμουν λυπημένη.

Everything else (σήμερα, είμαι, αλλά, χτες, ήμουν) stays the same. The verb does not change with gender; only the adjectives do.

What is the difference between σήμερα and τώρα?

σήμερα = today (the whole day)
τώρα = now (this moment)

So:

Σήμερα είμαι χαρούμενος. – I am happy today (all through today / as a general state today).
Τώρα είμαι χαρούμενος. – I am happy now (at this moment; maybe I wasn’t before).

You can also combine them:

Τώρα, σήμερα είμαι χαρούμενος. – Now, today I am happy. (Strong focus and contrast.)

Could I drop the verb ήμουν in the second part and just say χτες λυπημένος?

In careful standard Greek, you usually keep ήμουν:

Σήμερα είμαι χαρούμενος, αλλά χτες ήμουν λυπημένος.

In informal speech, Greeks often omit the second είμαι/ήμουν if it is very clear from context, or they repeat the first verb in their mind:

Σήμερα είμαι χαρούμενος, αλλά χτες λυπημένος.

This is understood as …αλλά χτες (ήμουν) λυπημένος.

For learners, it is safer and clearer to keep the verb in both parts until you feel comfortable with ellipsis in Greek.

Where do the stress accents go in these words, and how do they affect pronunciation?

Modern Greek uses one written accent per word, showing which syllable is stressed. In this sentence:

Σήμερα – ΣΉ-με-ρα (stress on ΣΗ)
είμαι – ΕΊ-μαι (stress on ΕΙ)
χαρούμενος – χα-ΡΟΎ-με-νος (stress on ΡΟΥ)
χτες – one syllable, stress on the only syllable
ήμουν – Ή-μουν (stress on Η)
λυπημένος – λυ-πη-ΜΈ-νος (stress on ΜΕ)

Stress is important in Greek: changing the stress can make the word sound wrong or even turn it into a different word. Always pronounce the stressed syllable a bit louder/longer.

What does αλλά mean exactly, and is it the only word for but?

αλλά means but, used to contrast two statements:

Είμαι χαρούμενος, αλλά είμαι κουρασμένος. – I am happy, but I am tired.

Other contrast words exist (for example όμως = however), but αλλά is the main simple word for but and is the most common one to learn and use first.

Could I say έχω χαρά instead of είμαι χαρούμενος?

You can say έχω χαρά (literally I have joy), but:

είμαι χαρούμενος = I am happy (normal, very common way to talk about your emotional state)
έχω χαρά = I have joy / I feel joy (sounds a bit more like you are experiencing joy because of something specific – can be slightly more literary or context-dependent)

For everyday I am happy / I was sad, the most natural Greek is:

είμαι χαρούμενος / λυπημένος
ήμουν χαρούμενος / λυπημένος

What is the origin/nuance of λυπημένος?

λυπημένος is the past participle/adjectival form of the verb λυπάμαι (I am sad / I feel sorry).

λυπάμαι – I am sad / I feel sorry
λυπημένος – sad (in a state of sadness)

So είμαι λυπημένος literally means I am (in a sad state). In everyday English we just say I am sad, so λυπημένος is best translated as sad.