Ένα μικρό χαμόγελο και λίγη ευγένεια αλλάζουν αμέσως την ατμόσφαιρα.

Ένα is the neuter singular form of the indefinite article ένας / μία(μια) / ένα, meaning a / an or sometimes one.

Because χαμόγελο is a neuter noun, Greek uses ένα χαμόγελο.

• ένας = masculine
• μία / μια = feminine
• ένα = neuter

So ένα μικρό χαμόγελο is grammatically matched all the way through: article + adjective + noun are all neuter singular.

Greek adjectives must agree with the noun they describe in gender, number, and case.

Here, χαμόγελο is:

• neuter
• singular
• nominative (because it is part of the subject)

So the adjective also has to be neuter singular nominative: μικρό.

That is why you get:

• ένα μικρό χαμόγελο

and not μικρή or μικρός.

Because ευγένεια here is being treated as an abstract / uncountable idea, like politeness in English.

So λίγη ευγένεια means a little politeness, which sounds natural.

Using μια ευγένεια would sound much less natural in this context, because it suggests one politeness or a politeness, which is not how this idea is normally expressed.

Also, λίγη agrees with ευγένεια, which is:

• feminine
• singular

So:

• λίγος = masculine
• λίγη = feminine
• λίγο = neuter

Because the subject is actually two things joined by και:

• ένα μικρό χαμόγελο
• λίγη ευγένεια

Together, they form a compound subject, so Greek uses a plural verb.

That is why the sentence has:

• αλλάζουν = they change

Even though each item by itself is singular, the two together are plural in meaning: a small smile and a little politeness change...

No. They just look similar.

• αλλά = but
• αλλάζουν = they change

Αλλάζουν comes from the verb αλλάζω, meaning to change.

So in this sentence, αλλάζουν is the verb, not the conjunction but.

Αλλάζουν is the 3rd person plural present active form of αλλάζω.

So it means:

• they change
• are changing

In this sentence, the subject is the two-part phrase ένα μικρό χαμόγελο και λίγη ευγένεια, so the verb correctly appears in 3rd person plural.

A few related forms:

• αλλάζω = I change
• αλλάζεις = you change
• αλλάζει = he/she/it changes
• αλλάζουμε = we change
• αλλάζετε = you (plural) change
• αλλάζουν = they change

Because ατμόσφαιρα is the direct object of the verb αλλάζουν.

The sentence is asking: what do they change?
Answer: the atmosphere.

So Greek uses the accusative case:

• nominative: η ατμόσφαιρα
• accusative: την ατμόσφαιρα

The article changes to την, while the noun here stays the same in form.

Also, the final -ν in την is kept because the next word begins with a vowel: ατμόσφαιρα.

The sentence has two main case roles:

1. Subject (nominative)

• ένα μικρό χαμόγελο
• λίγη ευγένεια

These are the things doing the action, so they are in the nominative.

2. Direct object (accusative)

• την ατμόσφαιρα

This is the thing being changed, so it is in the accusative.

For English speakers, this is useful because Greek shows these relationships more clearly through articles and endings than English does.

Αμέσως means immediately, right away, or at once.

It is an adverb, modifying the verb αλλάζουν.

Its position here is very natural:

• αλλάζουν αμέσως την ατμόσφαιρα

Greek word order is fairly flexible, so you may also see αμέσως in other positions, depending on emphasis. But in this sentence, its placement is neutral and natural.

Yes. Greek word order is more flexible than English word order, because Greek relies more on case forms and verb endings.

The given order is a very natural, neutral one:

• Ένα μικρό χαμόγελο και λίγη ευγένεια αλλάζουν αμέσως την ατμόσφαιρα.

But other orders are possible for emphasis, for example putting αμέσως earlier.

Still, for a learner, the original version is a good model because it is clear and standard: subject + verb + adverb + object.

Because λίγη already works as the determiner here.

In λίγη ευγένεια, the idea is a little politeness, not the politeness. So Greek does not need an extra article before ευγένεια.

Compare the roles:

• η ευγένεια = the politeness
• λίγη ευγένεια = a little politeness

So the phrase is already complete and natural without η.