Το μεγαλύτερο πρόβλημα σήμερα είναι η κίνηση.

Because Greek normally uses the definite article much more regularly than English.

• το μεγαλύτερο πρόβλημα = the biggest problem
• η κίνηση = the traffic

The articles must agree with the noun in gender, number, and case:

• το goes with πρόβλημα, which is neuter singular
• η goes with κίνηση, which is feminine singular

So the articles are not optional here; they are a normal part of the phrase.

Because μεγαλύτερο has to agree with πρόβλημα.

The noun πρόβλημα is:

• neuter
• singular
• nominative

So the adjective must also be neuter singular nominative:

• masculine: μεγαλύτερος
• feminine: μεγαλύτερη
• neuter: μεγαλύτερο

This is a very important Greek pattern: adjectives change form to match the noun they describe.

It can mean either, depending on context.

Formally, μεγαλύτερος / μεγαλύτερη / μεγαλύτερο is the comparative form, meaning bigger or larger. But in Modern Greek, this form is also often used with the definite article to express a superlative meaning:

• το μεγαλύτερο πρόβλημα = the biggest problem

So in this sentence, even though the form is comparative, the meaning is superlative because of the whole phrase and context.

Because that is a very common word order in Greek, just as in English:

• το μεγαλύτερο πρόβλημα = the biggest problem

Greek can sometimes place adjectives after the noun, but that often changes the tone, emphasis, or style. For a straightforward phrase like this, putting the adjective before the noun is the most natural choice.

Είναι is the 3rd person singular of the verb είμαι, meaning to be.

Since the subject is το μεγαλύτερο πρόβλημα (the biggest problem), which is singular, Greek uses the singular verb:

• είμαι = I am
• είσαι = you are
• είναι = he/she/it is

So:

• Το μεγαλύτερο πρόβλημα σήμερα είναι η κίνηση.
• The biggest problem today is traffic.

Σήμερα means today, and Greek allows adverbs like this to move around more freely than English.

In this sentence:

• Το μεγαλύτερο πρόβλημα σήμερα είναι η κίνηση.

the word σήμερα naturally modifies the whole statement: as of today / today, the biggest problem is traffic.

You could also hear:

• Σήμερα το μεγαλύτερο πρόβλημα είναι η κίνηση.

That would also be correct. The difference is mainly one of emphasis and flow, not basic meaning.

Literally, κίνηση means movement. But in everyday Greek, especially in city or commuting contexts, it very often means traffic.

So in this sentence, η κίνηση is understood as:

• traffic on the roads
• traffic congestion

This is a very common real-life use of the word.

There actually is: είναι η κίνηση.

Greek does not need any extra word beyond:

• είναι = is
• η κίνηση = the traffic

So the structure is very direct:

• είναι η κίνηση
• is the traffic

Greek often maps quite neatly onto English in sentences with to be, but the articles and noun endings carry a lot of grammatical information.

Yes. In a sentence with είμαι (to be), both the subject and the thing identified with it are typically in the nominative in Modern Greek.

So here:

• το μεγαλύτερο πρόβλημα = nominative
• η κίνηση = nominative

This is similar to English in the sense that both parts are linked by is rather than one being a direct object.

A rough pronunciation guide is:

To me-ga-LY-te-ro PRO-vli-ma SI-me-ra EE-ne i KEE-ni-si.

A few helpful notes:

• γ before α in μεγαλύτερο sounds like a soft throaty sound, not like English hard g
• η / ι / υ / ει / οι are all pronounced like ee in Modern Greek
• the stress matters:
  • μεγαλύτερο
  • πρόβλημα
  • σήμερα
  • κίνηση

If you ignore the stress marks, your Greek may still be understood, but it will sound much less natural.

Yes. Even though the Greek sentence is structured as:

• The biggest problem today is traffic

English might also naturally say:

• Traffic is the biggest problem today

Both express the same idea. Greek often allows this kind of flexibility too, though changing the order changes the emphasis.

The original Greek puts emphasis first on the biggest problem today, then identifies it as traffic.