Υποθέτω ότι δεν θα αργήσεις πολύ, γιατί η κίνηση φαίνεται καλύτερη τώρα.

ότι means that and introduces the content of what the speaker is assuming:

Υποθέτω ότι δεν θα αργήσεις πολύ
= I suppose that you won’t be very late

After verbs like υποθέτω, νομίζω, ξέρω, and λέω, Greek often uses ότι or πως to introduce a clause. So Υποθέτω πως... would also be possible.

In Greek, δεν is the normal negation for statements, and it comes before θα:

• θα αργήσεις = you will be late / you will take long
• δεν θα αργήσεις = you won’t be late / you won’t take long

So the order δεν θα is the normal and correct one.

After θα, Greek uses a non-past verb form. Here αργήσεις is the perfective non-past form of αργώ. It does not mean past, even though it may remind learners of forms related to the aorist.

It is used because the speaker is talking about one complete event: your delay or late arrival.

Compare:

• θα αργήσεις = one complete event, so you’ll be late / you’ll take long
• θα αργείς = more ongoing or repeated, like you’ll keep being late or you’ll be arriving late regularly

So θα αργήσεις πολύ is the natural choice here.

αργώ can mean several related things:

• to be late
• to take a long time
• to delay

In this sentence, it could be understood as you won’t be very late or you won’t take much longer. Because the next part talks about traffic, both ideas fit the context well.

πολύ means much / a lot / very much. With αργήσεις, it means by much or for long.

So:

• δεν θα αργήσεις πολύ = you won’t be very late
• or you won’t take much longer

It is modifying the idea of delay.

In Greek, γιατί can mean both why and because. The sentence structure tells you which meaning it has.

Here it introduces a reason, so it means because:

• Γιατί άργησες; = Why were you late?
• Άργησα γιατί είχε κίνηση. = I was late because there was traffic.

Yes. Literally, κίνηση means movement, but in everyday Greek η κίνηση is the normal word for traffic, especially road traffic.

So:

η κίνηση φαίνεται καλύτερη τώρα
= the traffic seems better now

Because καλύτερη has to agree with η κίνηση, which is feminine singular.

The forms are:

• masculine: καλύτερος
• feminine: καλύτερη
• neuter: καλύτερο

So:

• ο δρόμος είναι καλύτερος
• η κίνηση φαίνεται καλύτερη
• το αποτέλεσμα είναι καλύτερο

It is the comparative form of καλός / καλή / καλό = good.

So:

• καλή = good
• καλύτερη = better

Greek often leaves the comparison point unstated if it is obvious from context. So η κίνηση φαίνεται καλύτερη τώρα naturally means the traffic seems better now, with the idea better than before understood.

φαίνεται means seems / appears / looks. It shows that the speaker is judging from appearances or available signs, not stating something as a hard fact.

Compare:

• η κίνηση είναι καλύτερη = the traffic is better
• η κίνηση φαίνεται καλύτερη = the traffic seems / looks better

So φαίνεται makes the sentence a little more cautious and natural.

Greek word order is flexible, and τώρα at the end is completely natural. It gives a slight focus to the time idea: now.

So the sentence flows as:

the traffic seems better now

You could also move it:

• γιατί τώρα η κίνηση φαίνεται καλύτερη

but the original order sounds very natural in everyday Greek.

Yes. αργήσεις is second person singular, so it is used for one person in the informal you form.

If you were speaking politely to one person, or to several people, you would use αργήσετε:

Υποθέτω ότι δεν θα αργήσετε πολύ, γιατί η κίνηση φαίνεται καλύτερη τώρα.