Πριν έρθουν οι καλεσμένοι, ισιώνω το πατάκι στην είσοδο.

Because after πριν (before), Greek often uses the subjunctive form to refer to an action that has not happened yet.

So:

• πριν έρθουν οι καλεσμένοι = before the guests arrive / before the guests come

The form έρθουν is the aorist subjunctive of έρχομαι. It is used because the arrival is seen as a single completed event.

Why not the others?

• έρχονται = they are coming / they come
  This is indicative, not the usual choice here.
• θα έρθουν = they will come
  Greek normally does not use θα after πριν in this kind of clause.

It comes from έρχομαι (to come), but this verb is irregular.

Some important forms are:

• έρχομαι = I come / I am coming
• ήρθα = I came
• να έρθω = that I come / to come
• να έρθουν = that they come

So έρθουν is the 3rd person plural form: they come / they arrive in a subjunctive environment.

This is very common in Greek: some verbs use a different stem in the aorist.

That is a very common question. In Modern Greek, πριν can be followed by a subjunctive clause, and να is often omitted.

So both of these are possible:

• Πριν έρθουν οι καλεσμένοι
• Πριν να έρθουν οι καλεσμένοι

In many contexts, the version without να sounds very natural and common.

So yes, έρθουν is still a subjunctive-type form, even though να is not written here.

Greek often uses the present tense for:

• habitual actions
• general routines
• sometimes a vivid present

Here, the sense is probably something like:

• Before the guests arrive, I straighten the doormat at the entrance.

That sounds like a usual thing I do whenever guests are about to come.

So ισιώνω does not have to mean only right now at this moment. It can also mean this is what I do.

If you wanted a one-time past event, you would use a past tense instead.

ισιώνω means to straighten, to make even, to smooth out, or to put straight.

With το πατάκι, it suggests something like:

• straightening the mat
• adjusting it so it lies properly
• making it neat

So it is not just cleaning the mat. It is more specifically putting it straight/in order.

πατάκι usually means a small mat or doormat.

In this sentence:

• το πατάκι στην είσοδο = the doormat / small mat at the entrance

It comes from πατάω (to step on) historically, so a πατάκι is basically something you step on.

Depending on context, it can mean:

• doormat
• bath mat
• small floor mat

Here, because of στην είσοδο, doormat is the most natural translation.

Because σε + την contracts to στην.

So:

• σε την είσοδο → στην είσοδο

This is completely standard.

Similar contractions:

• σε το → στο
• σε τον → στον
• σε τους → στους
• σε τις → στις

So στην είσοδο simply means at / in the entrance.

Both main noun phrases here are in the nominative or accusative, depending on their role:

• οι καλεσμένοι = the guests → nominative plural
  They are the subject of έρθουν.
• το πατάκι = the mat / doormat → accusative singular
  It is the object of ισιώνω.
• στην είσοδο = at the entrance
  After σε, Greek uses the accusative, so είσοδο is accusative singular.

So the structure is:

• subordinate clause: οι καλεσμένοι = subject
• main clause: implied I = subject, το πατάκι = object
• στην είσοδο = prepositional phrase of location

Greek often omits subject pronouns when they are already clear from the verb ending.

Here:

• ισιώνω = I straighten

So Greek does not need εγώ unless you want emphasis.

Compare:

• Ισιώνω το πατάκι. = I straighten the mat.
• Εγώ ισιώνω το πατάκι. = I straighten the mat.
  This sounds more emphatic, like contrasting with someone else.

This is very normal in Greek.

Greek word order is more flexible than English.

Both the verb-first and subject-first patterns can appear, but:

• Πριν έρθουν οι καλεσμένοι sounds natural and smooth
• it places focus on the event arrive
• then names who is arriving: the guests

Greek often puts the verb before the subject, especially in subordinate clauses or when presenting an event.

So this word order is normal and idiomatic.

Literally, καλεσμένοι means invited ones / invited people, from the verb καλώ (to invite / call).

But in everyday Greek, οι καλεσμένοι very naturally means:

• the guests

So the literal and natural meanings overlap here. In this sentence, it does not sound overly formal or strange; it is a common way to say guests.

Not with this verb clause in the same way.

• πριν is used before a clause:
  Πριν έρθουν οι καλεσμένοι
• πριν από is usually used before a noun phrase or time expression:
  πριν από μία ώρα = an hour ago / before an hour

So in this sentence, πριν is the correct choice because it introduces a whole clause: the guests arrive.

Most naturally, it sounds habitual:

• Before the guests arrive, I straighten the doormat at the entrance.

That is because the main verb ισιώνω is in the present tense, which often suggests a routine or repeated action.

However, depending on context, Greek present can sometimes be used more vividly, so a speaker could also use it in a more immediate sense. Still, without more context, a learner should understand it mainly as a usual action.