Learn Hardcore Turkish: Müsait misiniz, yoksa sizi sonra mı arayayım? - Are you available, or should I call you later?

mi is the question particle (it harmonizes as mi/mı/mu/mü).
-siniz is the 2nd person plural/polite ending. Together they form one word: misiniz. Orthographically, mi is written separate from the word it questions (here: Müsait), but any endings attach to it, so it’s Müsait misiniz? (not “Müsait mi siniz?”).

What’s the difference between misiniz and misin?

misiniz: polite/formal singular or plural “you.”
misin: informal singular “you.” So you’d say Müsait misiniz? to a stranger, superior, or more than one person; Müsait misin? to a friend or someone your own age in an informal context.

Why is mı placed after sonra? Could the question particle go somewhere else?

The question particle attaches to the element being questioned or focused.

Sizi sonra mı arayayım? emphasizes “later (as opposed to now).”
Sizi sonra arayayım mı? is a neutral yes/no question about the whole proposal.
Sizi mi sonra arayayım? emphasizes “you (as opposed to someone else).” All are grammatical; you pick the focus you want.

What does yoksa add compared with veya or ya da?

yoksa means “or else/if not” and introduces an alternative that applies if the first option isn’t true. Here: “Are you available, or else should I call you later?”
veya/ya da are plain “or” and are less natural in this kind of two-part, either–or question. yoksa nicely signals the fallback plan.

Why is it sizi and not size?

Because aramak (“to call”) takes a direct object in the accusative. sizi is the accusative form of siz.
Use size (dative) with verbs like telefon etmek: Size sonra telefon edeyim mi?

Why sizi and not seni?

sizi is the polite/formal or plural object pronoun; seni is the informal singular. The sentence is phrased politely throughout (misiniz, arayayım), so sizi matches that level of formality.

Why arayayım instead of a future tense like arayacağım or arayacak mıyım?

-ayım/-eyim (optative) expresses offering, proposing, or asking for permission: “Shall I/Should I…?”

Arayayım = “Shall I call?” (offer/suggestion)
Arayacağım = “I will call.” (a decision/plan)
Arayacak mıyım? = “Will I call?” (seeking confirmation about the future), which sounds odd here.

Is it arayayım or arayım?

The fully formed optative after a vowel-final stem is -yayım/-yeyim, so ara- → arayayım. In everyday speech (and widely in writing) this commonly contracts to arayım. Both are understood; arayayım is the careful form, arayım is very common and natural.

Can I omit sizi?

Yes. In context, Sonra mı arayayım? still means “Should I call (you) later?” Because the addressee is obvious, Turkish often drops the object pronoun. Including sizi is a bit more explicit/polite.

Why is there a comma before yoksa?

There are two coordinated clauses: “Are you available” and “or else should I call you later.” yoksa introduces the alternative, and a comma neatly separates the two parts. You’ll commonly see that comma in writing.

Are there other polite ways to ask about availability here?

Yes:

Şu an müsait misiniz? (Are you available right now?)
Uygun musunuz? (Are you available/suitable?)
Vaktiniz var mı? (Do you have time?)
Meşgul müsünüz? (Are you busy?) All can be combined with the second clause: … yoksa sizi sonra mı arayayım?

How does vowel harmony affect mi/mı/mu/mü here?

The question particle matches the last vowel of the word it attaches to:

After front unrounded (e, i): mi
After back unrounded (a, ı): mı
After back rounded (o, u): mu
After front rounded (ö, ü): mü So: Müsait misiniz (last vowel of müsait is i → mi), and sonra mı (last vowel a → mı).