Learn Hardcore Turkish: Kurala göre telefonlar sessizde olmalı, yoksa dışarıda konuşun. - According to the rule, phones must be on silent; otherwise talk outside.

göre is a postposition meaning "according to / in line with / compared to" and it requires the dative case on the preceding noun. So kural-a göre is literally "according to the rule." The -a/-e ending is the dative case marker chosen by vowel harmony (here, a because the last vowel in kural is a back vowel, a).

Does Kurala göre mean "according to a rule" or "according to the rule(s)"? Could I say Kurallara göre?

Kurala göre usually implies a specific rule that is understood from context (like a house rule or posted policy). Turkish doesn’t use articles, so "the" is inferred pragmatically.
Kurallara göre means "according to the rules" (plural), and is very common on signs.
A very idiomatic alternative is Kural gereği / Kurallar gereği ("as required by the rule(s)"). All are acceptable; choose singular vs. plural depending on whether you’re invoking one rule or the set of rules.

Why is telefonlar plural? Could I use the singular telefon or the possessive telefonlarınız?

Turkish often uses a bare plural for general instructions: Telefonlar … = "Phones …" in the generic sense (all phones).
Singular generic (Telefon …) is possible but sounds less natural on signage.
Telefonlarınız ("your phones") is also common on polite notices because it addresses the audience directly. It feels more personal/polite but slightly longer.

What exactly does sessizde mean? Why the ending -de?

sessizde = sessiz (silent) + -de (locative "in/at/on"): "in silent (mode)" → "on silent."
The locative is used for states or modes: you are "in" a state. Compare: Uçak modunda ("in airplane mode").
This is idiomatic in modern Turkish for devices: Telefonunuz sessizde mi? = "Is your phone on silent?"

Why not sessizce? What’s the difference between sessizde and sessizce?

sessizde (locative) describes a state/mode: "on silent."
sessizce is an adverb meaning "quietly" and modifies how an action is done (e.g., sessizce konuşmak = "to speak quietly"). It would not express putting a phone on silent.

Is Telefonlar sessizde olmalı the most idiomatic way? How about sessize alınmalı?

Both are fine:

Telefonlar sessizde olmalı = "Phones should be on silent (state)."
Telefonlar sessize alınmalı = "Phones should be put on silent (be set to silent)." This sounds a bit more precise and is very common in notices. You’ll also see the passive: Telefonlar sessize alınmış olmalı ("should have been set to silent").

What does the ending -malı/-meli in olmalı express? How strong is it compared to other ways of saying "must/should"?

-malı/-meli is the necessitative mood, usually "should/ought to" and can range up to "must" depending on context/tone. Rough strength (context-sensitive):

Softer: … olmalı ~ should/ought to
Neutral necessity: … gerek / gerekiyor ~ need to / have to
Strong obligation: … zorunda (olmak) ~ must
Formal/authoritative: … olmalıdır (adds assertive -dır)

What does yoksa do here? Is it the same as "otherwise"?

Yes. yoksa is "otherwise / or else" connecting two clauses: "Phones should be on silent; otherwise, talk outside." Historically it’s a contraction of yok ise ("if [that is] not the case"). It also appears in questions meaning "or…?": Yoksa gelmiyor musun? ("Or are you not coming?")

Why is there a comma before yoksa?

You’re linking two independent clauses with a conjunction ("otherwise"). A comma is standard and improves readability: main clause, then consequence with yoksa.

Why dışarıda and not dışarı?

dışarıda = locative "outside (at the outside area)" → "speak outside (there)."
dışarı (without -da) often has directional sense "outside/out" and is used with motion verbs: dışarı çık ("go outside"). So for "speak outside," use dışarıda konuşun. For "go outside and speak," you could say Dışarı çıkıp konuşun.

What does konuşun tell me about person/politeness? How would it change with different audiences?

konuşun is the 2nd person plural imperative. It addresses:
- a group (you all), or
- a single person politely (the "siz" form).
Variants:
- konuş (singular informal)
- konuşunuz (very formal/polite, often on official signs) Adding lütfen softens the tone: Lütfen dışarıda konuşun(uz).

Could the sentence use the negative imperative, like "don’t talk here; talk outside"?

Yes. A common, slightly clearer version is:

Burada konuşmayın; konuşacaksanız dışarıda konuşun. Or shorter:
Burada konuşmayın, lütfen dışarıda konuşun. Your original uses yoksa to express the alternative action instead of a local prohibition.

Are there word-order alternatives that still sound natural?

Yes. Turkish is flexible with adjuncts:

Telefonlar kurala göre sessizde olmalı, yoksa dışarıda konuşun.
Kurallara göre telefonlar sessize alınmalı, yoksa dışarıda konuşun. Placing kurala/kurallara göre at the start is common because it sets the rule-based frame.

Why is it sessiz-de (with -de) and not sessiz-te? And why -de vs -da?

Two phonological rules:

Voicing: The locative uses -d- after a vowel or voiced consonant, and -t- after a voiceless consonant. sessiz ends in z (voiced) → -de.
Vowel harmony: Front vowels (e, i, ö, ü) take -de; back vowels (a, ı, o, u) take -da. sessiz has front vowels (e, i) → -de. That’s why sessizde, and likewise dışarıda (back vowel a/ı → -da).

Can you break down the forms in the sentence?

Kurala = kural (rule) + -a (dative, "to") → "to the rule"
göre = postposition "according to"
telefonlar = telefon (phone) + -lar (plural)
sessizde = sessiz (silent) + -de (locative, "in/at") → "on silent (mode)"
olmalı = ol- (be) + -malı (necessitative, "should/must")
yoksa = "otherwise / or else" (from yok ise)
dışarıda = dışarı (outside) + -da (locative, "outside/at the outside")
konuşun = konuş- (speak) + -un (2nd person plural/polite imperative)