Learn Hardcore Turkish: Öğretmen sizi uyardı.

Because uyarmak (to warn) takes a direct object for the person being warned: you warn someone. So the person is in the accusative: sizi. The dative size would be used with verbs like söylemek (to tell) or vermek (to give).

How is the verb uyardı formed?

It’s the stem uyar- (warn) + past tense -dı with 3rd person singular (zero ending): “(he/she) warned.” Other persons: uyardım, uyardın, uyardı, uyardık, uyardınız, uyardılar. The -dı vowel follows vowel harmony.

Why isn’t there “the” before öğretmen? How do I say “a teacher”?

Turkish has no articles like “the/a.” Bare öğretmen can mean “the teacher” when context makes it definite. To make it clearly indefinite, use bir: Bir öğretmen sizi uyardı = “A teacher warned you.”

Can I change the word order? Does it change the meaning?

Yes, Turkish word order is flexible and affects emphasis (focus is right before the verb).

Neutral: Öğretmen sizi uyardı.
Emphasize “you”: Sizi öğretmen uyardı.
Emphasize “teacher”: Öğretmen sizi uyardı or Öğretmen sizi uyardı (context-dependent), or use Öğretmen mi sizi uyardı? in a question.

How would I say it to one person informally?

Use the singular informal object pronoun: Öğretmen seni uyardı (“The teacher warned you (singular, informal)”).

Can I drop the object pronoun and still mean “warned you”?

No. Turkish verbs don’t agree with the object, so you need seni/sizi to say “you.” Öğretmen uyardı means “The teacher warned (someone),” with the object left unspecified.

What about the plural subject “teachers”?

Use öğretmenler. The verb can be either singular or take a plural marker:

Öğretmenler sizi uyardı.
Öğretmenler sizi uyardılar. Both are correct; the -lar on the verb is optional, but common with human plural subjects.

Why not öğretmeni instead of öğretmen?

Öğretmeni is either accusative “the teacher” as an object or “his/her teacher” (possessed). Öğretmeni uyardı = “He/she warned the teacher” or “He/she warned his/her teacher,” not a subject. For a subject, use bare öğretmen.

How do I negate it or turn it into a question?

Negative: Öğretmen sizi uyarmadı (“didn’t warn you”).
Yes/no question: Öğretmen sizi uyardı mı?
Focused question: Sizi mi uyardı? (“Was it you that he warned?”) / Öğretmen mi uyardı? (“Was it the teacher who warned you?”)

What’s the difference between uyardı and uyarmış?

Uyardı is the plain past (speaker has direct knowledge). Uyarmış is the evidential past (hearsay/inference): “apparently/it seems (he) warned.”

How do I add what you were warned about?

Use a noun + hakkında/konusunda or similar:

Öğretmen sizi tehlike konusunda uyardı (“warned you about the danger”).
With a clause: Öğretmen sizi dışarı çıkmamanız konusunda uyardı (“warned you about not going out”).

Pronunciation tips for this sentence?

ö in öğretmen: like German ö/French eu.
ğ: lengthens the preceding vowel; it isn’t a hard g. öğ ≈ a long “ö.”
ı in uyardı: dotless ı, a back unrounded vowel [ɯ], like the “uh” in “sofa,” but tighter.
Stress typically falls near the end: uyardı, öğretmen.

Are there common synonyms for uyarmak?

Yes: ikaz etmek (“to warn”) and the set phrase uyarıda bulunmak (“to issue a warning”). Example: Öğretmen sizi ikaz etti.

Does sizi necessarily mean plural here, or could it be polite singular?

It’s ambiguous between plural “you all” and polite singular “you.” Only context clarifies which one is meant.