Learn Hardcore Turkish: O aniden ağlamaya başladı, ben onu sakinleştirip su verdim. - She suddenly started crying; I calmed her down and gave her water.

With verbs, başlamak takes the verbal noun in the dative: -mA(y)a. So the correct pattern is: verb stem + -mA + -(y)a → ağla-mA-ya başladı.

ağlamayı başladı is wrong with başlamak.
ağlama başladı is grammatical but different: it means “the crying started” (treating ağlama as a noun), not “he/she started to cry.”

What does the -ip in "sakinleştirip" do?

The suffix -ip is a converb that links two actions with the same subject and tense: “X and (then) Y.” So sakinleştirip su verdim = “I calmed [him/her] down and (then) gave [some] water.” You could also say “sakinleştirdim ve su verdim,” but -ip is more compact and suggests sequence.

Why is it "onu" (accusative) before "sakinleştirip," not "ona" (dative)?

Because sakinleştirmek (“to calm someone down”) is a transitive verb that takes a direct object in the accusative: onu. The dative ona would be used with verbs that take an indirect object (e.g., yardım etmek “to help [someone]”).

Should it be "ona su verdim" instead of just "su verdim"?

If you want to specify the recipient, yes: ona su verdim (“I gave water to him/her”). The sentence as written is natural in conversation (the recipient is recoverable from context), but the most explicit version is: Onu sakinleştirip ona su verdim.

Why doesn’t "su" take the accusative (-ı) here?

In Turkish, the direct object takes accusative only if it’s definite/specific. su verdim = “I gave (some) water” (indefinite). If you mean “the water,” use suyu verdim.

Can I drop the subject pronouns “O” and “ben”?

Yes. Verb endings already show person: başladı (3rd sing.), verdim (1st sing.). You could say: Aniden ağlamaya başladı, onu sakinleştirip (ona) su verdim. Keeping O and ben is fine for clarity and to highlight the subject switch.

Would adding "de" in "ben de" be more natural?

Often, yes. ben de (“I too/so I”) neatly shows your responsive action: O aniden ağlamaya başladı; ben de onu sakinleştirip ona su verdim.

Is the comma between the clauses okay?

Colloquially, yes. In careful writing, prefer a semicolon or add a connector:

O aniden ağlamaya başladı; ben de onu sakinleştirip ona su verdim.
O aniden ağlamaya başladı ve ben de onu sakinleştirip ona su verdim.

Where can "aniden" go, and are there alternatives?

Typical placements: O aniden ağlamaya başladı or Aniden ağlamaya başladı. Alternatives: birden (very common), birdenbire (more emphatic), bir anda (“all of a sudden”). aniden can feel a bit more formal.

What does "o" mean here—he, she, or it?

Turkish o is gender-neutral and can mean “he,” “she,” or “it.” Context decides. There’s no grammatical gender.

What’s the difference between "sakinleştirmek" and "sakinleşmek"?

sakinleşmek: to calm down (intransitive; the subject calms themselves).
sakinleştirmek: to calm someone/something down (causative, transitive; takes an object: onu).
Morphology: sakin → sakin-leş- (become calm) → sakin-leş-tir- (cause to become calm).

Why is there a "y" in "ağlamaya"?

It’s the buffer consonant -y- used to prevent vowel clash between ağlama (ağla-mA) and the dative -a: ağlama + a → ağlamaya.

Could I use "-erek" or "-dikten sonra" instead of "-ip"?

Yes, but the nuance changes:

Onu sakinleştirip su verdim: did X and then Y (simple sequence).
Onu sakinleştirerek su verdim: “I gave water by calming him/her (as/while calming).”
Onu sakinleştirdikten sonra su verdim: explicitly “after calming him/her, I gave water.”
For a quick chronological chain, -ip is the most neutral.

Any quick pronunciation tips for “ağlamaya başladı” and “sakinleştirip”?

ğ: lengthens the preceding vowel; it’s not a hard “g.” So ağ is like a long “aa.”
ı (dotless i): like a relaxed “uh” sound.
ş = “sh,” ç = “ch.”
So: a(a)h-la-ma-ya ba-shla-dı; sa-kin-leş-ti-rip.