Learn Hardcore Turkish: Fener sönünce çadırı kurmak zorlaştı. - When the flashlight went out, pitching the tent got harder.

It creates a time clause meaning roughly “when/once/after.” It is non-finite and carries no tense by itself; the main verb provides the tense. Here, sön- + -ünce (vowel harmony) = sönünce “when it went out,” and past time comes from zorlaştı.

Could I use söndüğünde or söndükten sonra instead of sönünce?

Yes, with slight nuance differences:

sönünce: when/once it went out (often suggests immediate sequence and can imply causality).
söndüğünde: when it went out/when it is out (more neutral “when”).
söndükten sonra: after it went out (clearer “after,” emphasizes the sequence).

Does sönünce ever imply “because”?

In many contexts, yes. A -ınca/-ince clause can be understood as the reason for the main clause. If you want to be explicitly causal, use … söndüğü için … (“because it went out”).

Why is çadırı in the accusative in çadırı kurmak?

Because the whole phrase çadırı kurmak is a nominalized verb phrase acting as the subject, and the verb’s direct object keeps its normal case-marking inside that phrase. Accusative here also signals definiteness/specificity: “setting up the (specific) tent.” For a non-specific idea, you’d use çadır kurmak or bir çadır kurmak.

Could I say çadır kurmak instead of çadırı kurmak?

Yes, but it changes the meaning:

çadır kurmak: setting up a tent / tent-setting in general (non-specific).
çadırı kurmak: setting up the specific tent (the one in question).

Is çadırı kurmak the subject of zorlaştı?

Exactly. The entire infinitive phrase çadırı kurmak functions as the grammatical subject of zorlaştı (“became difficult”).

What’s the difference between zordu, zor oldu, and zorlaştı?

zordu: it was difficult (state).
zor oldu: it turned out to be difficult / it was difficult on that occasion (event/result).
zorlaştı: it became more difficult (a change from easier to harder).

How is zorlaştı formed morphologically?

zor (adjective “difficult”)
-laş- (inchoative “become X”)
-dı (past) Together: zor-laş-tı = “became difficult.”

Why not use zorlaştırdı here?

zorlaştırmak is transitive: “to make (something) difficult.” Using it requires an explicit subject causing the difficulty:

Fenerin sönmesi çadırı kurmayı zorlaştırdı. (“The lantern’s going out made setting up the tent difficult.”) In the original, zorlaştı is intransitive and more impersonal.

What’s the difference between sönmek and söndürmek?

sönmek: to go out (intransitive; the light dies/goes out by itself).
söndürmek: to put out/turn off (transitive; someone causes it). So fener söndü = “the lantern went out,” while feneri söndürdük = “we turned the lantern off.”

What exactly does fener refer to here?

Context decides. Fener can mean a lantern, flashlight, or even a lighthouse. In a camping context it’s a lantern or flashlight. More specific terms:

el feneri: flashlight/torch
kamp feneri: camp lantern
deniz feneri: lighthouse

Can I reverse the clause order or add a comma?

Yes:

Fener sönünce, çadırı kurmak zorlaştı. (comma is common but optional)
Çadırı kurmak zorlaştı, fener sönünce. (main clause first is also fine, slightly more afterthought-like)

How can I say who had difficulty doing it?

Use a -mA nominalization with a possessor:

Benim çadırı kurmam zorlaştı.
Bizim çadırı kurmamız zorlaştı. Or keep -mak and add a “for” phrase:
Bizim için çadırı kurmak zorlaştı.

Could I use -ken instead of -ince (e.g., sönerken)?

-ken means “while/as (something is happening).” Fener sönerken… = “while the lantern was going out…,” which focuses on the ongoing process. -ince marks the point/event of completion: “when it went out.”

Where does the past sense on the sönünce clause come from?

From the main verb’s past -dı in zorlaştı. The -ınca/-ince clause itself is tenseless and takes its time reference from the main clause.

Any close paraphrases within Turkish that keep the same idea?

Fener söndüğünde çadırı kurmak zorlaştı.
Fener söndükten sonra çadırı kurmak zorlaştı.
More explicit cause-effect: Fener söndüğü için çadırı kurmak zorlaştı.