Learn Farsi: اصلاح کردن تکیه‌گاه صندلی باعث شد که او راحت بنشیند. - Correcting the chair's backrest caused him to sit comfortably.

With the structure باعث شدن که (to cause to), the resulting action is viewed as a potential outcome or intent rather than an independent completed fact. Because of this, it almost always takes the present subjunctive (here, بنشیند), regardless of the tense of the main verb.

How does the phrase اصلاح کردن تکیه‌گاه صندلی function as the subject here, and how are the words linked?

In Farsi, full infinitives (ending in -ن) can act as nouns, much like English "-ing" gerunds. Here, اصلاح کردن (correcting/adjusting) is the entire subject. It links to its direct object تکیه‌گاه (backrest) using the ezafe vowel (pronounced e), which then links to صندلی (chair) with another ezafe.

I usually see اصلاح کردن translated as "shaving" or "getting a haircut". How does it mean "correcting" here?

While it is very commonly used for grooming in everyday speech, the core literal meaning of اصلاح کردن is "to correct", "to reform", or "to adjust". In this context, it simply means making a correction or adjustment to the chair.

The English translation says "comfortably", but راحت means "comfortable". Why isn't there an adverbial suffix?

Unlike English, which often adds "-ly" to turn adjectives into adverbs, Farsi frequently uses the exact same word for both. راحت modifies the verb directly here, so it naturally translates as the adverb "comfortably" without needing any extra suffix.