Learn Hardcore Russian: Иногда я боюсь темноты, особенно ночью. - Sometimes I am afraid of the dark, especially at night.

The Russian verb бояться always takes its object in the genitive case, not the accusative. So “fear of darkness” is боюсь темноты, not боюсь темноту.

Why is ночью in the instrumental case, and how does it work here?

Many Russian time expressions use the instrumental case to mean “at [time].” The noun ночь (night) in the instrumental becomes ночью, meaning “at night” or “during the night.” It functions as an adverbial modifier of time.

Is the comma before особенно ночью mandatory, and why is it there?

Here особенно ночью is a detached adverbial phrase adding emphasis (“especially at night”). When such clarifying or emphatic modifiers follow the main clause, they are typically set off by a comma to indicate a slight pause and highlight the nuance. The comma is recommended for clarity but in very casual speech it might be dropped.

Where are the word stresses in Иногда я боюсь темноты, особенно ночью?

The stress falls on:

иногда́ (ino-GDÁ)
я (YA)
бою́сь (bo-YUS’)
темно́ты (tem-NÓ-ty)
особенно́ (o-so-BÉN-no)
но́чью ( NÓ-chyu)

Can I drop the pronoun я and still be correct?

Yes. Russian is a pro-drop language, and the verb ending -юсь signals 1st-person singular. You can say Иногда боюсь темноты, особенно ночью, and it remains both correct and natural.

What’s the difference between боюсь темноты and боюсь в темноте?

боюсь темноты (Genitive) expresses a general, almost abstract fear of the concept of darkness.
боюсь в темноте (Prepositional) means “I’m afraid when I am in the dark” — a situational fear experienced in a specific dark environment.

Could I say особенно по ночам instead of особенно ночью, and would it change the meaning?

Yes. по ночам (“by nights”) emphasizes repeated occurrences over multiple nights (habitual sense), whereas особенно ночью highlights night-time in general (a single time-frame). Both are correct with slightly different nuances.

What part of speech is темноты, and how is the noun темнота declined?

темноты is the genitive singular of the feminine noun темнота (“darkness”). It follows the first declension pattern:

Nominative: темнота
Genitive: темноты
Dative: темноте
Accusative: темноту
Instrumental: темнотой
Prepositional: (о) темноте

What kind of word is особенно, and how is it used here?

особенно is an adverb of degree meaning “especially” or “particularly.” It modifies another adverb, adjective, or phrase (here ночью) to intensify or single out that element.