Сегодня я читаю дольше, чем вчера.

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Breakdown of Сегодня я читаю дольше, чем вчера.

• читать: to read
• вчера: yesterday
• сегодня: today

Questions & Answers about Сегодня я читаю дольше, чем вчера.

What exactly is дольше, and what is the base word?

дольше is the comparative form of the adverb долго (“for a long time”). It means “longer (in time)” and modifies the verb читаю (“I am reading”).

Why not say более долго?

Russian prefers the synthetic comparative дольше. Более долго is grammatically possible but sounds clunky and is rarely used in everyday speech. Use дольше here.

Why is there a comma before чем?

In comparisons with чем (“than”), a comma before чем is standard: … дольше, чем …. Your sentence follows the usual punctuation norm.

Can I drop чем and say дольше вчера?

No. With adverbs like вчера (“yesterday”), you need чем. The genitive-of-comparison (e.g., дольше тебя) works with nouns/pronouns, not with adverbs such as вчера.

Can I expand чем вчера to a full clause?

Yes: Сегодня я читаю дольше, чем я читал вчера. The shorter чем вчера is an ellipsis of that full clause and is more natural.