Learn Hardcore Russian: Физика сложнее, чем я думал, но интересна. - Physics is more difficult than I thought, but interesting.

сложнее is the comparative form of the adjective сложный (complex, difficult). In Russian, to say that something is “more X than Y,” you change сложный to сложнее. So Физика сложнее means “Physics is more complex/difficult.”

Why do we say чем я думал and not include a noun after чем?

In Russian comparatives, чем (“than”) can introduce a full clause, not just a noun phrase. Here, чем я думал literally means “than I thought.” There’s no need for another noun because the clause itself (“I thought [it]”) completes the comparison.

Why is there a comma before чем?

Russian punctuation rules require a comma before чем, when it introduces a subordinate clause in a comparison. So you separate сложнее and чем я думал with a comma, just as you would in English: “more complex, than I thought.”

Why is there no verb in но интересна? In English we’d say “but it is interesting.”

Russian often drops the present-tense form of быть (“to be”). In predicates with adjectives, you simply say the adjective. So интересна stands for (она) интересна (“it [she] is interesting”), with the subject understood from context.

Why is интересна in the feminine form?

Adjectives in Russian agree with their nouns in gender, number, and case. Физика is a feminine noun, so its predicate adjective интересна also uses the feminine ending -а.

Why is there a comma before но?

In Russian, as in English, coordinating conjunctions like но (“but”) typically have a comma before them when they connect two independent clauses or contrasting predicates. Here, “сложнее…” and “интересна” are two predicates being contrasted.

Could the sentence be Физика сложнее, чем я думал, но она интересна? Would that change the meaning?

Yes, you can say но она интересна. Adding она explicitly names the subject (“but it is interesting”). The meaning stays the same; the version without она is just more concise and common in Russian.

Is it possible to use интереснее instead of интересна?

You could say Физика сложнее, чем я думал, но интереснее, meaning “Physics is more complex than I thought, but more interesting.” However, that changes the comparison: now you compare interestingness to something else (implied) rather than simply stating it’s interesting. Use интересна for “it is interesting” without adding a second comparison.