Учитель объяснил правило ясно.

The teacher explained the rule clearly.

Breakdown of Учитель объяснил правило ясно.

• учитель: the teacher
• объяснить: to explain
• правило: the rule
• ясно: clearly

Questions & Answers about Учитель объяснил правило ясно.

Why is ясно an adverb here and not an adjective?

ясно is the adverb form of the adjective ясный. In Russian, many adjectives form adverbs by replacing the ending -ый/-ий with -о (or -е). Here ясно answers the question “How did he explain?” (как?), so it must be an adverb.

What case is правило, and why doesn’t it change its ending?

правило is in the accusative case as the direct object of объяснил. Since правило is a neuter inanimate noun, its accusative form is identical to its nominative form.

Why is the verb объяснил in the perfective past tense, and how would it differ from the imperfective?

объяснил is perfective, indicating a completed action (“explained” once). The imperfective counterpart is объяснял, which suggests an ongoing or repeated action (“was explaining” or “used to explain”). So:

• Учитель объяснил правило ясно. → The teacher explained the rule clearly (one time).
• Учитель объяснял правило ясно. → The teacher was explaining the rule clearly (over a period of time).

Where does the stress fall in объяснил and правило?

• объяснил is stressed on the second syllable: об-ЛЯ́С-нил ([əbʲˈlʲɪsnʲɪl]).
• правило is stressed on the first syllable: ПРа-ви-ло ([ˈpravʲilə]).

Why is there no article like “the” or “a” before учитель or правило?

Russian does not use articles. Context alone tells you whether something is definite or indefinite.

Could I say Учитель ясно объяснил правило instead, and does it change the meaning?

Yes, Учитель ясно объяснил правило is also correct. Placing ясно before the verb slightly shifts the emphasis onto the manner of explanation, but the overall meaning (“The teacher explained the rule clearly”) remains the same.

Why is there no preposition before правило? In English we say “explain something,” but in other contexts Russian uses prepositions.

In Russian, объяснять/объяснить takes a direct object without a preposition when you “explain something.” You only use a preposition (like о) when you explain about something: объяснять о правиле (“to explain about the rule”), which is a different construction.

Can I replace ясно with понятно, and will the nuance change?

You certainly can: Учитель объяснил правило понятно. понятно also means “understandably/clearly,” but it sometimes carries more of a sense “so that it is understood.” ясно emphasizes clarity and lack of ambiguity, while понятно emphasizes that the listener can understand.