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?