Он молчал, ибо не знал ответа.

He was silent, for he did not know the answer.

Breakdown of Он молчал, ибо не знал ответа.

• не: not
• ответ: the answer
• он: he
• знать: to know

Questions & Answers about Он молчал, ибо не знал ответа.

Why are молчал and знал both in the past tense?

Because the sentence describes a situation in the past: He was silent, for he did not know the answer.

Both verbs are past tense singular masculine forms:

• молчал = was silent / kept silent
• знал = knew

They agree with он (he), so they take masculine singular past forms.

Why do the past tense verbs end in -л?

In Russian, past tense verbs are commonly formed with -л plus gender/number endings:

• masculine: usually just -л → молчал, знал
• feminine: -ла → молчала, знала
• neuter: -ло → молчало, знало
• plural: -ли → молчали, знали

So молчал and знал are masculine because the subject is он.

What does ибо mean, and is it common in modern Russian?

Ибо means for, because, or since in a rather formal, literary, or elevated style.

So:

• Он молчал, ибо не знал ответа. = He was silent, for he did not know the answer.

In everyday modern Russian, people are much more likely to say:

• Он молчал, потому что не знал ответа.

So a learner should recognize ибо, but not expect to use it much in casual conversation.