Я так и не смог открыть вложение и попросил переслать письмо ещё раз.

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Breakdown of Я так и не смог открыть вложение и попросил переслать письмо ещё раз.

• открыть: to open
• и: and
• смочь: to be able

Questions & Answers about Я так и не смог открыть вложение и попросил переслать письмо ещё раз.

What does так и не add to the sentence?

Так и не is an idiomatic pattern that adds the idea of in the end, it still didn’t happen or never did happen.

So:

Я не смог открыть вложение = I couldn’t open the attachment.
Я так и не смог открыть вложение = I never managed to open the attachment / I still couldn’t open it in the end.

It often suggests that the speaker expected the action to happen, or tried, but the result never came.

Very common examples:

• Я так и не понял = I never did understand.
• Он так и не пришёл = He never ended up coming.
• Мы так и не встретились = We never did meet.

Why is it смог, not мог?

Смог is the past tense of смочь, which is the perfective partner of мочь.

The difference is roughly:

• мог = could / was able to, in a general or ongoing sense
• смог = managed to / succeeded in being able to

In the negative:

• не мог открыть can mean was unable to open
• не смог открыть more strongly means did not manage to open

In this sentence, не смог fits well because the speaker is talking about a specific failed result: the attachment did not get opened.

Why is the infinitive and not ?