Я не могу дотянуться до книги на верхней полке.

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Breakdown of Я не могу дотянуться до книги на верхней полке.

• книга: the book
• на: on
• не: not

Questions & Answers about Я не могу дотянуться до книги на верхней полке.

Why is the verb дотянуться used here, and what does the -ся ending do?

Дотянуться means to be able to reach as far as something, often by stretching your arm or body.

The -ся ending makes it a reflexive verb, but in many cases like this, it is best learned as part of the whole verb rather than translated literally as oneself.

• тянуть = to pull, to stretch
• тянуться = to stretch oneself / reach out
• дотянуться = to reach all the way to something

So дотянуться до книги means to reach the book in the sense of physically being able to stretch far enough.

This is different from a direct-action verb like взять (to take) or достать (to get / take down).

Why is it не могу дотянуться, with an infinitive after могу?

Because мочь means can / be able to, and like English can, it is followed by another verb.

• Я могу = I can
• Я не могу дотянуться = I can’t reach

So the structure is:

• я = I
• не могу = cannot
• дотянуться = reach

This is very normal Russian grammar: a conjugated modal verb + infinitive.