Questions & Answers about Вчера я купил фиолетовый блокнот.
Why does the sentence start with вчера? Can the word order change?
Yes, the word order can change.
Russian word order is more flexible than English because grammatical endings carry a lot of the meaning. Вчера я купил фиолетовый блокнот is a very natural way to say Yesterday I bought a purple notebook.
You could also say:
- Я вчера купил фиолетовый блокнот.
- Фиолетовый блокнот я купил вчера.
These all mean basically the same thing, but the emphasis changes:
- Вчера first puts focus on when
- Я first puts a little more focus on who
- Фиолетовый блокнот first emphasizes what was bought
So the original sentence is normal and common, especially if you are introducing the time first.
Why is it купил and not something else?
Купил is the past tense masculine singular form of the verb купить, which means to buy.
Russian past tense usually agrees with the gender and number of the subject:
- я купил = I bought (said by a male speaker)
- я купила = I bought (said by a female speaker)
- мы купили = we bought
- он купил = he bought
- она купила = she bought
- они купили = they bought
So купил tells you that the speaker is male, or at least that the sentence is being given in the masculine form.