Мы купили кошке когтеточку, чтобы она не царапала диван.

Because кошка is the recipient/beneficiary of the thing being bought.

In Мы купили кошке когтеточку, the structure is basically:

• Мы = we
• купили = bought
• кошке = for the cat / to the cat
• когтеточку = a scratching post

Russian often uses the dative case where English uses for:

• купить ребёнку игрушку = to buy a child a toy
• сварить другу кофе = to make a friend coffee

So кошке means for the cat, not the cat as a direct object.

Because it is the direct object of купили — it is the thing that was bought.

The dictionary form is когтеточка. In the sentence, it becomes когтеточку because feminine nouns ending in -а / -я usually change to -у / -ю in the singular accusative:

• книга → книгу
• машина → машину
• когтеточка → когтеточку

So:

• кошке = for the cat
• когтеточку = the scratching post

Когтеточка is a common Russian word for a cat scratching post / scratching pad / scratching board.

It comes from:

• коготь = claw
• точить = to sharpen

So the idea is something a cat uses to sharpen its claws.

This is one of those words that may not have a perfect one-word English equivalent, so translations can vary:

• scratching post
• scratching pad
• cat scratcher

Here чтобы introduces a purpose clause. It means something like:

• so that
• in order that
• so

So:

Мы купили кошке когтеточку, чтобы она не царапала диван.
= We bought the cat a scratching post so that she wouldn’t scratch the sofa.

This is very common in Russian when talking about purpose:

• Я пришёл, чтобы помочь. = I came to help.
• Мы закрыли окно, чтобы не было холодно. = We closed the window so that it wouldn’t be cold.

This is one of the most common learner questions, and it is very normal to be confused by it.

After чтобы, Russian often uses the past-tense form of the verb, but the meaning is not necessarily past. It often expresses:

• purpose
• desired result
• something intended
• something hypothetical

So чтобы она не царапала диван means:

• so that she wouldn’t scratch the sofa
• so that she doesn’t scratch the sofa

It is not saying she scratched it in the past. It is just the normal grammar pattern after чтобы.

Compare:

• Я открыл окно, чтобы было прохладнее. = I opened the window so that it would be cooler.
• Мы говорим тихо, чтобы ребёнок не проснулся. = We speak quietly so that the child doesn’t wake up.

Because the idea is preventing repeated or ongoing scratching in general, not preventing one single completed act.

Царапать is imperfective, which fits well here because the meaning is:

• so that she wouldn’t scratch the sofa
• so that she would stop scratching / not keep scratching the sofa

A perfective form would suggest a more single, bounded action. In this sentence, the imperfective is more natural because cats scratch furniture as a habitual behavior.

So the sentence is about avoiding a general behavior, not one isolated scratch.

Диван is masculine singular and inanimate, so in Russian its accusative is the same as its nominative.

That is why:

• nominative: диван
• accusative: диван

This is normal for many masculine inanimate nouns:

• стол → вижу стол
• дом → строим дом
• диван → царапала диван

By contrast, masculine animate nouns often change in the accusative:

• кот → вижу кота
• брата from брат

So диван is accusative here, even though it looks unchanged.

Она refers to кошка — the cat.

That is why it is feminine singular:

• кошка is feminine
• so the pronoun is она

The meaning is:

• We bought the cat a scratching post so that she would not scratch the sofa.

In English, you might say it for an animal, but Russian often uses the grammatical gender of the noun:

• кошка → она
• кот → он

Not naturally in this sentence.

Russian can sometimes omit subjects when they are clear from the verb form, but here царапала is a past-tense form, and past tense in Russian agrees with gender and number, not person in a way that would clearly identify the subject by itself.

So чтобы не царапала диван would sound incomplete or much less clear on its own in standard usage. Including она makes it explicit that the cat is the one who might scratch the sofa.

Both are possible. Russian word order is more flexible than English.

The version in your sentence sounds very natural and can slightly emphasize for whom the thing was bought:

• Мы купили кошке когтеточку = We bought the cat a scratching post.

You could also say:

• Мы купили когтеточку кошке

The meaning stays basically the same, but the focus can shift a little depending on context.

Russian word order often reflects:

• what is already known
• what is being emphasized
• what sounds most natural in context

So this is more about information flow than a strict grammar rule.

Yes, but it is not exactly the same in tone or structure.

• Мы купили кошке когтеточку = We bought the cat a scratching post.
• Мы купили когтеточку для кошки = We bought a scratching post for the cat.

Both are grammatical. But with verbs like купить, Russian very often prefers the dative when talking about the person or animal who receives or benefits from the item.

So кошке is especially natural here.

Using для кошки is also possible, but it sounds a bit more explicitly like for the cat, whereas кошке fits the common double-object-style pattern.

Because Russian has no articles.

So nouns like кошка, когтеточка, and диван do not automatically include words like a, an, or the. The listener understands the meaning from context.

For example:

• Мы купили кошке когтеточку could mean We bought the cat a scratching post
• In another context, it might be understood as the scratching post

English requires articles; Russian does not.

If you translate word-for-word, it may look something like that, but that is not how you should understand it.

A more natural way to read the structure is:

• чтобы = so that / in order that
• она не царапала = she wouldn’t scratch / she doesn’t scratch
• диван = the sofa

So it is better to think in terms of the whole pattern, not literal English matching.

This is a good example of why Russian subordinate-clause grammar should be learned as a construction, not word by word.