There are three points to make in response to the question in the title. The first point is that you want your cat to scratch something! This is because it is natural cat behaviour and you want your cat to express his or her natural behaviour because it makes them more content (feline mojo). The second point is that you have to try and discourage your cat scratching objects that you don’t want them to scratch. The third point is that you have to encourage your cat to scratch objects that you want them to scratch.
Scratching is natural behaviour
Cats scratch to stretch their backs and their legs, to deposit scent on the object and to remove the outer layer of keratin from their claws to sharpen them. It’s all completely normal and natural. It’s a confident form of territorial marking compared to peeing on the corner of the couch. So you accept scratching and you do this before you adopt a cat. Furthermore, you don’t stop it by declawing your cat because that is cruel.
Discouraging scratching furniture and carpet
It’s easier to discourage a cat from scratching the corner of an armchair or sofa compared to a carpet. You can discourage scratching a piece of furniture in two ways. Firstly, you can put things such as double-sided tape onto the place where they scratch. I think you can buy special tape for this specific purpose. An alternative to this temporary deterrent would be tinfoil. Cats get really perturbed by tinfoil. It needs to be stressed that this is temporary and part of an overall strategy. The second way to discourage scratching furniture is to put a super-solid scratching post in front of or near the item of furniture being scratched.
Encourage scratching scratching board or scratching post
Cats like to scratch your favourite armchair because there’s lots of you on it, by which I mean your scent and of course it is solid. You may already have a scratching post but it is likely to be too small and not stable enough. It should be as solid as a tree trunk and of course as solid as an armchair.
There is only one such product in my book and you can buy on Amazon. In the UK it is called the Smart Cat Ultimate Scratching Post. It is the only product that I know of on Amazon of any kind which gets a five star rating from almost 14,000 reviews. That’s remarkable. It costs £34.99 plus delivery charges. In America they have an all-grey version of this post called the Smart Pioneer Pet Ultimate Scratching Post which gets a 4.5 out of 5 rating out of 15,000 reviews. The American one costs $69.99. It is genuinely a solid product which mimics the trunk of a small tree. I’m not getting commission for recommending these products by the way! I have one plus some scratching boards.
You should put cat nip on it and rub your scent on it as well using dirty clothing. The latter may work better than the former.
Discourage scratching the carpet
It is harder to discourage a cat from scratching the carpet because it may be quite a large area and you can’t cover it in double sided tape or foil. The only solution here is to encourage the use of scratching boards. If your cat likes to scratch carpet it’s possible that he or she prefers to scratch horizontally. In which case he will prefer to scratch a scratching board (possibly). He may scratch both board and post equally. Mine does. You can buy cardboard horizontal scratching boards on Amazon at a very reasonable price. I would buy half a dozen and place them at strategic points. Catnip comes with them so you can sprinkle catnip on the board and he should use it immediately both to scratch and lie on because of the catnip.
There’s one extra thing that you can do which is to praise your cat if he uses the scratching post. You can do this by warm words and a treat after he has done it. Praise him many times.