The following is translation of a text I originally wrote in German. With grateful thanks to Allegra Loch (Tonkinini Tonkinese), who edited, tweaked and overall improved the text to make it suitable for an English audience.

Again and again I receive calls from people who want to have & keep a single cat, and preferably a kitten. These days I block them off pretty quickly, but in the past I've always tried to explain that cats, contrary to stubbornly persistent popular belief, are social animals in need of contact with conspecifics (animals belonging to the same species).

As far as outdoor cats are concerned, they have the opportunity to maintain social contacts outside the home, but more and more cats are kept as indoor cats only for a variety of sensible reasons, and they have no choice.

Schlafhöhlen-Einsatz für Kallax-Regal
Cat cave for IKEA cabinet KALLAX

Before I go into the various reasons that are mentioned to me why it should imperatively be a single cat, I would like to point out the legal situation in the country where I live, Switzerland. On the one hand, the Animal Welfare Ordinance stipulates that all social species must necessarily be given a conspecific species (TSchV 455.1 Art. 13), but on the other hand in the case of dogs and cats it allows the conspecific be replaced by a human (which, of course, is not possible). Especially in the case of very social breeds, which include all Oriental breeds such as Siamese, Balinese, Oriental Shorthair and Longhair, Burmese, Tonkinese, Thai and Korat. In my experience a social partner of the same species is absolutely necessary. It does not necessarily have to be a cat of the same breed, but it should be of similar temperament, meaning it should be playful, affectionate and intelligent. Nothing can replace the in depth play, grooming and social interaction that their own species can provide.
The fact that cats are inherently social animals is also supported by a growing body of research that looks at the social interactions within semi-feral cat populations. Behavioural researchers have found that as long as resources like food and shelter are readily available, cats prefer to live in groups or colonies that are organized along female-centered lineages, sometimes even participating in communal nursing among related females. Thus the myth of the domestic cat as a solitary species has been largely dismantled by scientific studies over the last few decades (for an overview see 
The Domestic Cat. The Biology of its Behaviour, ed. by Dennis C. Turner and Patrick Bateson, Cambridge UP, New York 2014, 3rd edition)

One argument that I always hear is that the predecessor cat was also a single cat and happy that way. I always wonder how the owners know that; did the cat tell them that? Of course not, but they probably infer it from the fact that the cat has not shown any behavioral problems despite the lack of social contact to conspecifics. One thing I've learned in over 30 years of living with cats, is that cats are extremely accommodating and can adapt very well to the circumstances in which they are kept. They are also extraordinarily capable of suffering in silence, and it takes a lot of time for cats to show their suffering (be it psychological or physical) to the outside world. So, if a cat does not display any symptoms, that does not mean that it does not suffer. Cats are designed in the wild to not show any weakness or illness, as predators will pick up on these signals, therefore it takes a huge amount for a cat to give outward signs. 

However, there are often subtle indicators that the cat does not feel completely well: loud, incessant meowing, scratching in unwanted places, and in the worst case even uncleanliness.
It is also understandable that cats that have been kept as only cats for a very long time become loners and are not necessarily pleased when, after years of enforced loneliness, they are suddenly confronted with a play buddy without warning. But even after years without a cat company, the majority of cats are happy about a play buddy, as long as one makes sure to introduce them slowly and carefully to each other.

Screened cat window
Screened cat window

Another argument that I often encounter is lack of space. My answer is always the same: where there is room for one cat, there is room for two cats. For a cat enclosure / cat room, the animal welfare ordinance already cited (Appendix 1, Table 11) requires a minimum area of 7m2 for 1-4 cats (plus 1.7m2 for each additional cat). Of course, the minimum requirements primarily applies to animal shelters or a separate cat room (for instance for keeping a stud cat). The more room, the better, but I think cats can be happy even in a relatively small space (for example a one-room apartment) if they are designed especially with the needs of cats in mind. For me it goes without saying that cats should have access to all rooms in the apartment. Also, the space for cats can be extended, if you include different levels and make use of the vertical dimension: here, for example, a room-saving floor-to-ceiling scratching tree or a scratching post fastened to a wall  is a good solution, maybe combined with a cat shelf just below the ceiling. Or you can provide a climbing aid onto the wardrobe, where the cat can withdraw to snooze. Also, a sleeping cave in the bookshelf will be gladly accepted, or a radiator hammock. Furthermore, if you make the balcony accessible and safe, the cats will not only be able to enjoy fresh air, but can also be entertained by observing their surroundings. Even if there is no balcony, you don’t need to be a master handyman to build a removable peep-box for a window and thus create a welcome viewing platform. The Facebook Group Kitty Gardens, Catios, House Cats and Catification  has some excellent ideas & resources for indoor cats, for all sizes and layouts of homes and to suit all budgets.

Ferris cat wheel providing exercise and fun (photo: Allegra Loch)
Ferris cat wheel providing exercise and fun (photo: Allegra Loch)

Still another excuse that is often cited is the lack of money. Strangely enough, it is usually about the supposedly high purchase costs of a purebred cat and rarely about the recurring monthly expenses. But even if no unscheduled veterinary costs are incurred, the average upkeep of a cat over its lifetime surpasses the purchase price many times over. As mentioned above, you do not necessarily have to adopt two purebred cats and if you are not fixated on two kittens, many breeders are from time to time also looking for a suitable home to place adult cats, be it for a former breeding queen (stud) or because tensions have developed in a cat group for whatever reason. A good combination is therefore to adopt a kitten with its mom. As far as the monthly expenses are concerned, it is true that the upkeep of two cats is more than for one, but by no means twice as much. Cat accessories like a scratching post, cat beds or toys don’t need to be purchased in duplicate. With cats that get along well, one slightly larger transport box is enough, which is better anyway, as the presence of a companion provides comfort and has a calming effect. With regard to food you also save by being able to buy larger packaging sizes; the same food costs considerably less in the 400g can than in the 200g can (calculated at 100g).

As a long-time cat owner the next argument makes me particularly upset: more than one prospective kitten buyer told me "I want my cat to be attached to me and not to another cat." Not only is this attitude extremely selfish, but it also reveals a frightening lack of empathy for animals in general and the needs of cats in particular. When keeping pets, it should not only (or even primarily) be about the needs of the human owner, but about how to provide a stimulating and appropriate environment to make the life of one’s four-legged roommates as agreeable as possible, especially if due to hazards outside (traffic, etc.) you can’t let them roam free. I can understand the desire for a cuddly, affectionate cat, but you cannot force affection. If you want a cat to cuddle, you should choose a breed that closely bonds with their humans, like an Oriental breed. Any owner of two (or more) cats of an Oriental breed will confirm that they are just as attached to and affectionate towards their owners when they are kept as a pair or in a group. If you live with such cats, you're never alone, because they want to be close to their human anytime, anywhere: in the bathroom, while cooking, making beds, working on the computer or having a cozy evening in front of the TV. No matter where you are, you are usually besieged by several cats as soon as you sit down. So, how absolutely selfish do you have to be to begrudge your cat the companionship of another cat.

Human beleaguered by a bunch of Tonks (photo: Allegra Loch)
Human beleaguered by a bunch of Tonks (photo: Allegra Loch)

If, despite all the sensible arguments put forth, you still desire to keep only a single cat, then NEVER a kitten. You may occasionally find adult cats advertised in animal shelters or on rescue sites on the internet that do not get along with other cats. Usually that is due to a lack of proper socialisation, their origins or their temperament; then you should definitively give such a cat a chance. But please don't damn a social, outgoing, playful, affectionate kitten to a life of loneliness, but rather rejoice in the heart-warming picture of two (or more) cats snuggled together!