To the cat lover there may be no such thing as too many cats, but to some cats the old adage “the more the merrier” just doesn't ring true. Compatibility depends on the cats themselves and on the particular situation. Some cats are most happy as “only cats” while others enjoy feline company, provided that introductions are well managed and there are sufficient resources to go around. Why the difference? As you might guess, both nature and nurture factor into the equation.
Rudyard Kipling immortalized the stereotype of the cat who walks by himself - and for good reason. Except at certain times of their lives, like mating, mothering, and as kittens, cats seem to be pretty self-sufficient, and in nature spend many hours on their own. The natural state of a cat is solitary and social interactions must be carefully engineered.
One reason for your cat's natural solitude is that they are lone hunters, not pack hunters like dogs. Their natural prey comes in individual meal-sized packages like a mouse, and a pack of cats hunting a mouse wouldn't get much of a meal at the end of the chase. So cats just go it alone relying on stealth and pouncing skills rather than sheer weight of numbers. But studies have shown that when resources are plentiful, for example, at docksides or on farms, cats do manage to dwell happily together in a true society and cooperate with each other to raise their young.
Like the young of other species, kittens can be persuaded that almost any creature can be their friend if they are benignly exposed to them during the sensitive period of their development between 2 and 7 weeks. During this period kittens can learn that mice or doves should not be regarded as prey items. Natural fears also can be eased in a most impressive way. In order for this to happen, however, the mother cat must have the same attitude because kittens learn by observation - including what to be concerned about. Secondly, the creature, whether it is a bird, mouse, or unfamiliar cat, should behave calmly so as not to raise fur or cause any harm. Raised among many friendly cats, your cat will become fully at ease in the company of other cats and will turn out to be a social success - a good mixer.
However, a cat that is raised by a skittish mom, or who doesn't meet many other cats during the first 7 weeks of his life, will always be suspicious, reclusive, even hostile around cats later in life. Also, one really catastrophic encounter with a hostile cat will affect an otherwise friendly cat's perception of other cats, or at least cats that are similar to the offender.
How Many Then?
The Ideal Situation
The ideal situation would be a large group of cats coexisting peacefully as a one big happy family. It can happen but you have to know what you're doing. First of all you start with a stable group of friendly cats.
Using this technique, it is possible, for those so inclined and with time on their hands to do the cats justice, to amass some 6 or 8 cats within the area of a large house. But beware, such a family will cost a fortune in cat food and cat litter, your vet bills will be exorbitant, and it will take about an hour a day to scoop the boxes and interact with each cat. Although you might think that neutering of males would be an essential requirement for the peaceful coexistence of such a large number of cats, actually it isn't. However, neutering is a must to prevent the huge number of kittens that would otherwise result.
So, how many cats are too many? That depends. It depends on genetics, on socialization and on facilities and protocol. For most people, two to three cats are enough. For others 5 to 10 might be manageable. For the occasional feline aficionado with time, the patience of a saint, and money to burn, even larger numbers of cats can be successfully managed.
But don't fall into the collector trap. These individuals collect great numbers of cats thinking that they are doing the right thing. This isn't always true, and they are blind to the squalor and suffering they propagate. Collectors may have a form of obsessive-compulsive behavior, but whatever the situation it is important for them to realize their limitations and their predicament. For them the magic number should be zero.