The Language of Cats
Many people believe that language is the domain of human beings. However, cats have developed an intricate language31 not for each other, but for the human beings who have adopted them as pets.32
When communicating with each other, cats' "talk" is a complex system of nonverbal signals.33 In particular, their tails, rather than any kind of "speech," provide34 cats' chief means of expression. They also use physical contact to express their feelings. With other cats, cats will use their voices only to express pain. 
Next, incredibly,36 all of that changes when a human walks into the room. Cats use a wide range of vocal expressions when they communicate with a person, from affectionate meows to menacing hisses. Since cats verbal expressions37 are not used to communicate with other cats, it is logical and reasonable38 to conclude that cats developed this "language" expressly to communicate with their human owners.
This fact is demonstrated more clear since39 observing households that have only one cat. An only cat is usually very vocal, since the only creature around with whom the cat can communicate is its owner. Cats with other feline companions, though, are much quieter. If they want to have a conversation, they need only go to their fellow cats and communicate in their natural way. 
Since cats learned to meow for the sole purpose of communicating with human beings, owners should take the time to learn what their different meows mean. If an owner knows, to41 name just a few examples, which meow means the cat is hungry, which means the cat wants to be petted, and which means the cat wants to have a little "conversation," the bond between cat and owner will grow deeper.
Certainly, after a time, owners will see that communicating with their pets, not just cats, is every bit as important to forging good relationships as to communicate43 with other humans. Once, as an owner, you know that the cat is not just making senseless noises without any rhyme or reason44 but is making an attempt to communicate, you can make an effort to communicate back. After all, your cat isn't meowing just for the sake of making noise; however, cats are less communicative than many other animals.45