Over the course of evolution, purring has probably offered some selective advantage to cats. Most felid species produce a "purr-like" vocalization. In domestic cats, purring is most noticeable when an animal is nursing her kittens or when humans provide social contact via petting, stroking or feeding.
No one knows for certain why cats purr, though it is believed to be a voluntary act initiated by the central nervous system. They typically do it when they are petted and it's kind of their way of saying thank you and it feels good.
cats purr for several reasons-they are happy, they are hurt, they like you. try looking at your cat and see if there any other signs of how it is feeling. does it look at you and slowly blink? that is a sign that it likes you. try looking at your cat and slowly blink your eyes at it. see if it does the same thing.
A cat's purring originated as a means of communicating from kitten to mother (and vice-versa) without it being heard by others (namely predators and other adult male cats who did not father the kittens).
A cat purring is usually a sign of contentment, but it can also be a means of relieving stress and trying to be calm.
5 months ago
Last edited at 12:42PM on 7/2/2013
Perhaps not always so, thefoo, I have one brother & sister cat from a litter of six, both of whom also purr when they're nervous - like when I'm holding them to petromalt or de-flea them and they both know when it's coming! (they are very trusting not to fight or flee)
cats purr because just like hunmans when we get excited we breath faster well the same thing goes for cats and the air ripples their throat and sound flap as i call it and it makes the so called purring sound
Pretty much all of the comments here are only partially correct. It is true that they purr because they are content but cats also purr when they are frightened and angry. Purring is a bit like smiling for us humans. We smile when we are nervous, happy, and when we want something. Same goes for cats.