In his new book, Cat Sense, British biologist Dr. John Bradshaw describes the way that cats think of their owners and other humans as: "larger, non-hostile cats."

Bradshaw, who's been studying cat behavior for over 30 years, claims that cats still live in a semi-wild, semi-domesticated state.  Unlike dogs, who have been deliberately bred by humans for specific purposes, cats have always been free to breed however, and with whoever they'd like, granted that they haven't been fixed.

According to Bradshaw, 85 percent of cats are bred with feral cats, since the domestic cat population is mostly regulated through spaying and neutering. 

Really, cats only live with humans because they've domesticate themselves.  They figure out that there's a replenishing food source at their owner's home and continue to come back for that very reason.  Because cats are cute and, historically, because they kill mice and other rodents that can pose a threat to crops, humans have accepted this relationship.

So if cats choose to hang around our homes, they're still going off of instinct, and instinct tells them we are just: "larger, non-hostile cat."

Not only that, but cats actually behave towards humans the way they do towards their mothers, since that's the most significant relationship a cat has had with a larger, non-hostile, cat.

In an interview with NPR, Bradshaw explained the reason cats purr: "It starts off with kittens purring to get their mother to lie still while they're suckling, and it goes on into adulthood. ... It's a signal to the animals, [and] the people around them to pay attention and try to help them."

Other cat behaviors, like kneading, can be explained in the same way.  Cats knead their owners because this an action they perform on their mothers to obtain breast milk.  Also, he says that outdoor cats bring dead bird to their owners doorstep because they're trying to share.

It remains unseen what cats think of dogs.