Frankfurt: "Human beings are not alone in having desires and motives, or in making choices. They share these things with members of certain other species ... It seems to be peculiarly characteristic of humans, however, that they are able to form ... 'second-order desires ...'

So cats and dogs etc. have desires and act from desires. A dog can want (desire) a biscuit and bark in order to get a biscuit. So can humans. A dog can even have conflicting desires (as can humans). (The dog might desire the biscuit but also desire not to come inside, and recognize it will not get a biscuit unless it comes inside.) But humans can also have second-order desires. A human can desire not to have a desire for a biscuit. A dog, Frankfurt suggests, cannot desire to have, or not to have certain desires. A dog cannot desire that its first-order desires be, or not be, effective.