Cecil takes the political route and gives the following answer:
Judging the relative intelligence of cats and dogs is like deciding which is better looking — there's just not much basis for comparison. Psychologists have a tough enough time coming up with a culture-blind IQ test for humans, who all belong to the same species; designing a species-blind test for dogs and cats is just about impossible. What people take to be signs of intelligence in their pets usually are just specialized survival skills that say nothing about innate brainpower. A cat, for instance, is much more dexterous with its paws than a dog. This dexterity fascinates cat lovers, who also cite the cat's legendary standoffishness as proof of its mental superiority. The dog, on the other hand, is much more of a social animal; dog advocates claim this proves the dog is more civilized, ergo, more intelligent.
This reminds me of Howard Gardner's theory of multiple intelligences. Nobody's really smarter than anybody else. Some people are good and some things, like music and swimming, and others are good at writing poems and solving geometric proofs.
That is to say, there are some people who consider intelligence a wholly subjective concept, and others, such as myself, who consider it an objective concept, amenable to defining and measuring without regard to value judgment.
Instead of talking about two individuals or species that are relatively close in their cognitive capacities, let's take an extreme example to illustrate the point and ask:
Which is more intelligent, an earthworm or a chimpanzee?
There are two broad ways to answer this question. The first is to do so as Cecil did, under the idea that intelligence is subjective and relative to the individual or species. In that case, we would say that the question is nonsensical. An earthworm is good at burrowing and detecting various nutrients in soil. A chimpanzee is good an living a semi-arboreal lifestyle and all that that entails. I personally think this is a silly response. That particular answer negates the concept of intelligence as relating to cognitive capacities, and instead more closely associates it with the concept of evolutionary fitness.
The more sensible answer is the one that I think most scientists and laypeople would give if pressed for an answer, the obvious one: the chimp. And why? Well, those same people might be hard pressed to justify their answer, and as I've blogged about before, there's a paucity of good theory relating to intelligence, especially across species and systems.
Personally, I'd say that intelligence is the collective capacity of a system to recognize patterns (temporal and spatiotemporal), generate patterns, and in some cases learn patterns. An individual's ability to do so is dependent upon the number and quality of their sensory modalities (vision, hearing, touch, etc.) and the range and complexity of their behavioral repertoire. We can measure an individual's ability to recognize, generate, and learn patterns, both in naturalistic and controlled settings by observing four main metrics:
- breadth: how many different kinds of patterns can they recognize/generate/learn?
- depth: how many patterns within a given class can they recognize/generate/learn?
- speed: how fast can they recognize/generate/learn patterns?
- accuracy: how well can they recognize/generate/learn patterns?
In terms of its ability to perceive and process its environment, a chimpanzee has far more powerful and numerous sensory systems than an earthworm. Also, the range of behaviors that a chimpanzee can perform vastly outnumbers those of an earthworm. Even without any quantitative assessment, it's very easy to see that by these criteria a chimpanzee is more intelligent than an earthworm.
I think an answer exists to questions like: Is person A more intelligent than person B? and Which is more intelligent: cats or dogs?
In the case of species with numerous breeds, the answer may be complex. But I believe there is a practical way to determine whether or not the mean intelligence of a given species is greater or less than that of another. What is needed first is a strong theoretical framework, followed by the development of rigorous tools and methods to make those determinations, and right now we are sorely lacking in both.