Rationality is often seen as the ability of a being to measure, to plan for the future, and to think of steps and instruments needed to reach a goal. While all of these are doubtless neccesary for the full expression of human rationality, they all depend on one faculty: the ability to think objectively. In order for a mind to be able to measure or plan for the future, it has to escape the world of sense impressions and think about things objectively, including itself.
This protorational ability to think in objective terms is certainly not reserved to human beings : a great many mammals seem to posses it. I use the cat as an example. I could also use the horse or the dog, but cat's behavior is easier, and much more amusing, to search for signs of self-objectivizing. It seems clear, unless we take on a position of exteme skepticism regarding the ability to deduce mental states from behavior, that cats experience such emotions as embarassment, vanity, pride and nervousness. All of these emotions require the cat to look at how they look in another eyes. When a cat falls asleep on the edge of a cabinet, and falls to the ground, only to pick themselves up and begin grooming themselves, it is not because of anything in their subjective sense expression that they are reacting to, but rather to the idea of how they look in your eyes: they are not concerned with immediate pleasure or pain, but rather with the idea of how another person is viewing them as an object. Cats well-known vanity, their concern with how neat and well groomed they are, is another example of the feline ability to view themselves as an object through another's eyes.
This is very interesting from a cognitive point of view. The ability to leave behind their momentary impressions and to focus on the fact that "others" exist and that they exist in other's eyes is quite a set of abstractions away from a cthonic blur of sense impressions. Of course, I don't know if cats are "thinking" of these steps in the way we think of thinking, but overall it is clear that cats can orient their viewpoint away from what is in their immediate sense data.
I bring this up not because I am interested in felines, or mammals in general as such. I mention it because it underscores a distinction often elucidated in moral and psychological writings that is in many ways is not totally true. One of the most traditional descriptions of both a moral person and a psychologically mature individual is the ability to ignore their sense impressions and to put themselves in another's shoes. But, as we have seen with cats, the ability to place themselves in another's shoes is present even in amoral animals such as cats, let alone in people. In fact, some of the most immoral people commit acts of immorality not based on following their immediate sense impressions, but based on how they think others are viewing them as objects. An example would be the infamous Spurs Posse. They did not rape teenage girls because they were transfixed by the momentary sexual pleasure involved, but because they viewed themselves as objects in other's eyes, and were motivated by wanting to look good in those people's eyes. It was this objective nature of their behavior that drove them to collect "points", an objective measure of their success.
The ability to think objectivly, to be guided by an image of yourself from the outside, is not limited to humans, let alone limited to people of the Age of Reason. It seems to extend fairly far down into the mamallian kingdom. Not only that, but the ability to think objectivly seems to be rather unrelated to morality or the ability to think in a mature manner.