I bought this book when I casually bumped into it in a bookshop. I was immediately captured by its intriguing title. The western culture we live in considers the rationality of emotion as absolute nonsense. (Some years later, I would read Antonio Damasio's "Descartes' Error" who takes this argument a step further, and convincingly shows that our emotional brain ultimately produces rationality !)
To prove his point, Ronald de Sousa focuses on the way our emotions evolve during our lifetime. He starts his investigation with the way philosophy has treated emotions so far, trying to classify them, but without being able to come up with the definitive list. He then formulates the following hypothesis : "... yet it cannot be denied that there are, in other animals as in human babies, modes of behavior that we take to express something like human emotions. I think we can understand, in principle, how our repertoire of emotions gets built up, without positing a set of "primary emotions" that get combined like basic blocks or even mixed like primary colors. We do need a repertoire of primitive instinctual responses, but emotions are not mere responses. My hypothesis is this : We are made familiar with the vocabulary of emotion by association with paradigm scenarios. These are drawn first from our daily life as small children and later reinforced by the stories, art, and culture to which we are exposed. Later still, in literate cultures, they are supplemented and refined by literature. Paradigm scenarios involve two aspects : first, a situation type providing the characteristic objects of the specific emotion-type, and second, a set of characteristic or "normal" responses to the situation, where normality is first a biological matter and then very quickly becomes a cultural one."
What makes us human is the development of our emotions, not the capacity to do mental arithmetic or read a map. Our neocortex is an extension of our limbic system, our emotional brain. That explains also why all our actions are motivated by our emotions. Morality goes hand in hand with underlying emotions.
Now, the beauty of philosophy lies in the fact that de Sousa has been proven right by scientific investigation *afterwards*, confirming once again that philosophy is the mother of science. Helen Fisher would show in her book "Why we love", published in 2004, that when brain scans are performed on people that recently fell in love, compared to people who have a stable relationship for some years, there is a clear displacement of brain activity from the limbic system to the neocortex, from "being in love" as a primary emotion to "love" as a moral emotion.