Looking for Spinoza: joy, sorrow and the feeling brain by Antonio Damasio

Antonio Damasio made his name by explaining that our emotions are good for us. You might think you would be better off without any emotions, like Mr Spock in the original Star Trek, deciding every issue by logic alone. But a decade ago Damasio's bestseller Descartes' Error showed that this would be a disaster. Without any emotional reactions, you wouldn't know what to do. Logic might tell you what will follow from different actions, but you need your emotions to make you care about the consequences.

Descartes' Error sold half-a-million copies in over 20 languages, which is not bad for a professor of neurology at the University of Iowa writing about his specialist subject. The error in question was Descartes's view that emotions disrupt the proper working of the rational mind.

However, the book's real selling point was not the philosophical background to the argument, but Damasio's wide knowledge of the weird ways in which brain damage can alter behaviour. Among the characters he portrayed was Phineas Gage, the 19th-century Vermont railway worker who blasted a tamping iron through a good chunk of his brain. Amazingly, Gage survived the accident, but his emotional reactions did not, and he spent the rest of his life as a wastrel drifting from job to job. Even more tellingly, Damasio described how his stroke patient, code-named Elliott, would spend up to an hour debating the pros and cons of Wednesday versus Thursday for his next appointment, without getting any closer to a decision.

Damasio's new book has another 17th-century philosopher in the title, and is again concerned with the emotions. This time he wants to explain the relationship between emotions and feelings. You might think there isn't much of a difference here. But Damasio argues that emotional reactions are much more basic than conscious feelings.

Emotions are simple survival reflexes designed to deal with changing environments, and are found throughout the animal kingdom, even in such limited intellects as snails, flies or the single-celled paramecia who flee from high temperatures or sharp objects.

Conscious feelings, by contrast, require fancy brains to construct complex maps of the internal states of our bodies, thereby enabling us to monitor our current bodily well-being. It is these body-sensing feelings, rather than the more basic emotions, that Damasio now takes to play the crucial role in decision-making. We are moved by our awareness of our own bodily states, because we have been designed by evolution to look after our bodies.

What does all this have to do with Spinoza? Not a lot, to be honest. Damasio presents some of the Dutch philosopher's pronouncements about human nature as precursors of his own views, but has trouble getting round the fact that Spinoza had no inkling of the neuroscientific evidence on which Damasio bases his claims.

Because of this, Spinoza the man ends up figuring rather more prominently than Spinoza the thinker. Damasio speculates at length about the "abominable heresies" and "other enormities" that led to the young philosopher's excommunication from the Amsterdam synagogue, and wonders whether he found contentment in his banishment.

Sometimes, it seems as if there is another book struggling to emerge from this volume, like one of those novels in which a historical researcher finds that the subject's life is running parallel to their own. For example, Damasio asks how Spinoza would have turned out had his parents remained in Portugal, where Damasio himself grew up, and concludes that Spinoza would not have flourished under the restrictions of the old country. But this theme remains undeveloped, and Damasio soon turns back to his analysis of feelings.

Is he right to maintain that all feelings are representations of bodily states? When I am pleased by my child's success, or distressed at the death of a loved one, surely my feelings are about other people, not about my own body.

Damasio allows that this is in a sense true, but counters that we have these other-directed feelings only because other people sometimes matter to our own bodily well-being. In evolutionary terms, he argues, bodily survival is the bottom line, and so the feelings that motivate us must be telling us about our own bodily states.

However, this evolutionary logic can as easily be turned on its head. If we are talking evolution, the real bottom line is surely procreation, not survival. Our bodily well-being matters biologically only insofar as it helps us to produce and nurture our children. But many other external factors also matter to their welfare, like food, clothing, and places in desirable schools. So, if evolution fixes what we have feelings about, we should expect to care about these external things just as much as about our bodies. Come to think of it, if Damasio's body-centred view were right, it would be a mystery why we should ever bother with the awkward and unhygienic activities needed to conceive children in the first place (not to mention all those expensive dinners), given that we can produce just the same effects on our own bodies in a solitary manner.

Still, even if its central thesis is flawed, there remains much in this book to please Damasio's fans. He is a lively and humane writer, and ranges easily across a wide variety of topics, from Rembrandt's paintings and Shakespearean plays to the foundations of ethics and the nature of consciousness. Looking for Spinoza may not quite have the punch of Descartes' Error. But that was a hard act to follow, and this is a fine book all the same.

David Papineau is professor of philosophy at King's College London