How do you feel - and why?

The answer it gives to this troubling conundrum is that cruelty results from a lack of empathy. This is defined by Cambridge professor of developmental psychology Baron Cohen as the "ability to identify what someone else is thinking or feeling and to respond to their thoughts and feelings with an appropriate emotion".

Nazis could despatch Jews and yet be unable to hurt a fly

In turn, he claims lack of empathy is due to a malfunction in a part of the brain which he calls "the empathy circuit". When functioning normally, empathy results. When it functions abnormally, zero-empathy follows and then people can quite happily murder their own children.

A defective empathy circuit can be due, Baron Cohen says, to both genetic and environmental causes. Some people are born that way. In others, it results from how they were treated in infancy or childhood. Lack of sufficiently attentive parenting is, he claims, liable to impair development of the empathy circuit in ways that sometimes only become manifest in adulthood.

Baron Cohen's explanation of cruelty seems overly simple. It seemingly accords insufficient attention to how selective the lack of empathy often is in cruel people. A Nazi concentration guard could quite happily despatch a couple of Jews before breakfast and then go home to wife and child unable hurt a fly. Even Adolf Hitler was believed to be a moral vegetarian.

What needs explaining is how effortlessly many cruel people seem to turn off and on their empathy circuits at will. Until this accomplishment is explained, Baron Cohen's attempt to abandon good and evil for the bright morality-free uplands of neurology seems ill-fated.

For clues as to what may account for selectivity in the lack of empathy in so many cruel people, Baron Cohen might usefully have consulted Stephen Frosh's new book. Here, in writing about antisemitism, this fellow psychology professor - at Birkbeck College, London - quotes psychoanalyst Otto Fenichel: "the antisemite, immersed in confusion and led astray by ideological forces, sees in the Jew everything which brings him misery - not only his social oppressor but also his own unconscious instincts".

Reference to politically motivated false beliefs, and to the dynamics of the unconscious, seems a far more promising way in which to account for a lot of human cruelty than does a preoccupation with the hard-wiring of the brain.

It is the role of the unconscious in determining the vicissitudes of our inner emotional lives that forms the principal subject of Frosh's illuminating book. Chapters are devoted to each of the principal feelings that matter most to most people: their feelings of sadness, gladness, love, and hate.

It also discusses several other equally interesting questions, such as why we so frequently lose touch with our feelings and thereby cease feeling intensely about anything; why our lives are impoverished when that happens; and how, with the aid of psychoanalysis, we may be assisted in feeling better, in both the sense of feeling less miserable, as well as more closely connected with our feelings and able thereby to enjoy closer and more fulfilling relations with others.

While each book is written by a master of his discipline, it is Frosh's deceptively slim, but profound, volume that is the more convincing.

David Conway teaches philosophy at the University of Essex