When news breaks of a psychopathic crime, usually murder, people use a particular set of adjectives that reflect their horror, writes "Anatomy of Evil" author, psychiatrist Michael H. Stone, "words like 'fiendish,' 'revolting,' 'heinous' and (pretty regularly) 'inhuman.'

"This is how we distance ourselves from the acts in question, as if to say: 'No human could do these things.' "

Oxford neuroscientist Kathleen Taylor concurs. Her new book, "Cruelty: Human Evil and the Human Brain," examines the roots and forms of human cruelty. Taylor writes:

"Cruelty is as old as humankind, if not older. At its core lies unjustified voluntary behaviour which causes foreseeable suffering to an undeserving victim or victims. ... [I]ts aim is to make its targets suffer physically or psychologically."

Why does cruelty exist? It is comforting to consider brutality an aberration and decency the norm. But, as Taylor reminds us, "Moral judgements, paradoxically, have been used to justify extraordinary cruelty."

She also notes our morbid fascination with evil and cruelty. "Horrific assaults and ingeniously unpleasant murders are abundantly available in mainstream fiction," both in books and on screen.

If that perverse appeal extends to nonfiction, then these two are likely to succeed in the marketplace, but it will be well deserved. The books are thorough in their research and thought-provoking in their approach.

They are also remarkably complementary. Understanding any subject requires a combination of empirical evidence and theory. "Anatomy of Evil" is largely empirical in its approach, while "Cruelty" focuses on analysis.

However, Stone's empiricism occasionally reaches the point of annoyance. From his systematic study of hundreds of "true crime" books and magazine articles plus interviews with some of the perpetrators, Stone has developed a 22-point scale of evil.

That scale might represent a breakthrough for criminologists, but nonexpert readers will find the distinctions between its levels to be subjective, subtle and unenlightening.

They will probably view Stone's frequent allusions to the scale and his placement of various crimes on it as an attempt to sell his method over a competing product.

Fortunately, Stone also provides a much more interesting and useful set of measurement criteria covering personality traits, behavioral traits, experiences and genetic predispositions. His book consists largely of a litany of criminal acts. When his research sources are thin, his stories inspire readers to skim, but when he has actually interviewed the perpetrators, his writing becomes compelling.

Kathleen Taylor's "Cruelty" is concerned less with quantifying evil and more with putting it in the broader context of human behavior. She discusses in detail two key concepts that enable ordinary people to become extraordinarily cruel:

"Otherization," which transforms the victims into something subhuman in the perpetrators' eyes; and "world-shaping," the inclination to see the world according to one's beliefs, even when those beliefs conflict with sensory information or other knowledge.

Taylor systematically describes the way the brain processes information that leads to actions, the role of emotion, the development of a belief system and the progression from callousness to sadism. Then, in her closing chapter, she leaves the realm of analysis for speculation and, some might say, self-justification.

"The scientific study of cruelty has consequences for our everyday understanding of human harm-doing. If we can come to grasp why people commit atrocities, we may be able to prevent them -- that is the hope."

To most, Taylor's goal of prevention probably seems too ambitious. They will probably be more in tune with Stone's "Final Thoughts." It is rare that we can recognize a person's potential for evil and even rarer that we can prevent an initial evil act. But he notes that we can -- and must -- learn from the painful object lessons from real-world mistakes.

But Stone also adds a note of hope. "The system is not perfect," he writes. "We need to pay more attention to subtleties of personality, becoming more restrictive with the psychopathic killers and more liberal with the non-psychopathic prisoners who show genuine signs of remorse, reform, and redemption."