Blackburn defines lust as "the enthusiastic desire, the desire that infuses the body, for sexual activity and its pleasures for their own sake." That definition is more sophisticated than may at first appear. Blackburn combines powerful concepts like enthusiasm, desire, sexual activity, and pleasure, but focuses his definition of lust on the desire for sexual pleasure for its own sake. This elevation of sexual desire, stripped of moral context and boundaries, well represents lust as it appears in our contemporary world.

The ancients identify the Seven Deadly Sins as pride, greed, lust, envy, gluttony, anger, and sloth. The entire panoply of human sinfulness was, they believed, traced to one of these root sins and the deadly effects that follow. The Christian church embraced the notion of the Seven Deadly Sins and joined them to the Seven Heavenly Virtues, identified as prudence, temperance, justice, fortitude, faith, hope, and charity. Presumably, temperance was designed to limit lust, but lust appears to have gained the upper hand.

Tracing the idea of lust through Western thought, Blackburn rejects the common association of lust with excess. Lust is not really about excessive desire, argues Blackburn, but rather a desire for sexual pleasure as an end in itself. Lust met disaster in the form of the Stoics who feared a life ruled by passion rather then reason. The Roman philosopher Seneca popularized a Stoic philosophy in adopting his motto as "nothing for pleasure's sake."

Seneca argued that lust was to be overcome for the survival of humanity, even as sexual was to be directed only toward "the continuation of the human race."  Of course, Seneca made this argument about lust in a letter he wrote to his mother, so it is difficult to know how seriously to take his description. Nevertheless, Blackburn takes him at his word.

But if the Stoics represented a significant setback for lust, this deadly sin met its deadliest opponent in Christianity. Blackburn describes this as "the Christian panic" that directed moral scrutiny to sexual pleasure itself, not just to what might be considered "excess."

Predictably, Blackburn directs his attention to Augustine, the fourth-century bishop whose views on sex have influenced at least fifteen centuries of Christian thought. Augustine, whose youth had been given to sexual excess, was, after his conversion, determined to deny that sexual pleasure was a part of the Creator's design for human sexuality, even from the beginning. Had the Fall not occurred, Augustine argued, sex would be a purely rational affair, untainted by any physical pleasure. Copulation would be, in effect, just like shaking hands.

Later, as represented in the thought of Thomas Aquinas, the Church argued that sexuality was defined both by Scriptural command and the revelation found in nature. This additional dimension of lust was directed at the "unnatural" desires evident in much of humanity.