Next time you drive down a street and look at the houses side-by-side, think of the Church's teaching that the family is the basic cell of society. Picture the walls of the houses as like the membranes of cells, and think of the life within those walls as either healthy or sick. The welfare of our society is constituted by the welfare of those "cells."

A 19th century German doctor named Rudolf Virchow became famous for arguing that all human diseases were diseases of cells, a revolutionary thought then. "Think microscopically!" he used to tell his students. Similarly nothing strikes at society except through striking at families. "Think households!" one might say now.

Some attacks weaken or kill a family's members from without -- war, plagues, economic crises. But the most serious woes are moral and undermine it from within, by subverting the family's structure, love, and habits. Of the many such inner threats today, pornography is among the most serious. It threatens to render all of society "sickened" from a moral point of view.

Pornography ought to be defined as any representation of human sexuality appealing to the imagination and in some manner promoting "porneia," sexual immorality -- that is, the satisfaction of sexual desire outside of a chaste marital embrace.

Pornography so defined includes, for instance, the Sports Illustrated Swimsuit edition; the difference between that and "hardcore" porn is a matter of degree. If a line is to be drawn to exclude all pornography, it needs to be drawn widely, which is why many do not wish to draw lines.

All pornography degrades, that is, it involves handing over the reins of our soul to some lower element in us, bringing us to down "to the level of an animal," but with this difference --degradation always includes some element of perversion of the higher element, which is something never seen among animals. The degree of degradation increases with the degree of pornography.

Similarly, all pornography involves a loss of freedom. In a vicious cycle, each repeated use renders us less free to say "no" to the next. The greater the degree of pornography, the greater the bondage.

Use of pornography unsettles someone's character in general. It leads to the development of other vices, such as wasting time, wasting money, and not keeping one's commitments. To be preoccupied with images and fantasies is a waste of life anyway.

Likewise pornography blocks us from good things. A habitual pornography user makes himself incapable of taking joy in others. Because only extreme experiences please him, he can no longer take pleasure in simple goods in life. His self-absorption and narcissism -- which he is blind to -- make him nearly incapable of love and even attraction, as, for instance, he won't be able to find his wife attractive.

A pornography user recognizes he has become in a real sense capable of outrages that previously would never have occurred to him. He is sometimes shocked by the badness he sees arising spontaneously from within him. He has enlivened the potential within him for serious crime.

The great Catholic novelist Walker Percy used to express astonishment at the "florid" outbreak of pornography in U.S. society in the early 1970s, as for example in the movie "Deep Throat" being shown in local theaters. The internet has recently proved a great engine of pornography, making even the most outrageous images available at a click of a mouse -- or by typing a word (sometime accidentally typed). The promotion of oral sex by Planned Parenthood and role models such at President Clinton has also played a part.

Pornography has become normalized. Its influence is discernible throughout popular culture, whose icons seem to have concluded that nothing without a pornographic edge will sell.

What caused this "florid outbreak"? Surely artificial contraception, which subverts the marital embrace, turning it into mere eroticism. If married couples, who have both the "office" and "responsibility" of articulating for society the meaning of sexual intercourse happily accept its perversion into eroticism, then who can be surprised if all of society follows suit? The relevant authorities have abdicated their responsibility; moral chaos follows.

What to do about the problem? Recognize its seriousness and insist on the need for "conversion," away from this sin and toward what used to be called, quaintly, "purity."

Remember the health analogy: Resistance to a disease is a matter of both strong immunity (general healthiness) and good hygiene (avoiding exposure). The best immunity is to practice viewing others as whole persons. A man should view each woman as he would view his sister or daughter. He should view himself as someone whose body is "for the Lord" (as St. Paul says) and meant to be used to show genuine love to others, not abused for self-satisfaction.

Of course "viewing" oneself and others in this way is not a matter of an intellectual trick but of acquiring virtues, which requires time, effort, and lots of grace.

Acquire self-knowledge. Practice prudent self-management, by installing filters and using computers in public places, and so on. Have frequent recourse to the graces of the Sacrament of Penance. Begin again if you fall. And ask the help of Mary, that lady of fairest love, who will always help you.

Michael Pakaluk is Professor of Philosophy at Ave Maria University. His book about his late wife and local pro-life activist, Ruth Pakaluk, called "The Appalling Strangeness of the Mercy of God," has just been published by Ignatius Press.