One of Leo Strauss' most illuminating essays begins with a provocation: "A social science that cannot speak of tyranny with the same confidence with which medicine speaks, for example, of cancer, cannot understand social phenomena as what they are. It is therefore not scientific."

Something similar might be said about a religion columnist who finds it impossible to define religion.

I'm referring to The New York Times' Mark Oppenheimer, who penned a remarkable "Beliefs" column that ran on Saturday. The subject of the column? Whether CrossFit — a trendy form of demanding physical exercise — might be a form of religion. Oppenheimer's answer? Sure! Because "it's surprisingly hard to say what makes a religion."

Is it really?

The fact that Oppenheimer found a woman who really, really likes CrossFit and thinks about it "as others might speak about a church or synagogue community" doesn't prove that CrossFit really is her religion — any more than the fact that a couple of student researchers at Harvard Divinity School interviewed this same CrossFit fanatic for a study of "spaces other than churches that function as spiritual communities" demonstrates that a CrossFit gym is actually a place of religious worship.

Unless, of course, we define "religion" to mean "stuff someone really, really likes."

Which is pretty much how Oppenheimer defines religion. Sure, he talks to one scholar with a more rigorous definition — religion is an activity that "establishes a worldview" — but Oppenheimer is quick to assure us that this is "just one way of answering the question of what a religion is." And, apparently, not a very interesting way. Oppenheimer is much more intrigued by those Div School grad students who co-hosted a talk last month titled "CrossFit as Church?!" with none other than Greg Glassman, co-founder of… CrossFit.

Oh, I know what you're thinking: Of course the co-founder of CrossFit likes the idea of people joining (and paying for memberships in) the Church of The Company He Owns and Runs. But that doesn't stop Oppenheimer from devoting more space in the column to quoting Glassman's self-aggrandizing pseudo-spiritual gobbledygook than any other single source. (That includes religion scholars who are happy to proclaim football, Star Trek, and dieting fads forms of religion as well.)

In the end, Oppenheimer is content with suggesting that maybe "anything that creates community and engenders passionate devotion can constitute religion," even though that definition, he admits, has the result of draining the term of "all meaning." "If everything is religion," writes the man who makes a living writing about religion, "then maybe nothing is."

Unless I'm mistaken, Oppenheimer has just argued himself out of a job.

It may not bother Oppenheimer that he's defined religion away. But it should bother all of those who, you know, care about religion.

As someone in the latter category, allow me to give this definition thing a shot: Religion is any set of norms, practices, and beliefs that establishes a comprehensive way of life that is held out as the right or best way of life for those who adhere to it.

Many of these comprehensive ways of life posit the existence of one or more deities, but not all of them do — just as others teach that a life awaits us after death, while still others make no such claims. What matters is the comprehensiveness, not the content, of the way of life.

It is above all this comprehensiveness that precludes CrossFit from qualifying as a religion, even for those who take the fitness routine very seriously, because it is still just a form of physical exercise and not a sweeping statement of how a human being should live and understand his or her place in the universe. It makes no broader claims about the meaning or purpose of life, death, morality, love, and the origins, foundations, and ends of existence. The same holds for football, Star Trek, and dieting fads. Which is why those activities aren't religions but Judaism, Christianity, Islam, Mormonism, Hinduism, Buddhism, Shintoism, Taoism, Jainism, and Sikhism very clearly are.

This is also why the great rival to religion is philosophy, which likewise aims to provide comprehensive answers to life's biggest questions. (Unlike, say, organized sports, TV shows, or exercise regimens.)

The primary thing that separates religion and philosophy is a difference in their foundations and approach to seeking truth. Whereas religion is typically based on some form of revelation, mystical intuition, or extra-rational insight, a philosophical life is one lived in relentless pursuit of the comprehensive truth using reason or rational reflection alone.

These are, of course, ideal types. Some comprehensive views — neo-Platonism, Thomism, Confucianism, some forms of Buddhism — blend elements of religion and philosophy, revelation and reason. But in every case, the synthesis purports to grant comprehensive knowledge of the best way of life for a human being.

Not everyone has thought deeply about these matters. Raise the topic for discussion with your average person on the street — or in the pews, or at a CrossFit gym — and you're likely to hear some confused and confusing statements. That's hardly surprising.

After all, they're not paid to write about religion for The New York Times.