Despite centuries of trying, the term 'religion' has proven impossible to define. Then why does it remain so necessary?

The Elusive Idea of Religion: Why a Slippery Word Still Shapes Our World. Imagine a word so familiar it seems woven into the fabric of human experience, yet so slippery that centuries of thinkers have failed to pin it down. That's the strange story of “religion.” While gods, temples, and rituals have existed for millennia, the concept of “religion” as we know it is surprisingly modern. In ancient Rome, for instance, religio meant scrupulous observance, not a separate sphere of life. Other cultures had their own terms for worship and custom, but none mapped neatly onto our idea of “religion.” Even early Christians didn't see themselves as followers of one “religion” among many—they believed they possessed the truth. The category of religion as a bounded, comparable system only started to crystallize in the 17th century, as Europe fractured into religious factions and encountered new worlds. Scholars began searching for Christian-like structures in other traditions: sacred texts, founders, and doctrines. Where these didn't exist, they were often invented or imposed. As academic study advanced, Buddhism became a test case—could a tradition without a god even count as a “religion”? The very act of classifying exposed the limits of definition. Great minds tried to draw the boundaries. John Stuart Mill, Emile Durkheim, Max Müller, and others each offered definitions—religion as belief in spiritual beings, a system of symbols, or collective ritual. Yet every definition either left out too much or swept in too much, failing to capture the wild diversity of human practice. Some traditions were all ritual and no creed, others intense in doctrine but lacking ritual, and some blurred the line between the natural and supernatural. By the 20th century, hope for a universal definition had faded. Some proposed the idea of “family resemblances”—traditions loosely connected like cousins, with no single trait shared by all. Others argued that the very concept of “religion” is a product of Western modernity, shaped by political and intellectual habits rather than any natural essence. But if “religion” is so hard to define, why does the word endure? Here, the story takes a fascinating turn. Words sometimes survive not because they're precise, but because they do work. “Religion” is a social kind—a label that both describes and shapes reality. Once the category exists, people and communities begin to see themselves through its lens. The word becomes a force, organizing laws, research, personal identity, and even the way individuals live and believe. In law and politics, religion remains essential for defining rights and freedoms. In scholarship, it directs inquiry. For believers, it names a space where meaning is forged and defended. Like a map—not the territory itself, but a tool for navigating it—the concept of religion endures because it helps us find our bearings. Even if the borders are blurred, the map is still indispensable. In the end, “religion” persists not because it's clear, but because it's necessary—a shared act of attention that helps us make sense of the world, even as its meaning forever slips through our fingers.