After being adopted by Laws, however, the idea of fundamentalism spread beyond core doctrinal beliefs and became gradually identified with a set of attitudes about proper Christian behavior and thought—against drinking and dancing, against the teaching of evolution in schools. And so the term began to acquire its modern connotations of rigid orthodoxy.

In a presentation at the Aspen Ideas Festival, the author and religious scholar Karen Armstrong argued the word is too broadly applied. “It made perfect sense to the Americans in the 1920s when they coined the phrase,” Armstrong told me after her session had ended, “because they were going back to the ‘fundamentals’ of Christianity.” But when people talk about “fundamentalist Islam,” for example, Armstrong said, they’re connecting two ideas that fit poorly atop one another, and giving the false impression “that ‘fundamentalism’ is a monolithic movement throughout the world.”

Armstrong is joining a roiling, decades-long debate about how or whether the word should be applied outside of its original Protestant Christian origin. The late Hans Jansen, a Dutch scholar often critical of Islam, considered the debate long ended, as this acerbic passage from his 1997 book The Dual Nature of Islamic Fundamentalism indicates:

The late 1970s and the 1980s also saw an infertile discussion on the question whether it was proper to use the term ‘fundamentalism’ of developments taking place in the world of Islam. Was this term not much too simplistic to give adequate expression to such a complicated phenomenon? In a way the discussion on the word ‘fundamentalism’ echoes the discussion once caused by the invention of the telephone. Would not the term ‘telephone’ be much too simplistic? Would it do justice to the beauty and the many possibilities of the device? How about ‘speaking telegraph’ or ‘electrical speaking telephone’? Both Muslims and friends of the Islamic world feared that the word ‘fundamentalism’ had too much of a Christian flavour. Did it not stem from a North American Christian milieu, and was it not actually coined around 1920, and then by a journalist? Would not a term like ‘revolutionary extremist neotraditionalist ultra-Islamic radicalism’ be preferable?

Khalid Yahya Blankinship, a Muslim scholar of Islam, takes a different view in his book, Fundamentalism: Perspectives on a Contested History:

When the term ‘fundamentalism’ began to be applied to various trends among Muslims in the 1970s, it soon came into wide and somewhat indiscriminate use. But what exactly its users meant by the term and why especially they began to use it at that time have remained rather unclear. While at its origin in 1920, the term referred to a specific Christian movement and tendency in the United States, even being taken up by some as a self-identity, it also tended from the outset to be used to classify others rather than the self. After it began to be applied to non-Christians, especially Muslims, its coherence dwindled, as different commentators used it rather indiscriminately to refer to various tendencies and trends among Muslims. The result today has been a confusion of different definitions, often mutually exclusive or contradictory.

Even today’s Christians argue about the word’s usefulness. “‘Fundamentalist’ is a term that is frequently bandied about in the news media these days,” begins an essay by Larry Eskridge, a scholar of American religion at Wheaton College. “Casually invoked to describe anyone who seems to hold some sort of vaguely-perceived traditional religious belief—be they a Bible Baptist TV preacher, a Hasidic rabbi, a Mormon housewife, or a soldier of the Islamic Jihad—the word has become so overused as to be nearly useless.” This 2010 Reddit AMA from a self-proclaimed fundamentalist Christian sets the word in quotation marks. (I am a “fundamentalist” Christian. Ask me anything!)

But the notable thing about that Reddit thread is the author’s own definition of fundamentalism: “I mean that I believe in what I see as the ‘fundamentals’ of Christianity.” You may have to go to Reddit to find them, but someone, somewhere is using the word exactly as Curtis Lee Laws once intended.