In the American Christian religious landscape one finds Catholics, mainline Protestant religious denominations, and the rest that one can describe as evangelicals and fundamentalists. While the Catholics form a distinct group, there is a great deal of overlap between the other three categories and it is not often easy to see what distinguishes them. In particular, people tend to use the words fundamentalists and evangelicals interchangeably.

John Green of the University of Akron describes four cardinal beliefs of evangelicals that distinguishes them from mainline Protestants:

One belief is that the Bible is inerrant. It was without error in all of its claims about the nature of the world and the nature of God. A second belief is that the only way to salvation is through belief in Jesus Christ. A third belief, and one that is most well known, is the idea that individuals must accept salvation for themselves. They must become converted. Sometimes that’s referred to as a born-again experience, sometimes a little different language. Then the fourth cardinal belief of evangelicals is the need to proselytize, or in their case, to spread the evangel, to evangelize.

Now different members of the evangelical community have slightly different takes on those four cardinal beliefs. But what distinguishes the evangelicals from other Protestants and other Christians is these four central beliefs that set them apart.

Mainline Protestant Christians on the other hand have a slightly looser set of beliefs.

Mainline Protestants have a different perspective. They have a more modernist theology. So, for instance, they would read the Bible, not as the inerrant word of God, but as a historical document, which has God’s word in it and a lot of very important truths, but that needs to be interpreted in every age by individuals of that time and that place.

Mainline Protestants tend to also believe that Jesus is the way to salvation. But many mainline Protestants would believe that perhaps there are other ways to salvation as well. People in other religious traditions, even outside of Christianity, may have access to God’s grace and to salvation as well, on their own terms, and through their own means.

Mainline Protestants are much less concerned with personal conversion. Although they do talk about spiritual transformation, they’ll often discuss a spiritual journey from one’s youth to old age, leading on into eternity. So there is a sense of transformation, but there isn’t that emphasis on conversion — on that one moment or series of moments in which one’s life is dramatically changed.

So mainline Protestants don’t discount conversion, but they simply don’t regard it as a central feature of their beliefs. Finally, mainline Protestants are somewhat less concerned with proselytizing than evangelicals. Certainly, proselytizing is something they believe in. They believe in sharing their beliefs with others, but not for the purposes of conversion necessarily. The idea of spreading the word in the mainline tradition is much broader than simply preaching the good news. It also involves economic development. It involves personal assistance, charity, a whole number of other activities.

Fundamentalists tend to have the most well defined belief structure as this article points out.

The first formulation of American fundamentalist beliefs can be traced to the Niagara Bible Conference and, in 1910, to the General Assembly of the Presbyterian Church which distilled these into what became known as the “five fundamentals”:

• The inspiration of the Bible by the Holy Spirit and the inerrancy of Scripture as a result of this.
• The virgin birth of Christ.
• The belief that Christ’s death was the atonement for sin.
• The bodily resurrection of Christ.
• The historical reality of Christ’s miracles.

By the late 1910s, theological conservatives rallying around the Five Fundamentals came to be known as “fundamentalists.”

Steve Waldman, editor-in chief of Beliefnet, said (back in 2003):

Evangelicals are a very broad group. It’s probably a third or 40 percent of the population of the United States. Fundamentalists are a subset of that. They are very conservative politically. Have a literalist view of the Bible.

Evangelicals have a much wider range of political views. A lot of them are conservatives, but not all of them. About a third of evangelicals voted for Al Gore. So it’s a pretty broad range.

And you tend to think of evangelicals as being fundamentalists because the most well known evangelicals are people like Jerry Falwell who are fundamentalists and are very conservative.

I am a little puzzled by the fundamentals. It would seem that if you believe in the first fundamental principle about the inerrancy of the Bible, then three of the other four fundamentals would follow as a direct consequence since they deal with supposedly factual events. Only the one about Jesus’s death being atonement for sin is doctrinal and would need to be separately spelled out. Perhaps the fundamentalists realized even back then that despite their followers’ claims to believe that the Bible was god’s inerrant word, very few people actually bothered to read it since the Bible is a big book and many Christians (as the Pew survey recently pointed out) have only the haziest of ideas of what it contains. So they emphasized those facts that their followers must be explicitly aware of and commit to.