There is a spectrum of Evangelicalism, and not all Evangelicals will answer this question in the same way. There has been an acknowledged difference between Conservative Evangelicals and Open Evangelicals in recent years, and some would argue that they are both different from the kind of Evangelicalism that was found in Anglican churches until the 1950s.
Below are some definitions that have been attempted over the years. If you know of others, or want to add your own, use the box below.
Michael Lawson referred to David Bebbington’s definition, now widely used: evangelicalism is a form of Christianity that is CONVERSIONIST, ie believes that lives need to be changed; ACTIVIST, ie expresses the gospel in effort and service; BIBLICIST, ie has a particular regard for the Bible; and CRUCICENTRIST, ie lays stress on the sacrifice of Christ on the cross. Michael felt that the PRIORITY OF PREACHING should be added, and that some attempt should be made to explain that Evangelicals have a PARTICULAR WAY OF READING SCRIPTURE, in the light of what he called the meta-narrative, ie the doctrine of the divinity of Christ (if I have understood him correctly).
Jim Basinger suggested these four distinctives in an Episcopal Evangelical Journal article (vol II No 5): DOCTRINE OVER EXPERIENCE (what the Bible says is true trumps what ‘feels right’ or ‘what I think’); CENTRALITY OF PREACHING; and Holy Communion as a SACRAMENT ADMINISTERED TO MAN, NOT A SACRIFICE OFFERED TO GOD; and an evangelical view of the church as a body defined by its BELIEF AND LIFE, NOT ITS POLITY.
John Richardson makes an interesting point, after referring to the definitions put forward by Martyn Lloyd-Jones and John Stott: ‘The sheer fact that the question has been asked so often, and that answers by such erudite contributors have apparently failed to settle the issue, forces us to acknowledge that evangelicalism is not a set of commonly-held, narrowly-defined, doctrines’ (http://ugleyvicar.blogspot.com/2009/08/what-is-evangelical.html).
The ‘classical’ definition for Anglican Evangelicals is that of J. C. Ryle, Bishop of Liverpool from 1880–1900. Ryle’s definition, in an essay in his book Knots Untied, uses five headings: the absolute supremacy of Holy Scripture, the completeness of human sinfulness and corruption, the saving work and office of Christ, the inward work of the Holy Spirit in the heart, and the outward and visible work of the Holy Spirit in one’s life. For a full statement of his definition, click on the ‘Evangelicalism’ category in the right hand column.
It seems to me that the one thing common to every definition is a higher view of Scripture than is held by other Christian traditions, and I would use that as the single defining characteristic, since all the others flow from it (or are thought to), and the only differences between Evangelicals arise from a different understanding of what Scripture actually teaches. So I would define Evangelicalism as the belief that for Christians the Bible is THE FINAL AUTHORITY FOR ALL MATTERS OF CHRISTIAN FAITH, CHRISTIAN LIFE AND CHRISTIAN WORSHIP. But Anglo-Catholics, and even some liberals, might say the same; Michael is right that we need to point out that we read Scripture in a distinctive way.
Evangelicals have not historically given equal weight to Scripture, tradition and reason, for instance, but have shared Hooker’s view of their respective value: “Scripture with Christian men being received as the Word of God, that for which we have probable, yea, that which we have necessary reason for, yea, that which we see with our eyes, is not thought so sure as that which the Scripture of God teacheth…” (Laws II:7:5) and “what Scripture doth plainly deliver, to that the first place both of credit and obedience is due; the next whereunto is whatsoever any man can necessarily conclude by force of reason; after these the voice of the Church succeedeth” (Laws V:8:2, my emphasis).
Evangelicals also believe that ‘credit and obedience’ is only due to what we ‘necessarily conclude’ from the things that Scripture plainly delivers, not reason musing on things in general. The same applies to ‘tradition’, or the voice of the church: when we’re not sure what Scripture means by what it says, we listen to other Christians, and the judgement of the church in such cases does ‘over-rule all other inferior judgments whatsoever’ (to continue the Hooker quote above), but when we are sure what Scripture means, we maintain it even if the rest of the church contradicts this. This is what the Reformers called ‘private judgement’. No one needs an intermediary between himself and God’s word, and no one has the right to act as one. What the rest of the church believes about something when Scripture is silent, such as an ‘apostolic succession’ as essential for ministry, is not seen as having any authority, and must always remain optional.

August 16, 2010 at 3:07 am
Thanks, Phillip, for this very useful resource.
November 8, 2010 at 5:18 pm
A historian I know and respect, Dr. Charles Cashdollar, made a comment that surprised me. In otherwise positive review of Gillis Harp’s 2003 _Brahmin Prophet: Phillips Brooks and the Path of Liberal Protestantism_, he criticizes Harp for providing “evangelical ammunition for today’s partisan religious wars against moderate and liberal believers.” I would have preferred the phrase “information for today’s difficult discussions between moderate and liberal believers.” The implication of Dr. Cashdollar’s choice of words is that evangelicals have started something, rather than been put in the position of defending and explaining something. Comment?
November 8, 2010 at 9:56 pm
Sadly, there can be no doubt that Church Historians, most of whom have a faith and church loyalty of their own, are as likely as anyone else to exaggerate information that strengthens the case of their preferred cause, and to ignore information that undermines it. I don’t know Dr Cashdollar’s work, but it’s a safe bet he sees himself as a moderate liberal. Seeing the opposition as the innovators is frequently part of the behavior pattern.
A few good atheist historians, who have no personal interest in what the evidence shows, could be very useful.
March 24, 2011 at 10:58 am
Posted this elsewhere on Barnabas. Thought it was of interest.
“Jason Ingalls just posted a link to a blog for Evangelicals, many (maybe most?) not in “mainline churches,” although I’ll have to read it again to be sure. What I read of it was pretty interesting. Here’s the link: http://me.lt/9W7qa