I have enrolled in "The History of Christianity" at a college here in St. Louis. The teacher of the class is what I consider to be closed-minded and bigotted on the subject of what the definition of Christianity is.  His definition is tied directly to that of the Trinity and the Catholic church's definition of it and belief in Jesus Christ is not sufficient to call one's self a Christian.  While his saying it doesn't make it so,  I nevertheless feel insulted (or am I just neurotic? :^) ). I would like to be able to respond to him with some sense of literacy while maintaining an amiable student-teacher relationship.  So, is there common definition of what Christianity is?  As the previous discussion of the Trinity did not lend itself to an exchange of flames, I am hopeful that this will also not produce major flames.  Regards, -- Larry Autry Silicon Graphics, St. Louis autry@sgi.com     [Often we get into discussions about who is Christian.  Unfortunately there are a number of possible definitions.  Starting from the  broadest, commonly used definitions are:    a historical definition   people who accept Christ as Lord and savior   a broad doctrinal definition   narrow doctrinal definitions  1) By a historical definition I mean the sort of definition a secular historian would likely use.  This would include any group that developed out of the Christian church, and continues within the same broad culture.  E.g. some Unitarians would fail just about any doctrinal test you could come up with.  Yet it's clear that that group developed from Christianity, and people from very different backgrounds (e.g. Hindus) would likely see them as part of Christianity.  This is not a definition most Christians like, but it's relevant in some political and ethnic contexts.  2) Accepting Christ as Lord and savior is a test used by many Christian groups for membership, e.g. the Southern Baptists and Presbyterian Church (USA).  I would qualify it by saying that what most people have in mind is an exclusive commitment to Christ, so that someone who accepted Christ as one of many gods would not fit.  It's an attempt to formulate a criterion that is religious but is not based on technical doctrine.  By this definition, groups such as Arians would be viewed as heretical Christians, but still Christians.  In the modern context this would include Mormons, JW's, and "oneness Pentecostals".  They would be viewed as heretical Christians, but still Christian.  In practice I believe just about everyone who falls into this category would accept the Apostle's Creed.  3) The next level is an attempt to give a broad doctrinal definition, which includes all of the major strands of Christianity, but excludes groups that are felt to be outside "historic Christianity."  This is of course a slippery enterprise, since Catholics could argue that Protestants are outside historic Christianity, etc.  But I think the most commonly accepted definition would be based on something like the Nicene Creed and the Formula of Chalcedon.  The attempt is to characterize doctrines that all major strands of Christianity agree are key.  Obviously this is to some extent a matter of judgement.  A Mormon will regard the LDS church as a major strand, and thus will not want to include anything that contradicts their beliefs.  But I think this definition would have fairly broad acceptance.  4) Finally, some people use definitions that I would say are limited to a specific Christian tradition.  E.g. some evangelicals only consider someone Christian if he has had an evangelical-style conversion experience, and some I've even heard of groups that limit it to their specific church.  I think you can find contexts where each of these definitions is used. A lot is going to depend upon the purpose you're using it for.  If you're using it descriptively, e.g. in history or anthropology, you'll probably use definition 1 or 2.  If you're using it normatively, i.e. to say what you believe the Christian message is, you'll probably use a definition like 3 or even 4.