I've often been asked, "How can the Church know what is true and not true? How can you say something is 'orthodox' and something is less than orthodox or simply not true at all?" We use the term 'mere Christianity' to delineate what doctrines are central to the proper definition of Christianity. But how do we know, for example, that JW and Mormon theology is to be qualitatively distinguished from orthodox Christianity?
The answer lies in The Weselyan Quadrilateral. The Wesleyan Quadrilateral“regards proper Christian belief as shaped by four main sources and norms: Scripture, Tradition, Reason and Experience,” (R. Olson, The Mosaic of Christian Belief, loc 638) with scripture as the foundation upon which the other three are based. For my Calvinist or non-Arminian friends, it should be noted that the tenets of the WQ goes back further than John Wesley–-they go back to the early church. When one asks, ‘How do you know that is true?’ one responds essentially with what is in line with the WQ.
Scripture – The canon that we find in our Bibles is the ultimate source and foundation for all belief. It is the spirit of the WQ and it is the final source of our theology. Any tradition, reason, and experience that may follow must be consistent with scripture, though they must be carefully considered in our interpretation of scripture.
Tradition – The Great Tradition, to use Olson's terminology, is essentially the church consensus of fundamental and foundational belief through the centuries. It is the fundamental ideas and doctrines which the Church has held onto since the origins and development of Christianity.
Reason – God does not ask us to commit to doctrines and beliefs blindly. In fact, without reason we are more likely to embrace unbiblical ideas. Reason is part of God’s essence (ho logos, Word, Logic, Order, etc) and thus it is a source for knowing and discerning truth.
Experience – What sort of transformation and revelation have we received in our own lives? What sort of experiences validate God's truth for us? We must be cautious simply for the fact that non-scriptural experience can be convincing. Certainly, taken alone, experience can lead us astray! But a full reliance on scripture-based experience may help us discover truth.
Obviously, with the WQ, a certain presuppositional acceptance must be made. One must acknowledge the authority and supremacy of God and the authority and inspiration of scripture. One must be willing to accept scripture as the foundation. There's no sufficient or practical way to argue the WQ with non-believers, expecting that such an answer will be satisfying. But as Christians, and within the Christian paradigm of thought, it is by Scripture, Tradition, Reason, and Experience that we judge what is true, what is in the free reign of discussion, and what is adamantly not true Christian doctrine.