The word quadrilateral does not appear in John Wesley's own writing. It was coined in the twentieth century by a Methodist scholar studying Wesley's sermons and letters, who noticed the same fourfold pattern, scripture read through tradition, reason and experience, recurring across decades of Wesley's theological argument, and gave it a name Wesley himself never needed. The label caught on quickly inside Methodism, partly because it gave later Methodist theology a compact answer to a question every tradition has to face, on what basis a disputed doctrine gets decided, and partly because it distinguished Methodist method from both a strict biblicism that treats reason and experience with suspicion and a high church appeal to tradition as an authority standing beside scripture rather than beneath it.
The label has also drawn criticism from within Methodism, precisely because equal is not what Wesley meant and equal is what quadrilateral can suggest to a reader meeting the term for the first time. The Book of Discipline of the United Methodist Church addresses this directly in its statement of the church's theological task, describing scripture as the primary source and criterion of Christian doctrine while naming tradition, reason and experience as the lenses through which scripture is read, not as four independent pillars holding up the same roof.