The word "Reformed" is confusing in that it can be used in different ways. At the broader level, "Reformed" refers to those denominations separated from the Lutheran (Protestant) churches of the Reformation. This began as early as 1529 when Zwingli disagreed with Luther on the Lord's Supper. Calvin then agreed with Zwingli and since he was more influential in his writings, churches which followed his theology were called Calvinistic (or Reformed) but did not take Calvin's name as the name of the denomination as Lutherans did. Thus Reformed denominations took on various names, some including the term "Reformed' in a narrower sense, such as the Reformed Church in America, the Gereformeerde Kerken in the Netherlands and the Reformierte Kirche in Germany. In Scotland, however, the Reformed or Calvinistic denomination called itself Presbyterian, after their polity of being ruled by elders or presbyters. So the Presbyterian theology is really Reformed, in the broader use of the term, but the Presbyterian denominations are separate from the Reformed denominations, in the narrower use of the term Reformed. Although the list of churches in this category is primarily Reformed in the narrower sense, the other subcategories use the term in the broader sense.
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