Over the years, three different approaches have been developed for grounding originalism.
1. The first approach involves a normative argument for originalism. Under this approach, one argues that originalism is the normatively best way to interpret the Constitution. There are various versions of this approach. Justice Scalia argues that only originalism leads to clear rules to guide judges and the public. Judge Bork contended that originalism is the only approach compatible with democracy. Keith Whittington maintains that originalism is justified by popular sovereignty.
2. The second approach is an interpretive argument for originalism. Under this approach, one argues that the actual meaning of the document that is the Constitution is the original meaning. To determine the actual meaning, one must give it the meaning it would have had at the time of its enactment. This approach is adopted by both original public meaning advocates, such as Gary Lawson, and original intent defenders, such as Larry Alexander.
My own approach (with John McGinnis) makes both kinds of arguments. We argue originalism is the normatively best way of interpreting a good constitution and there is a strong reason to believe that a constitution enacted pursuant to strict supermajority rules will be a good one. We also argue the actual meaning is best determined through original methods originalism, which interprets the meaning of the Constitution based on the interpretive rules that would have been deemed applicable to the Constitution at the time of its enactment.