<P> The Fourteenth Amendment to the United States Constitution (Amendment XIV) is one of the post-Civil War amendments, intended to secure rights for former slaves . It includes the due process and equal protection clauses among others . The amendment introduces the concept of incorporation of all relevant federal rights against the states . While it has not been fully implemented, the doctrine of incorporation has been used to ensure, through the Due Process Clause and Privileges and Immunities Clause, the application of most of the rights enumerated in the Bill of Rights to the states . </P> <P> The incorporation of the First Amendment establishment clause in the landmark case of Everson v. Board of Education has affected the subsequent interpretation of the separation of church and state in regard to the state governments . Although upholding the state law in that case, which provided for public busing to private religious schools, the Supreme Court held that the First Amendment establishment clause was fully applicable to the state governments . A more recent case involving the application of this principle against the states was Board of Education of Kiryas Joel Village School District v. Grumet (1994). </P> <P> Jefferson's concept of "separation of church and state" first became a part of Establishment Clause jurisprudence in Reynolds v. U.S., 98 U.S. 145 (1878). In that case, the court examined the history of religious liberty in the US, determining that while the constitution guarantees religious freedom, "The word' religion' is not defined in the Constitution . We must go elsewhere, therefore, to ascertain its meaning, and nowhere more appropriately, we think, than to the history of the times in the midst of which the provision was adopted ." The court found that the leaders in advocating and formulating the constitutional guarantee of religious liberty were James Madison and Thomas Jefferson . Quoting the "separation" paragraph from Jefferson's letter to the Danbury Baptists, the court concluded that, "coming as this does from an acknowledged leader of the advocates of the measure, it may be accepted almost as an authoritative declaration of the scope and effect of the amendment thus secured ." </P> <P> The centrality of the "separation" concept to the Religion Clauses of the Constitution was made explicit in Everson v. Board of Education, 330 U.S. 1 (1947), a case dealing with a New Jersey law that allowed government funds to pay for transportation of students to both public and Catholic schools . This was the first case in which the court applied the Establishment Clause to the laws of a state, having interpreted the due process clause of the Fourteenth Amendment as applying the Bill of Rights to the states as well as the federal legislature . Citing Jefferson, the court concluded that "The First Amendment has erected a wall between church and state . That wall must be kept high and impregnable . We could not approve the slightest breach ." </P>

Who is noted for advocating separation of church and state