Different types exist among the Anabaptists, although the categorizations tend to vary with the scholar's viewpoint on origins. Estep claims that in order to understand Anabaptism, one must "distinguish between the Anabaptists, inspirationists, and rationalists". He classes the likes of Blaurock, Grebel, Balthasar Hubmaier, Manz, Marpeck, and Simons as Anabaptists. He groups Müntzer, Storch, et al. as inspirationists, and anti-trinitarians such as Michael Servetus, Juan de Valdés, Sebastian Castellio, and Faustus Socinus as rationalists. Mark S. Ritchie follows this line of thought, saying, "The Anabaptists were one of several branches of 'Radical' reformers (i.e. reformers that went further than the mainstream Reformers) to arise out of the Renaissance and Reformation. Two other branches were Spirituals or Inspirationists, who believed that they had received direct revelation from the Spirit, and rationalists or anti-Trinitarians, who rebelled against traditional Christian doctrine, like Michael Servetus."