 Using thought experiments often employs an appearance principle. One version of an appearance principle is that a person has a reason for believing that some state of affairs (SOA) is possible if she can conceive, describe or imagine the SOA obtaining and she knows of no independent reasons for believing the SOA is impossible. As stated the principle is advanced as simply offering a reason for believing the SOA to be possible, and it thus may be seen a advancing a prima facie reason. But it might be seen as a secundum facie reason insofar as the person carefully scrutinizes the SOA and its possible defeaters (see Taliaferro &amp; Knuths 2017). Some philosophers are skeptical of appealing to thought experiments (see Van Inwagen 1998; for a defense see Taliaferro 2002, Kwan 2013, and Swinburne 1979; for general treatments see Sorensen 1992 and Gendler &amp; Hawthorne 2002).