adult while the engineer aged minimally, or the more overt intra-familial incest in To Sail Beyond the Sunset and Farnham's Freehold. Heinlein often posed situations where the nominal purpose of sexual taboos was irrelevant to a particular situation, due to future advances in technology. For example, in Time Enough for Love Heinlein describes a brother and sister (Joe and Llita) who were mirror twins, being complementary diploids with entirely disjoint genomes, and thus not at increased risk for unfavorable gene duplication due to consanguinity. In this instance, Llita and Joe were props used to explore the concept of incest, where the usual objection to incest—heightened risk of genetic defect in their children—was not a consideration. Peers such as L. Sprague de Camp and Damon Knight have commented critically on Heinlein's portrayal of incest and pedophilia in a lighthearted and even approving manner. Diane Parkin-Speer suggests that Heinlein's intent seems more to provoke the reader and to question sexual norms than to promote any particular sexual agenda. Philosophy In To Sail Beyond the Sunset, Heinlein has the main character, Maureen, state that the purpose of metaphysics is to ask questions: "Why are we here?" "Where are we going after we die?" (and so on); and that you are not allowed to answer the questions. Asking the questions is the point of metaphysics, but answering them is not, because once you answer this kind of question, you cross the line into religion. Maureen does not state a reason for this; she simply remarks that such questions are "beautiful" but lack answers. Maureen's son/lover Lazarus Long makes a related remark in Time Enough for Love. In order for us to answer the "big questions" about the universe, Lazarus states at one point, it would be necessary to stand outside the universe. During the 1930s and 1940s, Heinlein was deeply interested in Alfred Korzybski's general semantics and attended a number of seminars on the subject. His views on epistemology seem to have flowed from that interest, and his fictional characters continue to express Korzybskian views to the very end of his writing career. Many of his stories, such as Gulf, If This Goes On—, and Stranger in a Strange Land, depend strongly on the premise, related to the well-known Sapir–Whorf hypothesis, that by using a correctly designed language, one can change or improve oneself mentally, or even realize untapped potential (as in the case