Other philosophical questions are more theoretical, although they often arise through thinking about practical issues. The questions just listed, for example, may prompt more general philosophical questions about the circumstances under which it may be morally justifiable to take a life, or about the extent to which the state may restrict the liberty of the individual. Some "classic" questions of philosophy are speculative and theoretical and concern the nature of knowledge, reality and human existence: for example, "What, if anything, can be known with certainty?", "Is the mind essentially non-physical?", "Are values absolute or relative?", "Does the universe need explanation in terms of a Supreme Intelligence?", "What, if anything, is the meaning or purpose of human existence?" Finally, the philosophical questions are typically about conceptual issues; they are often questions about our concepts and the relation between our concepts and the world they represent. Every question implies a statement and every statement implies a question.