It has been argued that Spiritual Intelligence cannot be recognized as a form of intelligence. Howard Gardner, originator of multiple intelligence theory, chose not to include spiritual intelligence amongst his intelligences due to the challenge of codifying quantifiable scientific criteria.[3] Later, Gardner suggested an "existential intelligence" as viable, but argued that it was better to "put aside the term spiritual, with its manifest and problematic connotations, and to speak instead of an intelligence that explores the nature of existence in its multifarious guises. Thus, an explicit concern with spiritual or religious matters would be one variety—often the most important variety—of an existential intelligence." [4]