Howard Gardner, the originator of the theory of multiple intelligences, chose not to include spiritual intelligence amongst his "intelligences" due to the challenge of codifying quantifiable scientific criteria.[3] Instead, Gardner suggested an "existential intelligence" as viable.[4] However, contemporary researchers continue to explore the viability of Spiritual Intelligence (often abbreviated as "SQ") and to create tools for measuring and developing it. So far, measurement of spiritual intelligence has tended to rely on self-assessment instruments, which some claim can be susceptible to false reporting.