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. Instead, Gardner suggested an "existential intelligence" as viable. However, contemporary researchers continue 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.
Variations of spiritual intelligence are sometimes used in corporate settings, as a means of motivating employees. and providing a non-religious, diversity-sensitive framework for addressing issues of values in the workplace. According to Stephen Covey, "Spiritual intelligence is the central and most fundamental of all the intelligences, because it becomes the source of guidance for the others."
Definitions of spiritual intelligence rely on the concept of spirituality as being distinct from religiosity.
Danah Zohar defined 12 principles underlying spiritual intelligence:
- Self-awareness: Knowing what I believe in and value, and what deeply motivates me.
- Spontaneity: Living in and being responsive to the moment.
- Being vision- and value-led: Acting from principles and deep beliefs, and living accordingly.
- Holism: Seeing larger patterns, relationships, and connections; having a sense of belonging.
- Compassion: Having the quality of "feeling-with" and deep empathy.
- Celebration of diversity: Valuing other people for their differences, not despite them.
- Field independence: Standing against the crowd and having one's own convictions.
- Humility: Having the sense of being a player in a larger drama, of one's true place in the world.
- Tendency to ask fundamental "Why?" questions: Needing to understand things and get to the bottom of them.
- Ability to reframe: Standing back from a situation or problem and seeing the bigger picture or wider context.
- Positive use of adversity: Learning and growing from mistakes, setbacks, and suffering.
- Sense of vocation: Feeling called upon to serve, to give something back.
Robert Emmons defines spiritual intelligence as "the adaptive use of spiritual information to facilitate everyday problem solving and goal attainment." He originally proposed 5 components of spiritual intelligence:
- The capacity to transcend the physical and material.
- The ability to experience heightened states of consciousness.
- The ability to sanctify everyday experience.
- The ability to utilize spiritual resources to solve problems.
- The capacity to be virtuous.
The fifth capacity was later removed due to its focus on human behavior rather than ability, thereby not meeting previously established scientific criteria for intelligence.
Frances Vaughan offers the following description: "Spiritual intelligence is concerned with the inner life of mind and spirit and its relationship to being in the world."
Cindy Wigglesworth defines spiritual intelligence as "the ability to act with wisdom and compassion, while maintaining inner and outer peace, regardless of the circumstances." She breaks down the competencies that comprise SQ into 21 skills, arranged into a four quadrant model similar to Daniel Goleman's widely used model of emotional intelligence or EQ. The four quadrants of spiritual intelligence are defined as:
- Higher Self / Ego self Awareness
- Universal Awareness
- Higher Self / Ego self Mastery
- Spiritual Presence / Social Mastery
David B. King has undertaken research on spiritual intelligence at Trent University in Peterborough, Ontario, Canada. King defines spiritual intelligence as a set of adaptive mental capacities based on non-material and transcendent aspects of reality, specifically those that:
"...contribute to the awareness, integration, and adaptive application of the nonmaterial and transcendent aspects of one's existence, leading to such outcomes as deep existential reflection, enhancement of meaning, recognition of a transcendent self, and mastery of spiritual states."
King further proposes four core abilities or capacities of spiritual intelligence:
- Critical Existential Thinking: The capacity to critically contemplate the nature of existence, reality, the universe, space, time, and other existential/metaphysical issues; also the capacity to contemplate non-existential issues in relation to one's existence (i.e., from an existential perspective).
- Personal Meaning Production: The ability to derive personal meaning and purpose from all physical and mental experiences, including the capacity to create and master a life purpose.
- Transcendental Awareness: The capacity to identify transcendent dimensions/patterns of the self (i.e., a transpersonal or transcendent self), of others, and of the physical world (e.g., nonmaterialism) during normal states of consciousness, accompanied by the capacity to identify their relationship to one's self and to the physical.
- Conscious State Expansion: The ability to enter and exit higher states of consciousness (e.g. pure consciousness, cosmic consciousness, unity, oneness) and other states of trance at one's own discretion (as in deep contemplation, meditation, prayer, etc.).
Also, Vineeth V. Kumar and Manju Mehta have also researched the concept, extensively. Operationalizing the construct, they defined spiritual intelligence as "the capacity of an individual to possess a socially relevant purpose in life by understanding 'self' and having a high degree of conscience, compassion and commitment to human values."
Measurement of spiritual intelligence relies on self-reporting. David King and Teresa L. DeCicco have developed a self-report measure, the Spiritual Intelligence Self-Report Inventory (SISRI-24) with psychometric and statistical support across two large university samples. Cindy Wigglesworth has developed the SQ21, a self-assessment inventory that has tested positively for criterion validity and construct validity in statistically significant samples. Wigglesworth's SQ model and assessment instrument have been successfully used in corporate settings.
The Scale for Spiritual Intelligence (SSI; Kumar & Mehta, 2011) is a 20-item, self-report measure of spiritual intelligence in adolescents. The idea behind the development of this scale was to generate and assess the concept of spiritual intelligence in the collectivist culture bounded with eastern philosophy. The SSI is rated on a Likert scale and can be completed in 10 minutes.
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. 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.” 
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- Zohar, D., ReWiring the Corporate Brain: Using the New Science to Rethink How We Structure and Lead Organizations (1997; ISBN 9971-5-1214-9)
- Gardner, Howard, A Case Against Spiritual Intelligence, The International Journal for the Psychology of Religion, Volume 10, Issue 1 January 2000, pp. 27-34
- Gardner, Howard, Intelligence reframed: multiple intelligences for the 21st century (Basic Books, 1999) p.53
- Hopelessly devoted | Money | The Guardian
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- Emmons, R.A. (2000). Is spirituality an intelligence? The International Journal for the Psychology of Religion. 10:27-34.
- Vaughan, F. What is Spiritual Intelligence? Journal of Humanistic Psychology, Vol 42, No. 2. Spring 2002, 16-33, 2003 Sage Publications.
- Wigglesworth, Cindy, "Why Spiritual Intelligence is Essential to Mature Leadership", Integral Leadership Review Volume VI, No. 3, August 2006
- "A Viable Model and Self-Report Measure of Spiritual Intelligence," David B. King & Teresa L. DeCicco (2009) The International Journal of Transpersonal Studies, Volume 28, pp. 68-85
- "A Viable Model and Self-Report Measure of Spiritual Intelligence", David B. King & Teresa L. DeCicco (2009) The International Journal of Transpersonal Studies, Volume 28, pp. 68-85
- Kumar, V.V., & Mehta, M.(2011). Gaining adaptive orientation through spiritual and emotional intelligence. In A.K.Chauhan & S.S.Nathawat (Eds.), New facets of positivism(pp 281-301).Delhi: Macmillan Publishers India.
- Wigglesworth, Cindy, SQ21: The 21 Skills of Spiritual Intelligence (New York: SelectBooks, 2012, p.189)
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- Kumar, V.V., & Mehta M.(2011).Scale for Spiritual Intelligence [Electronic Database]. Retrieved from PsycTESTS. doi:10.1037/t16725-000