The three gunas — the 'modes of nature' at the heart of Samkhya philosophy and the Bhagavad Gita. Indian thought holds that everything in nature, including each person's temperament, is woven from three strands: sattva (clarity, calm and harmony), rajas (drive, passion and restless motion) and tamas (stability, rest and inertia). All three live in everyone, but one tends to lead — colouring how you think, act, eat and feel. Modern psychology has turned this ancient map into validated questionnaires such as the Vedic Personality Inventory and the Mysore Triguna Scale; this asks which mode is strongest in you.
The three gunas (sattva, rajas, tamas) come from Samkhya philosophy and the Bhagavad Gita (chapters 14, 17-18). Modern psychologists have operationalised the model into validated self-report instruments — the Vedic Personality Inventory (Wolf, 1998; reported Cronbach's alpha approx .85-.92) and the Mysore Triguna Scale (Shilpa & Venkatesha Murthy, 2012). This is a reflective self-ID of which mode tends to lead in you, not a clinical or fixed measure: classically all three are present in everyone and shift over time. (The three gunas of Samkhya philosophy and the Bhagavad Gita; operationalised as the Vedic Personality Inventory (Wolf, 1998) and the Mysore Triguna Scale (Shilpa & Venkatesha Murthy, 2012))