Thought is as much a thing as the yonder piece of stone. It has weight, colour, shape, size and form. Thought is a dynamic force. It is caused by the vibrations of psychic prar:a (sukðma prana) on the mental substance. It is a force like gravitation, cohesion or repulsion. Thought travels or moves. Thought has got tremendous power. Thought can heal diseases. Thoughts can transform the mentality of persons. Thought can do anything. It can work wonders. The velocity of thought is unimaginable.
Thought is a finer force. This is supplied to us by food. If you read Chandogya Upanishad – the dialogue between Uddalaka and Swetaketu – you will understand this point well. If the food is pure, thought also becomes pure. He who has pure thoughts speaks very powerfully and produces deep impression on the minds of the hearers by his speech. He influences thousands of persons through his pure thoughts. A pure thought is sharper than the edge of a razor. Entertain always pure sublime thoughts. Thought-culture is an exact science.
Thinking is of four kinds, viz., symbolic thinking, instinctive thinking, impulsive thinking and habitual thinking. Thinking through words is symbolic thinking. Instincts are more powerful than impulses. Thoughts of body, food, drink, bath, etc., are habitual thinking. You can stop easily symbolic thinking. It is difficult to stop instinctive and impulsive thinking.
Thought is a great force. Thought has tremendous power. It can be transmitted from one man to another man. You can move the world through thought-force. The powerful thoughts of great sages (rðis) of yore are still recorded in the akasa (akasic records). Yogis who have clairvoyant vision can perceive those thought-images. They can read them. You are surrounded by an ocean of thought. You are floating in the ocean of thought. You are absorbing certain thoughts and repelling some in the thought-world.
Every one has his own thought-world. Through practice of yama, niyama, pranayama and meditation, you can change impure thoughts into suitable pure thoughts. Meditation fills the mind with cheerful, powerful, satvic thoughts.