"2. Concentration, or Yoga, is the hindering of the modifications of the thinking principle. In other words, the want of concentration of thought is due to the fact that the mind — here called "the thinking principle" — is subject to constant modifications by reason of its being diffused over a multiplicity of subjects. So "concentration" is equivalent to the correction of a tendency to diffuseness, and to the obtaining of what the Hindus call "one-pointedness," or the power to apply the mind, at any moment, to the consideration of a single point of thought, to the exclusion of all else... Upon this Aphorism the method of the system hinges. The reason for the absence of concentration at any time is, that the mind is modified by every subject and object that comes before it; it is, as it were, transformed into that subject or object. The mind, therefore, is not the supreme or highest power; it is only a function, an instrument with which the soul works... (Book I, Concentration)"