All original thinkers and investigators of the hidden side of nature whether materialists—those who find in matter “the promise and potency of all terrestrial life,” or spiritualists—that is, those who discover in spirit the source of all energy and of matter as well, were and are, properly, Theosophists. For to be one, one need not necessarily recognize the existence of any special God or a deity. One need but worship the spirit of living nature, and try to identify oneself with it. To revere that Presence, the invisible Cause, which is yet ever manifesting itself in its incessant results; the intangible, omnipotent, and omnipresent Proteus: indivisible in its Essence, and eluding form, yet appearing under all and every form; who is here and there, and everywhere and nowhere; is ALL, and NOTHING; ubiquitous yet one; the Essence filling, binding, bounding, containing everything, contained in all. It will, we think, be seen now, that whether classed as Theists, Pantheists or Atheists, such men are near kinsmen to the rest. Be what he may, once that a student abandons the old and trodden highway of routine, and enters upon the solitary path of independent thought—Godward—he is a Theosophist; an original thinker, a seeker after the eternal truth with “an inspiration of his own” to solve the universal problems.
— H. P. Blavatsky, from “What are the Theosophists?”