'The foregoing caveat about the real but metaphoric nature of clairvoyant descriptions extends also the proposition that thoughts are things. They are obviously not physical things, but rather energy complexes on the subtle level of reality that are analogous to physical things.
Thoughts forms are produced in our emotional or mental bodies and sent out from us into the mental atmosphere, where they are attracted to any other person with an aura whose vibrations are sympathic to theirs. Thought forms are thus a way of explaining what thoughts are.'

Annie Besant & Charles W. Leadbeater, Thought forms, Theosophical Publishing House, Adyar, Chennai, India, 1999