It is well known that the thought-form of an idea may be projected onto a blank paper, and there become visible to a hypnotised person. Or it may be made so objective that the hypnotised person will see and feel it as though it were an actual physical object. Many thought-forms exist, more or less permanently, of characters from history, drama, fiction, etc. Thus for example, popular fancy has strongly depicted characters and scenes from the plays of Shakespeare, from Bunyan’s Pilgrim’s Progress, from fairy stories such as Cinderella, Aladdin’s Lamp, etc. Such thought-forms are collective, having coalesced from the products of the imagination of countless individuals. Children have vivid and capable imaginations, so books read by them are usually well represented in the world of thought-forms, many excellent and life-like portraits existing of Sherlock Holmes, Captain Kettle, Dr. Nikola, and many others.
On the whole however, the thought-forms evoked from the novels of to-day are by no means as clear as those which our forefathers made of Robinson Crusoe or of the characters of Shakespeare’s plays. This of course, is because people today read more superficially and with less serious attention than was the case formerly. So much for the genesis of thought-forms. We pass now to consider their effects on their creators and on others.
Each man as he moves through life produces three classes of thought-forms:
 Those which, being neither centred round the thinker nor specially aimed at any person, are left behind him as a sort of trail which marks his route.
 Those, which being centred round the thinker, hover round him and follow him wherever he goes.
 Those which shoot straight out away from the thinker, aiming at a definite object.
A thought-form of Class I, being neither definitely personal nor specially aimed at someone else, simply floats detached in the atmosphere, all the time radiating vibrations similar to those originally sent forth by its creator. If the form does not come in contact with any other mental body the radiation gradually exhausts its store of energy, and in that case the form falls to pieces. But if it succeeds in awakening sympathetic vibrations in any mental body near at hand, an attraction is set up and the thought-form is usually absorbed by that mental body.
At the present stage of evolution the majority of the thoughts of men are usually self-centred even when they are not actively selfish. Such self-centred thoughts hang about the thinker. Most men, in fact, surround their mental bodies with a shell of such thoughts. They hover ceaselessly about them and constantly react on them. Their tendency is to reproduce themselves -i.e.,, to stir up in the man a repetition of the thoughts which he had previously entertained. Many a man feels this pressure upon him from within, this constant suggestion of certain thoughts, especially when he is resting after his labours, and there is no definite thought in his mind. If the thoughts are evil, he frequently thinks of them as tempting demons goading him into sin. Yet they are none the less entirely his own creation; he is his own tempter. Repeated thoughts of this kind play an important part in working out what is called Prarabda or “ripe” karma.
Persistent reiteration of thoughts of the same kind, say of revenge, bring a man at last to a point which may be compared to that of a saturated solution. Just as the addition of further matter of the same kind to the solution will produce the solidification of the whole, so will a slight additional impulse result in the commission of a crime. Similarly, reiterated thoughts of helping others may, when the stimulus of opportunity touches the man, crystallise out as an act of heroism.
Under such circumstances, a man may marvel at his own commission of a crime or at his own performance of some heroic act of self-sacrifice, not realising that repeated thought had made the action inevitable. A consideration of these facts goes far towards explaining the old problem of freewill and necessity or destiny. Furthermore, a man’s thought-forms tend to draw towards the man the thought-forms of others of a similar nature. A man may thus attract to himself large reinforcements of energy from outside; it lies within himself, of course, whether these forces that he draws into himself be of a good or evil kind.
***From Arthur E. Powell – The Mental Body