A flight of ideas is an abnormal rapidity of the stream of thought.
Every perception so immediately is linked with some association of experience that expression is swift and often incoherent. One word will follow another with amazing rapidity, words suggested by sound association, usually, rather than by that of meaning.
Example: “Made a rhyme, had a dime, did a crime, got the time, bring some lime.” This association by rhyme is quite common. But the associations of meaning are not uncommon.
Example: “Made a rhyme. Mary was a poet. Mary had a little lamb. Where’s Mary?—Mary!—No Jim—Jim, all my children—calling, calling, calling,” etc.
A fixed idea is one which morbidly stays in the mind and cannot be changed by reason.
Example: In hypochondriasis, as given above.
Ideogenous pains are either pains born of an erroneous idea, or mental reproductions of pains now having no physical cause.
A suggestible person, learning that his grandfather died of an organic heart, conceives the idea that he has inherited the trouble, and begins to suffer cardiac pains; and as long as the idea persists the pain is felt.
Compulsive ideas are ideas which intrude, recur, and persist despite reason and will.
Example: The compulsive idea of contamination may lead its victim to wash and rewash his hands at every contact with matter, until finally, though they are raw and sore, he is incapable of resisting the act.