The subject of the association of ideas can best be introduced by an experiment. Take a paper and pencil, and think of the word “horse.” Write this word down, and then write down other words that come to mind. Write them in the order in which they come to mind. Do this for three or four minutes, and try the experiment several times, beginning with a different word each time. Make a study of the lists of words. Compare the different lists and the lists written by different students.