=Association of Ideas.= 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. In the case of the writer, the following words came to mind in the first few seconds: horse, bridle, saddle, tail, harness, buggy, whip, man, sky, stars, sun, ocean. Why did these words come, and why did they come in that order? Why did the idea "horse" suggest the idea "bridle"? And why did "bridle" suggest "saddle"? Is there something in the nature of ideas that couples them with certain other ideas and makes them _always_ suggest the other ideas? No, there is not. Ideas become coupled together in our experience, and the coupling is in accordance with our experience. Things that are together in our experience become coupled together as ideas. The idea "horse" may become coupled with any other idea. The general law of the association of ideas is this: Ideas are joined together in memory or revived experience as they were joined in the original or perceptive experience. But the matter is complicated by the fact that things are experienced in different connections in perceptive experience. I do not always experience "horse" together with "bridle." I sometimes see horses in a pasture eating clover. So, as far as this last experience is concerned, when I think "horse" I should also think "clover." I sometimes see a horse running when a train whistles, so "whistle" and "horse" should be coupled in my mind. A horse once kicked me on the shoulder, so "horse" and "shoulder" should be connected in my mind. And so they are. The very fact that these various experiences come back to me proves that they are connected in my mind in accordance with the original experiences. The revival of various horse experiences has come to me faster than I could write them down, and they are all bound together in my memory. If I should write them all out, it would take many hours, perhaps days.