Images may be classified according to the material dealt with into object images or concrete images and into word or abstract images.  No one of these terms is very good as a name of the image referred to.  The first group—­object or concrete image—­refers to an image in which the sensory qualities, such as color, size, rhythm, sweetness, harmony, etc., are present.  The images of a friend, of a text-book, of the national anthem, of an orange, of the schoolroom, and so on, would all be object images.  A word or abstract image is one which is a symbol.  It stands for and represents certain sensory experiences, the quality of which does not appear in the image.  Any word, number, mathematical or chemical symbol—­in fact, any abstract symbol will come under this type of image.  If in the first list of illustrations, instead of having images of the real objects, an individual had images of words in each case, the images would be abstract or verbal images.  Abstract images shade into concrete by gradual degrees—­there is no sharp line of division between the two; however, they do form two different kinds of images, two forms which may have the same meaning.

The question as to the respective use and value of these two kinds of images is given different answers.  There is no question but that the verbal image is more economical than the object image.  It saves energy and time.  It brings with it less of irrelevant detail and is more stable than the object image, and therefore results in more accurate thinking.  It is abstract in nature and therefore has more general application.  On the other hand, it has been claimed for the object image that it necessarily precedes the verbal image—­is fundamental to it; that it is essential in creative work dealing with materials and sounds and in the appreciation of certain types of descriptive literature, and that in any part of the thinking process when, because of difficulty of some kind, a percept would help, an object image would be of the same assistance.  It is concerning these supposed advantages of the object image that there has been most dispute.  There is no proof that the line of growth is necessarily from percept, through object image, to verbal image.  In certain fields, notably smell, the object image is almost absent and yet the verbal images in that field carry meaning.  It is also true that people whose power of getting clear-cut, vivid object images is almost nil seem to be in nowise hampered by that fact in their use of the symbols.  Knowing the unreliability of the object image, it would seem very unsafe to use it as the link between percept and symbol.  Much better to connect the symbol directly with the experience and let it gain its meaning from that.  As to its value in constructive work in arts, literature, drama, and invention, the testimony of some experts in each field bears witness that it is not a necessary accompaniment of success.  The musician need not hear, mentally, all the harmonies, changes, intervals;