There is no doubt that the picture of thoughts is made by the impressions of the mind. If the mind has had no impressions thoughts will not be clear. For instance, a blind person who has never in his life seen an elephant, will not be able to form an idea of an elephant, because his mind has no form ready to compose it at the command of his will. For the mind must know it first in order to compose it. Therefore the mind is a storehouse of all forms which a person has ever seen.