It may safely be assumed that this was not done capriciously, as the modern parvenue makes for himself a heraldric device. The simple and devout intellect of the primitive man imagined a real connection between the god and the symbol. Were this questioned, yet the wonderful unanimity with which the same natural objects, the serpent, the bird, the tree, for example, were everywhere chosen, proves that their selection was not the work of chance. The constant preference of these objects points conclusively to some strong and frequent connection of their images with mythical concepts. The question of the origin of symbols therefore resolves itself into one of the association of ideas, and we start from sure ground in applying to their interpretation the established canons of association. These, as I have elsewhere said, are those of contiguity and similarity, the former producing association by the closeness of succession of impressions or thoughts, the latter through impressions or thoughts recalling like ones in previous experience. When the same occurrence affects different senses simultaneously, or nearly so, the association is one of _contiguity_, as thunder and lightning, for a sound cannot be _like_ a sight; when the same sense is affected in such a manner as to recall a previous impression, the association is one of _similarity_, as when the red autumn leaves recall the hue of sunset. Nearness in time or nearness in kind is the condition of association. The intensity or permanence of the association depends somewhat on temperament, but chiefly on repetition or continuance. Not having an ear for music, I may find it difficult to recall a song from hearing its tune; but by dint of frequent repetition I learn to associate them. Light and heat, smoke and fire, poverty and hunger so frequently occur together, that the one is apt to recall the other. So do a large number of antithetical associations, as light and darkness, heat and cold, by _inverse similarity_, opposite impressions reviving each other, in accordance with the positive and privative elements of a notion.