"An idea, a mental image, is a complicated thing, and needs perhaps a whole sentence to describe it accurately, so a salient incident in it is seized, and the word naming this incident imperfectly represents the whole; we say “triangle,” and the word calls up in the hearer's mind a picture, which would need a long description if fullv conveyed in words; we do our best thinking in symbols, and then laboriously and imperfectly summarise our symbols into words."