I define a symbol in terms of its structure and function. First, a symbol can only exist in the context of a living organism or its artifacts. Life originated with symbolic memory, and symbols originated with life. I find it gratuitous to use the concept of symbol, even metaphorically, in physical systems where no function exists. Symbols do not exist in isolation but are part of a semiotic or linguistic system. H. H. Pattee (1969: 292)