A. de Vries 
Finite Automata [PDF ebook] 
Behavior and Synthesis

This dictionary supplies associations which have been evoked by certain words, signs, etc. in Western civilization in the past, and which may float to the surface again tomorrow; for however ‘daringly new’ a modern use of imagery may look, it generally appears to have roots in what has been said and done in the past. No fine distinctions have been made between symbols (in the limited sense), allegories, metaphors, signs, types, images, etc. (not to mention ‘ascending’ and ‘descending’ symbols), since such subtle distinctions, however sensible from a scientific point of view, are useless to a person struggling with the deeper comprehension (and thus appreciation) of a particular ‘symbol’.