A vast number of traditions have existed over time that one could conceivably categorise as religions. But in order to decide one way or the other, an observer first has to formulate a definition according to which some traditions can be included and others excluded. As Jonathan Zitell Smith wrote in the introduction to Imagining Religion: ‘while there is a staggering amount of data, of phenomena, of human experiences and expressions that might be characterised in one culture or another, by one criterion or another, as religious – there is no data for religion’.