Elias St. Elmo Lewis is generally, though perhaps erroneously, credited for conceptualizing the customer journey as a series of four stages: awareness, interest, desire and action, now commonly known by the acronym AIDA. In his 1924 book Bond Salesmanship, author William W. Townsend took things a step further when he combined Lewis' model with the now-popular "purchase funnel." This is where customers begin their journey as part of a large pool of potential buyers who shrink in number as marketing practices push them toward a final sale.