Note: Much of the material in this post was taken from comments which originally appeared in this thread at http://www.humantransit.org, Jarrett Walker's excellent transit blog. It has been significantly edited for the current article.
One famous treatise in the field of psychology is Abraham Maslow's Hierarchy of Needs, which arranges human needs in a hierarchy from basic survival needs (food, water) at the bottom, to more abstract sources of happiness (self-actualization and such) at the top. The paper was controversial when written, and is still controversial, but its influence on the field cannot be disputed.
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