In our September issue, Michael Dertouzos wrote a column, "Not by Reason Alone," that took Bill Joy of Sun Microsystems to task for a piece Joy had written in Wired. In his Wired article, Joy argued that humanity should renounce certain lines of research, including nanotechnology, because of the dangers they pose. Dertouzos argued that Joy's view was flawed because his predictions were based on reason which, taken alone, is an inadequate guide to the future. Dertouzos' column drew an impassioned response from Ray Kurzweil, author of The Age of Spiritual Machines. We print Kurzweil's letter and Dertouzos' rejoinder.

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