Hansel's Reconstruction, and Why the Argument Is About Architecture

Thirty years later the psychologist C. E. M. Hansel visited Duke, examined the buildings and produced the criticism that has dominated discussion of the series ever since. His argument was not that Pearce had cheated but that the design did not make cheating impossible, and in an experiment offering a conclusion this large that distinction matters. Pearce was unobserved in the library for the duration of each session. Hansel argued that he could have walked to the building where Pratt was working and observed the cards from outside the room, and he specified how, drawing on the layout of doors and the position of the desk.

Rhine and Pratt replied in detail, disputing the sightlines and the timing and pointing out that Pearce would have had to be absent from the library without anyone noticing. Neither side conceded and the buildings have since been altered. What makes this exchange worth recording is the shape of it. Both parties agree the arithmetic is correct and both agree the result is decisive if the separation held, so the entire weight of one of the most cited experiments in the field rests on a question about a doorway. The general lesson, that a control which depends on nobody having checked an unobserved person is not a control, was absorbed into later protocol design.