If A originally produces a certain reaction, and A frequently occurs in conjunction with B, B alone will ultimately produce the reaction that A originally produced. For example: if you wish to teach bears to dance, you place them upon a platform so hot that they cannot bear to leave a foot on it for more than a moment, and meanwhile you play "Rule Britannia" on the orchestra. After a time "Rule Britannia" alone will make them dance. Our intellectual life, even in its highest flights, is based upon this principle.
Source: Bertrand Russell : Mind and Matter (1950?)
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