In psychology, the methodological conviction that only the body’s measurable physical responses to stimuli can be used to determine the true nature of psychological states. The most well-known example of this approach is Pavlov’s experiments with dogs, showing that the sound of the dinner bell was sufficient to stimulate a saliva response. The most prominent exponent of this form of psychology was B. H. Skinner, who tried to show that humans act according to experience, rather than intention. The problem with this account of human behaviour, apart from its obviously mechanistic modelling, is that it cannot account for human inventions that cannot have been caused by mere accident. For example, the malleability of copper wasn’t discovered by accidentally dropping copper ore into a cooking fire because it doesn’t melt at that temperature, but needs superheating, which requires the application of engineering principles. The same can be said for virtually all cognitive achievements, they are not explainable as reactions to stimuli.