C. D. Broad, Herbert Feigl, and Thomas Nagel, over a fifty-year span, presented insight to the subject, which led to Jackson's proposed thought experiment. Broad makes the following remarks, describing a thought experiment where an archangel has unlimited mathematical competences: He would know exactly what the microscopic structure of ammonia must be; but he would be totally unable to predict that a substance with this structure must smell as ammonia does when it gets into the human nose.