 According to Whitehead, the failure to lay due emphasis on the perceptual mode of causal efficacy implies the danger of reducing the scientific method to Hume’s sensationalist empiricism, and ultimately lies at the basis of the Humean failure to acknowledge the relatedness of nature, especially the causal relatedness of nature. Indeed, “the notion of causation arose because mankind lives amid experiences in the mode of causal efficacy” (1929c [1985: 175]). According to Whitehead, “symbolic reference is the interpretative element in human experience” (1929c [1985: 173]), and “the failure to lay due emphasis on symbolic reference … has reduced the notion of ‘meaning’ to a mystery” (1929c [1985: 168]), and ultimately lies at the basis of Newton’s failure to give meaning to his formulae of motion and gravitation.