Edmund Husserl is perhaps the only philosopher of the past one hundred years or so who claims that we can intuit essences and, moreover, that it is possible to formulate a method for intuiting essences. Husserl calls this method ‘free variation in imagination’ or ‘ideation’. It is explicated in some of his writings as the ‘eidetic reduction’. His descriptions of ideation can be viewed as attempts to describe a method appropriate to the a priori sciences, a method that does not reduce to the methods of the empirical sciences. The best and clearest examples of this method, it seems to me, are to be found in mathematics. Pure mathematics, according to Husserl, is concerned with exact essences. Husserl's own examples of the method, however, are often concerned with the inexact (or ‘morphological’) essences of everyday sensory objects (e.g., color, sound) or of the phenomena that form the subject matter of phenomenology itself (consciousness, intentionality, and the like). It is unfortunate that Husserl does not give more examples involving mathematics. He seems to focus on the nonmathematical cases because he is very concerned to show that phenomenology itself can be a kind of science, a descriptive science of the essential structures of cognition. Perhaps he thinks it is not necessary to dwell on mathematics, which, unlike phenomenology, is already a firmly established science.

Husserl's views on intuiting essences have been subjected over the years to extensive discussion, criticism, and even ridicule.