This chapter explains what Husserl meant by a "mathematics of the mind", (IX, 50) as creating an eidetic method that makes theoretical ideals to support empiricism. Mathematics has the specific sense of observing diverse phenomena and finding the commonalities between them. What people ordinarily experience is the natural attitude of the lifeworld of unclarified objects and processes of the production of meaning. The way of analysing and interpreting what appears aids understanding and action because of its ability to refer to specific moments and constant of universal relations within the whole of meaning. This chapter introduces eidetics by setting the scene through making reference to the success of various types of mathematics in the service of physics by brief overviews of how mathematics has been successful in mapping natural being and its causes. The point is that eidetics is a type of conceptualisation where, in a broad sense, the natural world is mapped and interpreted. The major teaching point of the chapter is understanding the progression from the natural attitude to transcendental philosophy of conditions of possibility to win eidetic conclusions and use them in the natural attitude once more. The analogy that Husserl was following in proposing "philosophy as rigorous science" is an eidetics of how consciousness works in intersubjectivity in presenting being. The formula "A.B ~ C" is used as a shorthand for the commonality between eidetics (in the pure psychological or transcendental attitudes) that interpret noetic-noematic moments. The universal essences seen make sense of the noeses and noemata that comprise objects and their regions. The formality of the language hides a great deal because what is being referred to by the shorthand expression "seeing essence" requires further explanation. Seeing essence is a more abstract higher order reflection on wholes of sense expressed across many areas of life. This is because seeing essences refers to a variety of forms of understanding, not just one. Although, to spot a pattern at the highest formal level of seeing essences is always to be reliant on noting different types of intentionality and different types of noemata. Later sections below explain the novel qualitative methods for making theoretical ideals which are what phenomenology offers to support future empirical projects. This chapter considers the merely possible as a way of keeping questions open and preventing foreclosure and dogmatism.