Cunningham and Kusukawa present both a translation of a useful primary source and an argument in Cunningham's ongoing debate over the nature of natural philosophy. Gregor Reisch's Philosophical Pearl is an epitome, a text intended to produce a summation of the entirety of philosophy as an educational tool for university students. It follows the course of the university philosophy curriculum and is known to have been used by university students, but was not produced as a course book. It was a distillation of the Aristotelian philosophy, and an aid to its understanding. The version of the text translated by Cunningham and Kusukawa is the original edition of 1503 and includes, placed within the text of the translation, the original figures drawn by Alban Graf to accompany the text. Philosophical Pearl was a popular and widely used work, reprinted twelve times before the end of the sixteenth century. Cunningham and Kusukawa argue that an exploration of this work, and particularly of the four books that Reisch identifies as natural philosophy, may help modern scholars achieve a better understanding of the nature of natural philosophy in the sixteenth century.

The translator's introduction carries the tone of Cunningham's arguments from his previous work. It suggests that historians of science tend to use definitions of natural philosophy that are formed more by modern opinions about what should be considered ‘science’ than by the contemporary views on what should be included in a discussion of natural philosophy. In framing this work Cunningham and Kusukawa wish to show the reader the complexity of the subjects considered under Reisch's concept of natural philosophy. They particularly point out that the interest in investigating nature is fundamentally a religious one. The natural world is investigated as a means of understanding the project of the Creator and to talk about creatures or creation is to talk about the Creator. Possibly in deference to the reception Cunningham's claims have received previously, he and Kusukawa present the translation of books eight to eleven of Philosophical Pearl, the four books identified by Reisch as concerning natural philosophy, as evidence supporting these claims. They invite the reader to allow the text to define the scope of natural philosophy.

In Philosophical Pearl, Reisch explicitly gives consideration to the divisions of philosophy and categorizations of knowledge. He divides the manuscript up into seven books on the liberal arts, four books on natural philosophy, and a final book on moral philosophy. As the translator's introduction leads the reader to expect, the questions covered by these four books of natural philosophy create a very different picture of the concerns of natural philosophy than some modern scholars might expect. The section on natural philosophy begins with Book 8, titled ‘On the principles of natural things’. This book opens with an image of the Creation and deals with the forms of nature and the act of Creation. It is particularly concerned with bringing together the opinions of philosophers and Scripture. In Chapter 2 we are presented with a summary of the opinions of philosophers on Creation, in Chapter 3 we see the opinion of Moses and Chapter 4 attempts to show the concordance of opinions. Throughout his work Reisch attempts to show agreement between philosophers and Scripture, or to show how their statements are subject to different modes of interpretation while both remaining true. Book 9 also opens with the figure of the Creation, but deals with the created world, the origins of natural things, rather than with the first principles of Creation. It opens with a statement that understanding the origins of natural things is impossible by human power alone and requires the aid of the Creator. Book 9 builds from discussion of the origins of the elements to discussion of the particulars of the world. It concerns the natures and generation of things, weather, animals and humans – the questions we would expect from a text on natural philosophy. Book 10 deals with questions of the nature and aspects of the sensitive soul. It explores the means by which the sensitive soul engages with the world and the process of cognition and understanding. The final book on natural philosophy, Book 11, deals with a set of questions that many modern scholars might not include in their classification. It concerns the nature, origin and immortality of the intellective soul. This book is particularly interesting to Cunningham and Kusukawa because it not only discusses the nature of the intellective soul as a natural object but also traces it from generation to immortality and resurrection. Book 11 even ends on a set of questions concerning the intellective soul's ability to experience torment in Hell and whether it can burn for eternity without being consumed. Reisch's account of natural philosophy tells the story of the natural world from Creation to destruction, and the life of the soul afterwards.

The translated books of Philosophical Pearl do seem to support Cunningham and Kusukawa's idea of natural philosophy fundamentally enmeshed with religion. Certainly in Reisch's view to talk about the natural world was to talk about Creation and the Creator. They argue that at its most basic Reisch's concept of natural philosophy might be limited to Aristotle's Physics, but the Philosophical Pearl shows the breadth natural philosophy could take on. Its extensions encompass all the works of nature and, as we see in Book 11, the course of the Christian soul. Gregor Reisch includes matter we would consider appropriate to theological speculation in the books he identifies as concerning natural philosophy. If we are to understand natural philosophy accurately we cannot disassociate it from theology every time we see them together. Considering the repeated printing of this book and the evidence of its widespread use, any scholar wishing to understand the nature of natural philosophy at the end of the fifteenth century must engage with – and, the translators argue, begin with – Philosophical Pearl.