Thomas Holden presents a fascinating study of theories of the structure and internal architecture of matter in the seventeenth and eighteenth centuries. Are the parts of material bodies actual or potential entities? Is matter infinitely divisible? Do all material bodies resolve to actual first parts? All the great philosophers and philosopher-scientists of the period address these issues, including Galileo, Descartes, Newton, Hume, and Kant. Holden offers a brilliant synthesis of these discussions and his own overarching interpretation of the debate.