This paper presents a comprehensive study of Robert Boyle’s writings on seminal principles or seeds. It examines the role of seeds in Boyle’s account of creation, the generation of plants and animals, spontaneous generation, the generation of minerals and disease. By an examination of all of Boyle’s major extant discussions of seeds it is argued that there were discernible changes in Boyle’s views over time. As the years progressed Boyle became more sceptical about the role of seminal principles in the (...) generation of minerals and he came to reject the spontaneous generation of insects and animals from putrefying matter. It is also argued that Boyle’s notion of a generative or ‘plastick’ principle creates a tension within his mechanical philosophy. He appeals to a plastick power in order to explain those phenomena of generation that are beyond the explanatory resources of the corpuscular hypothesis. However, when pressed to explain the nature of this power he either hints, somewhat paradoxically, that it too can be explained mechanically or admits his nescience. (shrink)