For Margaret Cavendish, every single part of matter has self-knowledge, and almost every part has perceptive knowledge. This paper asks what is at stake for Cavendish in ascribing self-knowing and perceptive properties to matter. Whereas many commentators take perception and self-knowledge to be guides to Cavendish’s epistemology, this paper takes them to be guides to her metaphysics in that it shows that these categories account for individual specificity and for relationality. A part of matter is a unique individual insofar as it is self-knowing – and it is a part in relation to other parts, and to the whole of matter insofar as it is a perceptive part. This is so because self-knowledge is purely self-referential and complete, while perceptive knowledge is purely relational.