Entry on "Matter" (Cambridge Dictionary of Philosophy, 3rd. ed) Matter, a notion closely allied with that of a material object. In ordinary language, matter is typically something that material objects are made of, and hence one of their constituent parts. In more scientific contexts, matter is often identified with material objects themselves-or more precisely, with objects possessing spatial extension (or volume) and mass. Matter occupies a special place in traditional Aristotelian philosophy, forming an essential part of the doctrine known as hylomorphism-that is, the view that material objects are compounds of both matter (hyle) and form (morphe). In this context, matter is best thought of as a constituent part of objects and is closely allied with the notion of a substratum. Important philosophical questions arise for matter in the ordinary, scientific, and Aristotelian senses. There are, for example, questions about its nature. Some philosophers draw a sharp distinction between things and stuff. (Things are individuals that can be counted, whereas stuff is non-individual and hence can only be measured.) Is matter best conceived of as a thing or stuff? And in either case, does all matter ultimately belong to a single type. Or are there fundamentally different types of matter? Thales famously asserted that everything can be understood in terms of a single type of matter-namely, water. Others, including some of Aristotle's ancient and medieval followers, distinguished different types of matter for different types of object-one type for terrestrial bodies, another type for celestial bodies, and some even distinguished a type of "spiritual" matter for incorporeal substances, such as angels and the human soul. There is no consensus among contemporary philosophers on these questions. In addition to questions about the nature of matter, there are also questions about its structure or composition. Is matter simple or complex? And if complex, is it discrete-that is, ultimately composed of mereological simples (or atoms)? Or is it rather continuous-that is, such that each of its parts has proper parts, and hence of a type known as "atomless gunk"? Here again, different philosophers have taken different positions. Prior to the rise of modern science, it was common for philosophers to follow Aristotle in conceiving of matter as both complex and continuous. Since the 17th century, however, atomism has come to be the dominant view, though the Aristotelian conception has its share of contemporary supporters, as does the view of matter as an extended simple. See also: Aristotle, atomism, atomless gunk, continua, extended simples, extension, form (accidental, substantial), corporeality, hylomorphism, material object, medieval philosophy, stuff, substratum, substance, thing.