Paul Needham is emeritus professor of theoretical philosophy at the University of Stockholm. He has a first degree in chemistry and a masters degree in philosophy, both from the University of Birmingham, and a doctorate in philosophy from the University of Uppsala. His interests include metaphysics, epistemology and the philosophy of science. He has previously worked on time and tense, causation and subjunctive conditionals. More recent interests are concerned with issues related to chemistry. This includes themes connected to the work of Pierre Duhem, particularly in connection with his role in the establishment of the field of physical chemistry, studies of the origins of the concept of chemical substance in the ancients and its development in more recent times, the discussion of natural kinds and criteria of sameness of substance in modern chemistry, and applications of mereology in the interpretation of macroscopic notions.