Journal Article

Substance and Time

Paul Needham

in The British Journal for the Philosophy of Science

Published on behalf of British Society for the Philosophy of Science

Volume 61, issue 3, pages 485-512
Published in print September 2010 | ISSN: 0007-0882
Published online February 2010 | e-ISSN: 1464-3537 | DOI:
Substance and Time

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‘Water is H2O’ is naturally construed as an equivalence. What are the things to which the two predicates ‘is water’ and ‘is H2O’ apply? The equivalence presupposes that substance properties are distinguished from phase properties. A substance like water (H2O) exhibits various phases (solid, liquid, gas) under appropriate conditions, and a given (say liquid) phase may comprise several substances. What general features distinguish substance from phase properties? I tackle these questions on the basis of an interpretation of a theorem of thermodynamics known as Gibbs' phase rule which systematically relates these two kinds of feature of matter. The interpretation develops the idea that the things substance and phase predicates apply to are quantities of matter which sustain mereological relations and operations and exploits these mereological features in distinguishing the two kinds of property. Gibbs' phase rule is a macroscopic principle applicable for macroscopic intervals of time. Bringing intervals of time into the picture calls for a more detailed consideration of the relation between macroscopic equilibria and the corresponding dynamic equilibria at the microlevel and throws into question the simple idea that quantities can always be regarded as collections of molecules. The account provides some insight into how the continuous, macroscopic conception of matter (‘gunk’) is reconciled with the discrete microscopic conception and illuminates the interpretation of substances present in mixtures.


Time Dependence


Criteria of Purity and the Notion of Substance

Derivation and Further Illustrations of the Phase Rule

Microscopic Species in Water

Dynamic Equilibria and the Phase Rule

The Time of Predication

Independent Substances

The General Conception of a Mixture


Journal Article.  12162 words.  Illustrated.

Subjects: Philosophy of Science ; Science and Mathematics

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