## Abstract

Say that some things *compose* something, if the latter is a whole, fusion, or mereological sum of the former. Then the thesis that composition is identity holds that the *composition* relation is a kind of identity relation, a plural cousin of singular identity. On this thesis, any things that compose a whole (taken together) are identical with the whole. This article argues that the thesis is incoherent. To do so, the article formulates the thesis in a *plural language*, a symbolic language that includes counterparts of plural constructions of natural languages, and shows that it implies that nothing has a proper part. Then the article argues that the thesis, as its proponents take it, is incoherent because they take it to imply or presuppose that some things have proper parts.

## Keywords

Composition Identity Plural logic Mereology Composition as identity Many-one identity Eleatic monism Mereological sum Fusion Part/whole Part-whole triviality## Notes

### Acknowledgements

The work for this article was supported in part by a SSHRC Insight Grant [Grant No. 435-2014-0592], which is hereby gratefully acknowledged. I presented its previous versions in the Mereology and Identity Workshop and at Nihon University. I would like to thank G. Lando, M. Carrara, and T. Iida for the invitations and the audiences for their comments and discussions. I would also like to thank two anonymous referees for *Synthese* for helpful comments on the penultimate version, P. Hovda for discussions on topics of this article, and Y. El Gebali and E. Darnell for editorial assistance. The penultimate version of this article was written while I was visiting Hokkaido University as a visiting scholar in 2018. I am grateful to T. Yamada and K. Sano for their invitation and hospitality during the visit. Needless to say, I am solely responsible for any errors and infelicities in this article.

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