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### Single Idea 12826

#### [catalogued under 4. Formal Logic / G. Formal Mereology / 2. Terminology of Mereology]

Full Idea

The 'sum' of two individuals is that individual which something overlaps iff it overlaps at least one of x and y, expressed by 'x + y', read as 'the sum of x and y'. It is central to classical extensional mereologies that any two individuals have a sum.

Clarification

The 'sum' is also known as the 'fusion'

Gist of Idea

Sum: the sum of individuals is what is overlapped if either of them are, written 'x + y'

Source

Peter Simons (Parts [1987], 1.1.06)

Book Reference

Simons,Peter: 'Parts: a Study in Ontology' [OUP 1987], p.14

A Reaction

This rather technical definition (defining an individual by the possibility of it being overlapped) does not always coincide with the smallest individual containing them both.

Related Idea

Idea 14984
Which should be primitive in mereology - part, or overlap? **[Sider]**