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Individuals cannot be atoms - atoms would be all identical because they have the same parts (namely none) - Solution: Proper Parts Principle/strong/SSP/strong supporting-Principle: if x is not part of y, then there is a z, which is part of x, and separated by y - problem: the interval [0,1) is not part of the interval (0.1] (or vice versa) but no part of [0,1) is separated from (0,1] - I.e. that overlapping intervals do not always have a unique product - but extensionality demands that two overlapping individuals have a maximum common part - solution: if x and y overlap, then all parts of the overlapping part are parts of x and parts of y.
Individual/SimonsVsGoodman (Leonard): not every still so abstract concept (plural term) should correspond to an individual - but: to have identity conditions for every individual, is an excessive demand. - That does not work in everyday life.
Parts Oxford New York 1987