Full Idea
A set of determinates under the one determinable are incompatible by definition. If an object is not one mile in length, then its actual length will be incompatible with being one mile in length.
Gist of Idea
The determinates of a determinable must be incompatible with each other
Source
David M. Armstrong (Truth and Truthmakers [2004], 05.2.1)
Book Reference
Armstrong,D.M.: 'Truth and Truthmakers' [CUP 2004], p.62
A Reaction
This is a much better general version of the standard example 'if it is red it can't be green'. Armstrong uses it to give a more precise account of incompatibility. Useful.
Related Idea
Idea 18378 Length is a 'determinable' property, and one mile is one its 'determinates' [Armstrong]