Full Idea
Things are similar to the extent that they are interchangeable parts of the cosmic machine.
Gist of Idea
Similarity is just interchangeability in the cosmic machine
Source
Willard Quine (Natural Kinds [1969], p.134)
Book Reference
Quine,Willard: 'Ontological Relativity and Other Essays' [Columbia 1969], p.134
A Reaction
This is a major idea for Quine, because it is a means to gradually eliminate the fuzzy ideas of 'resemblance' or 'similarity' or 'natural kind' from science. I love it! Two tigers are same insofar as they are substitutable.
Related Idea
Idea 16948 Once we know the mechanism of a disposition, we can eliminate 'similarity' [Quine]