Full Idea
Based on perceiving the presence of some attribute, we conclude there must also be present an existing thing or substance to which it can be attributed.
Gist of Idea
If we perceive an attribute, we infer the existence of some substance
Source
René Descartes (Principles of Philosophy [1646], I.52), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 08.1
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.136
A Reaction
A rainbow might be a tricky case. This illustrates the persistent belief in substances, even among philosophers who embraced the new corpuscular and mechanistic view of matter.