Full Idea
Secondary qualities are caused by a mixture of primary qualities.
Gist of Idea
The primary qualities are mixed to cause secondary qualities
Source
Walter Burley (De formis [1330], pars post p.65), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 21.2
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.462
A Reaction
Like paint. He probably has in mind hot, cold, wet and dry as the primary qualities.