Full Idea
The four couples of elementary qualities attach themselves to the apparently 'simple' bodies (Fire, Air, Earth, Water). Fire is hot and dry, whereas Air is hot and moist (being a sort of aqueous vapour); Water is cold and moist, and Earth is cold and dry.
Gist of Idea
Fire is hot and dry; Air is hot and moist; Water is cold and moist; Earth is cold and dry
Source
Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 330b02)
Book Reference
Aristotle: 'The Basic Works of Aristotle', ed/tr. McKeon,Richard [Modern Library Classics 2001], p.511
A Reaction
This is the traditional framework accepted throughout the middle ages, and which had a huge influence on medicine. It all looks rather implausible now. Aristotle was a genius, but not critical enough about evidence.