cbf94194_Euclid_5_Intro_html__Definitions
[0] 4. [Brief comments] Some have read this as stating a basic principle about continuity and what it is for two magnitudes to be of the same kind. Knorr pointed out that this actually sets up necessary conditions for the next definition. Is this a definition? [Definitions] 
Magnitudes which are able by being multiplied to exceed one another are said to have a ratio to one another.
Euclid.5.Intro.html
Definitions