Full Idea
An 'idealisation' preserves all the properties of the source but it possesses these properties in some ideal or perfect form. ...An 'abstraction', on the other hand, lacks certain features of its source.
Gist of Idea
Idealisation idealises all of a thing's properties, but abstraction leaves some of them out
Source
Rom Harré (Laws of Nature [1993], 1)
Book Reference
Harré,Rom: 'Laws of Nature' [Duckworth 1993], p.35
A Reaction
Yet another example in contemporary philosophy of a clear understanding of the sort of abstraction which Geach and others have poured scorn on.