Full Idea
All our complex ideas are ultimately resolvable into simple ideas, of which they are compounded and originally made up.
Gist of Idea
Complex ideas are all resolvable into simple ideas
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.22.09)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.292
A Reaction
This can certainly be challenged. I guess we form the concept of a 'bird' before we form the concept of a 'feather'. How ideas are arrived at is quite different from ways in which they can be analysed and broken down.