Locke. book 2, chapter 31

I don't quite understand Locke's definition of adequate. He breaks ideas into two groups. One seems to be "simple" depending on archtype and the other "a partial or incomplete representation of those archetypes". What is the difference between ideas being adequate or ideas of substances. I believe all educated ideas have substance to them simple or not. I feel Descartes was a little more clear when it came to concepts and ideas that were new to a reader.