We have given examples and illustrations in the paragraph describing Conversion by contraposition.
It is for dealing with these intractable moods that contraposition is required.
In this it differs from Obversion, Conversion, and contraposition, each of which stands for one process.
A further process, known as contraposition or Conversion by Negation, consists of conversion following on obversion.
They are all remarkable for harmonies attained by certain combinations of shade in gradations with colours in contraposition.