The Buddha once said this to the Bhikkhus:
"Bhikkhus, as to the source through which perceptions and notions tinged by mental proliferation beset a man: if nothing is found there to delight in, welcome and hold to,
When beauty is abstracted
Then ugliness has been implied;
When good is abstracted
Then evil has been implied.
So alive and dead are abstracted from nature,
Difficult and easy abstracted from progress,
Long and short abstracted from contrast,
High and low abstracted from depth,
Song and speech abstracted from melody,
After and before abstracted from sequence.