A half century ago, in The Relations Between State and Federal Law, Professor Henry Hart of Harvard defined the public need for harmonizing the legal dictates issuing from the two levels of sovereignty established in the United States Constitution:
The law which governs daily living in the United States is a single system of law: it speaks in relation to any particular question with only one ultimately authoritative voice, however difficult it may be on occasion to discern in advance which of two or more conflicting voices really carries authority. In the long run and in the large, this must be so. People repeatedly subjected, like Pavlov's dogs, to two or more inconsistent sets of directions, without means of resolving the inconsistencies, could not fail in the end to react as the dogs did. The society, collectively, would suffer a nervous breakdown.. . .