There has been a long academic debate on what makes services different from goods. The historical perspective in the late-eighteen and early-nineteenth centuries focused on creation and possession of wealth. Classical economists contended that goods were objects of value over which ownership rights could be established and exchanged. Ownership implied tangible possession of an object that had been acquired through purchase, barter or gift from the producer or previous owner and was legally identifiable as the property of the current owner. Adam Smith’s book The Wealth of Nations, published in Great Britain in 1776, distinguished between the outputs of what he termed "productive" and "unproductive" labor. The former, he stated, produced goods that could be stored after production and subsequently exchanged for money or other items of value. The latter, however useful or necessary, created services that perished at the time of production and therefore did not contribute to wealth. Building on this theme, French economist Jean-Baptiste Say argued that production and consumption were inseparable in services, coining the term "immaterial products" to describe them.