Adam Smith’s famous book, "The Wealth of Nations", published 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.