Labor theory of value is a Marxist idea, not an Adam Smith idea. Internet Marxists sometimes point to a passage in The Wealth of Nations to suggest that Smith also supported a labor theory of value, but this is—in the most generous interpretation—a misreading. Smith says that the value of a thing can be measured by how much labor it can be exchanged for: an exchange theory of value, not a labor theory of value (which says the value of a thing is based on how much labor it takes to create).