Final answer:
Merchants had the most impact on Adam Smith's thinking, influencing his seminal work on economic theory, The Wealth of Nations, which emphasized free trade and minimal governmental intervention in the economy.
Step-by-step explanation:
Considering the influential figures in Adam Smith's life and his own work, it appears that merchants had the most profound impact on Smith's thinking. As an economist, Smith was particularly concerned with economic systems and practices, such as those upheld by merchants who were directly involved in commerce and trade. Smith critiqued prevailing mercantilist theories that advocated for protective tariffs and governmental intervention in the economy. His pioneering work, The Wealth of Nations, argued that free trade and competition are essential for economic prosperity, ideas that all resonate with the practices and perspectives of merchants. While scientists and philosophers were also a significant part of the intellectual milieu of the Enlightenment that shaped Smith's work, it was the practical and economic concerns typically associated with merchants that most directly informed his ideas about markets and the economy.
Moreover, Smith's concept of an 'invisible hand' that guides the free market can be seen as emerging from observing the practices and outcomes of merchant trade, rather than abstract philosophical speculation or scientific inquiry. This reinforces the centrality of merchant practices to Smith's economic philosophies.