Jefferson's observation cuts against the Enlightenment materialism of his own era—a time when natural philosophers were busily cataloging the measurable world and reducing value to utility and exchange. What he's really defending here is the irreducible worth of contemplation itself, that moment when a thought arrives and warms you from within, resisting any accounting. A person who has experienced genuine intellectual delight—say, finally understanding why a friend forgave them, or seeing how a failure actually taught them something essential—knows that no sum of money could replicate that private illumination. Jefferson knew that the rich man without such moments lives in genuine poverty, while even modest circumstances become livable when the mind still glows.