In 1767 Forbonnais published the Principes et observations oeconomiques with the declared intent of challenging the scientific validity of the Tableau économique, despite the fact that in 1759 ‘he had been one of its keenest readers, just as Quesnay had been of his Recherches et considérations sur les finances de France depuis l'année 1595 jusqu’à l'année 1721’. Indeed, the relationship between Quesnay, the court physician who had given himself to the study of the economy, and Forbonnais, the inspecteur général des monnaies de France (from 1756) and economic advisor to the contrôleur général Étienne de Silhouette, was strong, as the letters that the former sent to the latter during 1758 attest. In one dated 14 September, Quesnay had expressed his appreciation for Forbonnais's ideas ‘on circulation’, saying these were ‘the only way to conceive of it in reality and truth’. Quesnay praised him for having avoided the trap of tracing the origins of the wealth of a nation by taking into account only the circulation of money. However, in the same letter he invited Forbonnais to follow a new path to analyse that circulation: in carrying out his research and ‘assessment’ Forbonnais needed to bear in mind

Quesnay also stated that it was necessary to distinguish between

In essence, despite continuing to maintain that foreign trade could lead to a net profit, in this letter to Forbonnais, Quesnay had anticipated the key arguments of his Tableau in which, significantly, the possibility that foreign trade could produce a net profit disappeared.