Final answer:
John Adams is using an appeal to historical precedent and common agreement in his letter, arguing for representation in colonial legislatures instead of British Parliament, which aligns with the broader colonial rejection of the British concept of virtual representation.
Step-by-step explanation:
In John Adams' letter to a fellow colonist who supported the king, he is using an appeal to historical precedent and common agreement to argue for representation within their own colonial legislatures rather than in the distant British Parliament. He acknowledges the impracticality of colonial representation in the British Parliament, something that had been recognized for over a century as the colonies were being settled. Adams underlines that as a consequence, the colonies must have representation in their supreme legislatures, reflecting principles already established by kings, ministers, ancestors, and the nation. This ties into the broader American argument against virtual representation advocated by the British, which countered that Parliament represented the interests of all British subjects, even those in the colonies, without the need for actual representatives from the colonies present in the Parliament.