Final answer:
The colonists did not believe the British had the right to tax them unless they had direct representation in Parliament, a belief influenced by British legal traditions and their own political ideologies that emphasized direct representation and consent for taxation.
Step-by-step explanation:
The colonists did not believe the British had the right to tax them unless they had representation in Parliament. This principle stemmed from the belief that taxation was legitimate only if the taxed individuals or their elected representatives had consented to it.
Possible representation through Parliament, which was the case for British subjects back in England, was not seen as adequate by the colonists because they weren't allowed to vote for any members of the Parliament. Thus, the rallying cry of "no taxation without representation" encapsulated their demand for direct political representation if they were to be subject to parliamentary taxation.
The colonists' insistence on this principle was rooted in their understanding of British constitutional law, specifically the rights outlined in the Magna Carta and the English Bill of Rights. Their stance was reinforced by the colonial political systems, which revolved around the concept of direct representation. When Parliament introduced taxes like those from the Stamp Act to pay for the defense of the colonies and the upkeep of British soldiers, the colonists rejected the authority of Parliament to impose such taxes without colonial representation, leading to acts of protest and calls for liberty under the British Constitution.