Final answer:
William Pitt used the Declaratory Act to express his opinion on the Stamp Act in his speech. This law echoed his sentiments about the relationship between Britain and the colonies and affirmed Parliament's authority over American laws, following resistance to the Stamp Act.
Step-by-step explanation:
The law that William Pitt is known to have referenced in his speech concerning the Stamp Act is likely the Declaratory Act of 1766. The Declaratory Act was a piece of legislation which affirmed that Parliament had the same authority in America as in Britain and could pass laws binding the colonies in all cases whatsoever. It was a response to the colonial resistance to the Stamp Act. Pitt's sentiments that Parliament should not tax the colonies without their consent were reflected in the Declaratory Act, which sought to clarify the relationship between Britain and the American colonies, following the uproar caused by the Stamp Act.
The Stamp Act itself was introduced by Prime Minister Grenville and passed by the British Parliament in 1765, imposing a direct tax on the colonists and requiring them to pay for a revenue stamp for all types of printed paper used, including newspapers and legal documents. This act led to violent protests in the colonies and the slogan 'no taxation without representation,' as the colonists had no representatives in the British Parliament to voice their opinions on such taxes. The Stamp Act was seen as an attempt by Britain to assert its power over the colonies, leading to a fundamental challenge to British authority by the colonial leaders.