According to Aristotle, the role of rhetoric in speeches is to persuade the listener of the orator's point of view. This is not to say that the orator will be successful in doing so, but that the point of the speech is to achieve that aim. Different types of rhetoric in speeches have different aims; some speeches are aimed at persuading people to vote for a particular law or person, others are used to persuade people to change their opinions, and, in extreme cases, speeches can be used to stir up revolution and violence. When all is said and done, the role of the speech is to get people listening to do what the speaker wants done.
Aristotle defined rhetoric as an act of persuasion. In terms of speeches, rhetoric is one person's attempt to persuade many people in his or her audience. Aristotle believed that the rhetorician or orator needs to master all the methods of the craft in order to succeed in the role of rhetoric in speeches. He also believed that rhetoric needed to be neutral and not subjective, meaning that the act of persuasion is based on objective opinion. Not all rhetoricians agree, however.
The role of rhetoric in speeches is much the same as the role of other forms of discourse. It has played an important role in the development of thoughts, movements and politics across the world. What divides it from dialectics is that rhetoric is not followed by a counter position, and it also does not entail any discussion. Rhetoric is a one-way system of conveying information and opinion.
Rhetoric in speeches has had an important role in democracies over the world. Speeches provide politicians with a platform to persuade people to vote for them or their causes. While using rhetoric in this fashion is important, it isn't always vital for a politician's success. Some politicians, like US President Barack Obama and UK Prime Minister Tony Blair, mixed rhetoric with charisma to help win power; George W. Bush's lack of oratory skills did not hinder his rise to the top political office in America. The ancient Roman philosopher Cicero, who was known for his rhetorical skills, was not able to use those skills to gain power.
Few electioneering speeches have helped form a national conscience, but a larger number of political speeches regarding key issues have. One pivotal speech in the shaping of modern America is Martin Luther King Junior's "I Have a Dream" speech. Such speeches transcend their original role of changing opinions of the immediate listeners and help shape the opinions of subsequent generations as well.
Rhetoric does not always play a positive role in society and history. The magnetic power of Adolf Hitler's rhetoric is blamed for continuing not only the Nazi atrocities across Europe, but also in preserving the regime long after the war had been lost. Rhetoric in speeches has the power to provoke, to denounce, and to raise people to actions they might not take without it. With such a powerful role over shaping opinions come great responsibilities on the part of the rhetorician.