An ethical appeal, according to Aristotle's rhetorical situations, derives from "ethos," the idea that you are more easily persuaded to agree with a point of view if the speaker has credibility. If you feel an author is trustworthy and speaks with your best interests in mind, his appeals are ethically sound to you. Authors and speakers work to present a favorable and ethical image to their audiences because they must appear worthy of your attention for you to accept what they say.
Ethical History Equals Credibility
A speaker attempting to win an ethical appeal will usually refer to his personal history to lend credibility. A doctor will cite his medical credentials to appeal to you as a patient to try his course of treatment. A scientist will let his experimental expertise convince you that his conclusions are correct. A politician will point to his exemplary record of public service to get your vote. Even your elders will use their age and relationship to you to convince you that their opinions are correct ones.
Be Careful of Ethos Intruding
When someone you know well tries to argue based on your relationship, this actually slides the argument into pathos, the Aristotelian name for emotionally based reasoning, which is much less trustworthy even if it assumes the guise of ethics. "I love you, therefore I'm right," may be a semivalid ethical appeal for a grandfather, while an abusive husband using this argument is far less credible. A master of making pathos arguments appear ethical, Adolf Hitler is a prime example of the horrific danger of mixing these two appeals into believable arguments.
Ethical Appeals with Historic Background
The best ethical appeals are indeed rooted in emotion -- no speaker argues what he does not feel strongly about -- but communicate a straightforward, believable motivation. An example is Patrick Henry's "Give Me Liberty or Give Me Death" speech. Henry, well known to his audience as lawyer and orator, had previously protested the Stamp Act and supported the colonists' right to bear arms. His patriotism and fervor were already well known, making his appeal credible.
Ethos Equals Character
If you want to create your own ethical appeal, remember that "ethos" is Greek for "character." If possible, choose an audience that knows your character well. No matter what group you speak to, however, choose language and vocabulary suitable for their level, and be unbiased in the presentation of your point of view, remembering to acknowledge the opposing side. Remind your listeners of your credentials and treat them with respect and courtesy to make your appeal credible and ethical.