An argumentative essay is a chance to hone your reasoning and research skills. While debates with friends and family over ethics can be emotionally charged, an academic essay should be a logical, well-reasoned presentation of an issue. It should emphasize why your approach makes more sense than another point of view. Because ethics is a broad and complex topic, it's wise to craft a very specific thesis and ensure that your paper addresses a single specific issue that can be exhaustively covered in a few pages.
Before you begin writing your paper, you'll need to research the topic you've chosen. You'll likely have to draw on several authoritative sources to support your arguments, and you should be familiar with what other people have said about the issue. Sketch an outline of your paper, focusing on supporting your main idea and how you'll develop each part of your argument. List all sources and references you find for each argument or sub-topic. Your outline can help you avoid adding unnecessary information and makes it easier to craft a paper with a strong, logical structure.
Every argumentative essay needs a clear thesis that succinctly summarizes the central argument and identifies its main supporting points. Your thesis should be in the first paragraph of your essay. This paragraph introduces the topic by providing relevant background information and explaining why the topic is important. It should end with your thesis statement. Unless your paper is very long, a narrow, focused thesis is ideal because you'll be able to fully address the idea in the length of your paper. For example, rather than write, "The death penalty is wrong," you might argue that, "The potential for executing an innocent person makes the death penalty a risky and unjustifiable punishment that violates the U.S. Constitution."
The body paragraphs of your essay should help develop and explain your argument. You can devote one paragraph to each sub-argument or researched source. You might, for example, devote one paragraph to statistics on wrongful death penalty convictions, another paragraph to an argument about the U.S. Constitution and the death penalty, and spend another paragraph explaining a philosopher's anti-death penalty argument. These arguments should be clearly developed without extraneous information, and each should neatly relate to your thesis. For example, you don't need to talk about wrongful convictions in general or problems of incarceration on an essay about the death penalty.
A good argumentative essay anticipates potential objections to your argument and treats these arguments charitably. Don't mischaracterize a philosopher's argument to make your point look stronger. Instead, draw attention to weak points in the argument or explain why this argument might not fully discredit your idea. In a death penalty essay, you might write, "Some philosophers have expressed concern that eliminating the death penalty will increase crime." Point to a few people who make this argument and explain their points. Then emphasize why this argument might not be completely relevant to your essay, for example, by discussing crime rates in places that don't have the death penalty.