When you write an argumentative essay, the first thing you need to think about is what point of view you will defend. This will be your thesis, or the main idea of the essay. The rest of the essay will provide arguments that will try to persuade the audience of supporting your point of view.
An outline for this essay would look something like this:
1. Introduction
1.1 What is same sex marriage?
1.2 What is the current status of same sex marriage?
1.3 What is your point of view?
2. Body
2.1 Reasons why same sex marriage should be legal.
2.2 Possible counterarguments.
2.3 Responses to counterarguments.
3. Conclusion (Restate the thesis)
