Perhaps it is helpful to think of an essay in terms of a conversation or debate with a classmate. If I were to discuss the cause of World War II and its current effect on those who lived through the tumultuous time, there would be a beginning, middle, and end to the conversation. In fact, if I were to end the argument in the middle of my second point, questions would arise concerning the current effects on those who lived through the conflict. Therefore, the argumentative essay must be complete, and logically so, leaving no doubt as to its intent or argument.
The function of an argumentative essay is to show that your assertion (opinion, theory, hypothesis) about some phenomenon or phenomena is correct or more truthful than others'. The art of argumentation is not an easy skill to acquire. Many people might think that if one simply has an opinion, one can argue it successfully, and these folks are always surprised when others don't agree with them because their logic seems so correct. Argumentative writing is the act of forming reasons, making inductions, drawing conclusions, and applying them to the case in discussion; the operation of inferring propositions, not known or admitted as true, from facts or principles known, admitted, or proved to be true. It clearly explains the process of your reasoning from the known or assumed to the unknown. Without doing this you do not have an argument, you have only an assertion, an essay that is just your unsubstantiated opinion.
The conclusion gives the overall verdict of the argument. You can also restate the ideas that you have discussed in the body paragraphs so as to make your point valid. The conclusion should also aim at motivating the reader to do research in the future. The conclusion is related to the argumentative introduction as the topic as well as the thesis statement is restated in a more convincing manner. The conclusion also gives you a platform of illustrating your decision concerning the argument in the article and why you have settled on that particular decision. Try not to introduce new ideas as they will give the readers an ideology that the article is not comprehensive enough.