What you say in your conclusion should match what you said when you introduced the essay: it should be a restatement (but not a mere repetition) of your thesis, ideally in a way that shows more fully and clearly what you have been arguing. If the process of writing the essay has changed what you are arguing--and this is surprisingly often the case--you may have to reword your thesis in the. introduction Otherwise, the essay will suffer from schizophrenia.
As the diagram above suggests, the triangle of the introduction is inverted in the conclusion. Instead of narrowing, you expand. Begin by restating your thesis, retracing the steps of your argument. By doing so you remind the reader of how the components of the essay fit together and strengthen their cumulative effect. Because this paragraph is a conclusion, you must be conclusive; that is, you must present your thesis in its final, most persuasive form. In the introduction you were giving the reader an idea of what was to follow, trying to attract interest. In the conclusion, you have the weight of the essay behind you, and you can state your case succinctly, knowing that the reader has all the information you have provided.
The introduction is a forecast, while the conclusion is a final analysis. Avoid repeating the introduction too closely; the tone of your conclusion is different because the reader has finished your paper.
Once you have tied up your argument, a good way to conclude is to use the final lines of your essay to suggest a way in which the material you have covered applies to a larger concern. As in the introduction you explained the thesis in terms of a bigger picture, so in the conclusion you can demonstrate the effects or the problems inherent in what you have discussed. For example, a paper on clear-cutting might end with a warning about the consequences of irresponsible logging practises. Remember, however, that an overly sentimental or obvious statement will weaken rather than strengthen your essay ("If we do not save the forests the entire world is at risk").
These concluding lines from Carl Jung's "Approaching the Unconscious" are an example of how a thesis can be broadened at the end of an essay:
Our actual knowledge of the unconscious shows that it is a natural phenomenon and that, like Nature itself, it is at least neutral. It contains all aspects of human nature--light and dark, beautiful and ugly, good and evil, profound and silly. The study of individual, as well as of collective, symbolism is an enormous task, and one that has not yet been mastered. But a beginning has been made at last. The early results are encouraging, and they seem to indicate an answer to many so far unanswered questions of present-day mankind. (94)
The paragraph moves from a conclusion about the subject of the essay to a consideration of the impact of the subject matter (in this case, the study of the symbolic nature of the unconscious mind) upon society.
Never make a claim in your conclusion that is unsubstantiated or even unmentioned anywhere else. New material may enter a conclusion occasionally, but it must be closely related to everything else you have said. Writing "Another character that Helen is similar to is Simon from Lord of the Flies" as the second to last sentence of an essay on Jane Eyre is a poor way to finish a focussed discussion.
Remember the obvious but important fact that the conclusion is the last thing the reader looks at. Do not allow a strong essay to fizzle with a weak conclusion. Always end with a definite statement„as this concluding paragraph does.