Commentary essays are an opportunity to explain the links which different elements of a work have upon one another, and what these elements denote and suggest about particular strands of meaning within the studied subject. This can vary widely depending on the material for which you're providing commentary, but usually it's about dissecting what parts of the work function to achieve certain artistic or informational purposes. Although making points of commentary can be extended, it's perfectly possible to express one in a single sentence.
State the element of your subject for which you'll be providing commentary. This should be specific enough to avoid generalization. While the element you select will vary depending on the work on which you're providing commentary, it should be relevant to the theme or argument of your essay. For example, if you are writing about a novel, you may write something like "The narrator's comments about childhood..."
Write what the element suggests or denotes within the work you're discussing. This should relate to the theme of your essay, and assist you in building evidence about interpreting the work in a certain way. To continue the previous example: "The narrator's comments about childhood imply that he slowly developed animosity towards authority figures..."
Explain the consequence this suggestion has. For example: "The narrator's comments about childhood imply that he slowly developed animosity towards authority figures, which can explain his negative reaction upon learning that his brother has joined the police force." This allows the reader to see what significance one part of the work has on another part of the work or on the larger world.
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