A sub assertion is a statement that presents a point of view that supports your main assertion. A sub assertion should be one of these six types of assertions (categorical/definitional, resemblance, ethical, evaluative, causal, or proposal). It should also fit the following formula:
main assertion BECAUSE sub assertion
You will likely have more than one sub assertion in a developed analysis. An excellent way to develop the paragraphs supporting your sub assertions is with close readings of particular passages or scenes.
According to L. Kip Wheeler:
To do a close reading, you choose a specific passage and analyze it in fine detail, as if with a magnifying glass. You then comment on points of style and on your reactions as a reader. Close reading is important because it is the building block for larger analysis. Your thoughts evolve not from someone else’s truth about the reading, but from your own observations. The more closely you can observe, the more original and exact your ideas will be.