The way a reader individually understands an idea in a work of literature is known as
inference
interpretation
theme
tone

inference

Explanation:

The inference is a conclusion reached based on evidence and reasoning.

It uses background and observation to conclude and gives a conclusion.

The reader individually understands an idea based on the clues, the theme, characters and all the elements in the story. The readers conclude all the elements of the story, all the clues and make an inference based on seeing and understanding all elements. The inference is an important part of readers' activities because they use available clues or evidence to make a logical conclusion.

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