Intangible
In the book Fever 1793, as the sickness is going around, Matilda tries to stay positive. She can't do anything to fix the sickness other than just wait it out.
During the book, there are some intangible things that happen, including Death, sickness, Love, Sadness, Independence, Childhood, and Growing Up, but some of the main ones are sickness because so many people are getting sick. Death, because it just happens. And love, because throughout the whole book, Matilda stays strong, having her grandpa, mom, and Eliza, whom she loves very much.