Apparently, "sensibility" was a popular philosophy at the end of the 18th century. Jane Austen argues that "sense" (being ruled by our rational minds) is better than "sensibility" (ruled by our emotional minds). I read a Times magazine special report on the teenage brain. The amygdala, central switchboard for emotions, is fully developed by the age of 16 but the prefrontal cortex, which judges the consequences of acting on our emotional impulses, is fully developed by the age of 20. The amygdala is the gas pedal and the prefrontal cortex is the brakes. Marianne, who was 16, had a fully developed amygdala but her incomplete prefrontal cortex (the brakes) led her to ignore consequences. What puzzles me is that Mrs. Dashwood was also ruled by sensibility. Her prefrontal cortex should have been fully developed.

"What Marianne and her mother conjectured one moment, they believed the next...". Marianne and her mother believed that Edward Ferrars was in love with Elinor and would propose. Elinor was more rational and realized that Edward's "want of spirits" meant that he probably wouldn't propose. Also, if Mrs. Ferrars knew that Edward wanted to marry Elinor, she would disinherit him because he did not "marry well" (money and social status).