3. Newton may have been ill all of his life
While some biographers limit his mental illness to the 18 month period during 1692-93, others argue that Isaac Newton suffered from bipolar disorder for most of his life, exhibiting symptoms in early childhood. Newton was a loner as a child, seldom playing with other children his age, instead of engaging in solitary pursuits such as building models of machines and studying their mechanics. His natural father died before he was born, and when his mother remarried he did not get along with his new stepfather. The dislike was returned, and Newton grew to resent his mother for having remarried. He was then sent to live with his maternal grandmother and remained remote from his half-siblings from his mother’s second marriage.
Newton developed a domineering personality, his few friendships throughout his life were with those whom he could overwhelm with his opinions. He also exhibited periods of remorse, during which he wrote out lists of his “sins”, beginning when he was still a child. He was quick to anger, and often violent when angry, lashing out with words and sometimes fists. During his years as a student at Cambridge, Newton wrote in his notes of suicidal thoughts, feelings of isolation, and his readily evident lack of self-esteem. He resented criticism by any other than himself, a feature of his personality which continued through his career when his theories were subject to questioning. The cycle of manic behavior and depression continued throughout his long life.