The doctor is a very complicated character. He is very pleased with the material trappings of his living room, available to him now that he has the position of medical officer at the baths. The doctor lived a very poor existence for a long time, in the countryside. It is unclear why he was poor in the countryside while his brother was rising through the political hierarchy of the town. More than anything, the doctor seems to be a very enthusiastic, idealistic man--a cross between a revolutionary and an absentminded professor.
Petra shares the doctor's fervent belief in truth and freethinking, as revealed by her discussion with Hovstad and Billing. Mrs. Stockmann, on the other hand, is much more moderate. Although she believes in these ideals, she realizes that they have their limits. As the play progresses, she encourages her husband to consider his family's well-being before he speaks out on controversial issues.
The term "freethinking" is used often in the play. Almost all the characters, except for Aslaksen and the mayor, claim to be freethinkers; it is important to note which of them sticks by their claims and to see exactly what the term "freethinking" means in a closely knit democracy.