What is the author's tone in Intellectuals by Paul Johnson?

Paul Johnson writes in an academic manner. The book is written in an objective fashion with the author saying he strove to make the book objective and factual. He presents the facts as he found them in various sources which he cites. He drew on letters, diaries, speeches and memoirs as well as books about the group of intellectuals he is examining. He presents the facts he obtained from these sources and presents them in an objective manner without any moralizing or personal opinions.