Jean Sibelius gave information about his life in his letters, his diary, his conversations, and in many interviews. He also assisted three of his biographers, Erik Furuhjelm, Karl Ekman and Santeri Levas – and in a way also Erik Tawaststjerna, although during their infrequent meetings in the 1950s neither of them knew that Tawaststjerna would become the writer of the most complete biography of Sibelius. Furuhjelm wrote his book in 1915-1916. Ekman interviewed the composer (by then almost seventy years old) in 1935. Santeri Levas's information is largely based on the composer's communications after 1938, when Levas was taken on as Sibelius's private secretary.
The sources must be treated with caution as regards the views expressed by the composer. In the diary he liked to paint a gloomier picture than the reality. He used the diary as a "spittoon", as he put it, and in it he allowed himself effusions which he would have been ashamed of in conversation, and which he himself laughed at afterwards.
Sibelius said that he always wrote in a tone which he thought would be pleasing to the recipient. The same applies to his conversations, especially in his old age: he preferred to express polite agreement with his interlocutors, or to say something witty or vague, if he did not share their views.
The recollections of Sibelius’s interlocutors are not all equally reliable. Jussi Jalas's notes were written down on the day of the conversation and can probably be considered reliable. However, it is unlikely that Bengt von Törne, writing in the 1930s, could be as accurate about conversations which took place in 1916. Santeri Levas's books (see sources 1945, 1960 and 1960b) quote what Sibelius said (or wrote) in 1938-1957. In the following web pages, if Levas has mentioned the year of a quotation, it is noted in parentheses under the quotation.
Finally, one must bear in mind that the composer's views changed from decade to decade. For example, in 1893-1894 he was an ardent Wagnerian, but later he claimed to dislike Wagner.