This study argues that the overall progression in Il tempo largo embodies an archetypal tonal background, the ^5-Ursatz in C-sharp minor, whereas modal and "modernistic" features emerge locally within this background. At the opening, "modernism" results from a complex chromatic transformation of a tonal model, an auxiliary cadence to A major. The modal episodes involve the cancellation of tonal tensions, first temporarily through the ingenious reinterpretation of the V7 that supports Urlinie ^4, and then permanently to mark the closing ^1. The expressive significance of the modal and "modernistic" elements is discussed, observing how such significance is highlighted rather than impaired by the tonal background. Finally, the first movement of the Sixth Symphony is briefly discussed to demonstrate that modality may operate in Sibelius's music even without a tonal background.