Traditionally , cadences act both harmonically , to establish tonal centers , and formally , to articulate the end of sections ; just as the tonic triad is harmonically central , a dominant - tonic cadence will be structurally central .
Traditionally , cadences act both harmonically , to establish tonal centers , and formally , to articulate the end of sections . 
 Just as the tonic triad is harmonically central , a dominant - tonic cadence will be structurally central .