Tonic key

In music, the tonic is the first scale degree of a diatonic scale and the tonal center or final resolution tone that is commonly used in the final cadence in tonal (musical key-based) Classical music, popular music and traditional music. The triad formed on the tonic note, the tonic chord, is thus the most significant chord in these styles of music. More generally, the tonic is the pitch upon which all other pitches of a piece are hierarchically referenced. Scales are named after their tonics, thus the tonic of the scale of C is the note C. Simple folk music and traditional songs may begin and end on the tonic note.

In very much conventionally tonal music, harmonic analysis will reveal a broad prevalence of the primary (often triadic) harmonies: tonic, dominant, and subdominant (i.e., I and its chief auxiliaries a 5th removed), and especially the first two of these.

The tonic is often confused with the root, which is the reference note of a chord, rather than that of the scale. The root of a chord is different from the tonic, because many different types of chords (e.g., ii, IV, V) have root notes, and these are not tonic chords. It is also represented with the Roman numeral I. The other types of chords are given different Roman numerals, such as ii for the chord built on the second scale degree, IV for the chord built on the fourth scale degree, V for the chord built on the fifth scale degree, and so on (note: these Roman numerals are referring to a Major key)

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