Final answer:
The Dominant (V chord) is the second most important chord in music theory after the Tonic (I chord). It is critical for establishing the key and creating a sense of closure in a piece with its strong tendency to resolve back to the tonic.
Step-by-step explanation:
The question asks which chord is secondary in importance only to the I chord, within the context of music theory. The correct answer is C) Dominant, which is symbolized as the V chord in Roman numeral analysis. In tonal music, the dominant chord, built on the fifth scale degree of a key, is considered of utmost significance after the tonic chord (I), which is built on the first scale degree and provides the home key or tonal center of a piece.
The dominant chord plays a critical role in establishing the key of a piece through its strong tendency to resolve to the tonic chord. This resolution from the V to the I chord gives a sense of closure and rest, which is a fundamental aspect in Western music harmony.