In music theory, the "tonic" refers to the first degree of a diatonic scale, typically represented by the Roman numeral "I". The tonic note is the most stable and central pitch within a musical key, serving as the primary point of rest and resolution in a piece of music. It forms the foundation for the entire scale and tonal system. For example:
The tonic note holds a pivotal role in establishing the key or tonality of a musical composition. It is the note to which other scale degrees and harmonies relate, providing a sense of home or arrival. Musical phrases often begin and end on the tonic note, creating a sense of musical closure and balance.
Harmonically, the tonic chord, also known as the "tonic triad", is built upon the tonic note and serves as the most stable and resolved chord in a key. In a major key, the tonic chord is major, while in a minor key, it is typically minor. For example:
The tonic chord provides a sense of finality and resolution when it is reached in a chord progression. It often follows chords that introduce tension and dissonance, such as the dominant chord, before returning to the tonic to create a feeling of musical fulfillment.
Melodically, the tonic note serves as a reference point for constructing melodies and musical phrases. Melodies often gravitate toward the tonic note, either starting or ending on it, to create a sense of stability and unity within the music.